Laser Engraving True 8bit Shades of Grey

[Jeff Woodcock]

Hi everyone,

I'm new here and this is my first thread and post on this forum. I would like to introduce to everyone a new process me and my son developed to laser engrave true 8bit shades of grey using a 445nm laser diode. There is no dithering a image first, no pulsing or overlapping dots to get the allusion of shades. What we have developed is a way to vary the laser diodes intensity by analog modulating the laser's driver to get true greyscale. With our setup, we can just use a standard X,Y and Z g-code from any image to g-code rotary engraving type of program for this process. No special laser engraving software or program is required.

Using a laser diode compared to a CO2 to do these engraving is a very slow process, but the results are very gratifying/rewarding for us. This is just our hobby so time to produce them is irrelevant. We have successfully engraved on wood, artist canvas and mirrors with stunning results. With our setup, we can use Constant Wattage and vary the feedrate to get shades of grey, or use TTL to pulse the laser with a dithered black and white image also.

Here is an example of our analog modulation engraving process being used on Birch Plywood.

Jeff

[Dan Hintz]

Welcome to the forum, Jeff.

So you're modulating power instead instead of dithering... it's not exactly a new process. My ULS gives me the ability to set up 16 different power levels based upon gray level. Your second paragraph says you're keeping the power constant and modulating the feedrate instead... that's different, but I'm not sure what you hope to gain using that method.

For the 16 levels I mentioned above... it's not 256 levels, but when the final product of dithering is indistinguishable, it doesn't really matter. I like your output, but why did you select a laser in the visible wavelength range? You're wasting a boatload of your power that way...

[Lee DeRaud]

I'm pretty sure the ULS electronics could generate 256 (8-bit) power levels with nothing more than a firmware change, but I'm not sure it would matter: are there any laser-suitable substrates with that much dynamic range? ("Dynamic range" probably isn't exactly the correct term in this context but I'm drawing a blank.)

[Rodne Gold]

Gcc does 256 levels when doing 3d engraving...
Im not sure what varying power levels will do for resolving photographic type greyscale engraving however , if the laser "burns" the material at the lowest level of grey , it will burn the material at the highest level too..just deeper....aka 3d engraving which a lot of lasers offer...

[Jeff Woodcock]

Thanks for the welcome Dan.

The variable feedrate method was not developed by us, but does give similar 8bit shade results. The first mirror I attached was done by varying the intensity with constant feedrate and the second was done with varying the feedrate with constant power. Both engravings are lit up from the back like a Lithophane.

Our first successful 8bit shaded laser engraving was produced in August of 2012 and we have come a long way since then. Our work has been mentioned on this forum before, but our identity was not given.

We are using a 10bit analog shaft encoder to vary the voltage to the modulated laser driver. The shades are produced based on the axis depth of cut in the gcode. I set the depth in the program to cut -.0256". This gives us 256 .0001" incremental moves to get the theoretical 256 shades of grey. Right now our limitations on power levels are with the image to g-code software, otherwise we could have 1024 power levels (10-bit). Could the different in shades be noticeable from 8bit to 10bit, most likely not, but it would be quite noticeable from 8bit to your 4bit power levels.

We are not wasting any power with the 445nm wavelength either. It has been proven time and time again by us and others that are using them and we all are getting excellent results and burning power. We are able to focus the beam down to a .007" spot using a 3 element glass lens to get the fine detail. We are able to engrave at a 50IPM feedrate with a .008" step over using this 1W 445nm laser diode.

Rodne, we are not 3D engraving. We are engraving 2D images with 8bit shades of grey. I have not seen where anyone has done any 8bit greyscale 2D engravings with a CO2 laser by varying the power. I have only seen connect the dots type engravings that will give the allusion of shades. Can this be done with a CO2?

If anyone is interested, I do have a PDF that I could attach that explains this process in more detail. It has been written by the author of the image to gcode program I use. I assisted in the writing of it, but I do not have any direct commercial affiliation with him, his program or any other links it contains. It has links where to buy laser diode components, link to another forum where we and others have posted there laser diode engravings and information, schematics to build a DAC that uses step and direction pins to modulate the laser instead of using an encoder. It explains things in more detail and I would only attach it for the purpose of discussion only. Would this be allowable under this forums rules?

Jeff

[Rich Harman]

The Shenhuis can engrave at 256 levels as well. They call it "Output direct". I suspect that getting the same results with an 80W laser would be somewhat difficult due to the lowest possible power being too much.

[Jeff Woodcock]

Rich, I can only assume the "Output direct" would be used on the 80W for 3D engravings like Rodne mentioned. Has anyone on this forum tried doing any laser engravings using a laser diode of any wavelength?

[Lee DeRaud]

I still have the question of what material you are engraving. Just because you can send 256 discrete levels of power (or feed-rate) does not mean you can get 256 discrete shades of grey/brown/whatever, especially on things like birch ply.

[Rich Harman]

Rich, I can only assume the "Output direct" would be used on the 80W for 3D engravings like Rodne mentioned

Yes, that is the intended use for that feature. That doesn't mean that someone can't be creative and use it for something that they they never thought of.

[Rodne Gold]

Jeff , The 3d engravings ARE based on shades of grey with power modulation.However , modulating power in the type of lasers we use wont actually engrave shades of grey in *photographic* terms , they will just burn deeper as the power varies

There is no other way to get photographic output on our lasers than to convert to a 1 bit B&W graphic with dithering..which works very well for us.

If you had material that would react discretely to differing power levels , IE "burn" light to darker based on power , varying power might work ..However just about all the materials used here won't do that , yes , you might have a darker mark on something like light wood birch if you apply more power , but all that is is a worse heat affected zone.
Varying speed with constant power will not work with our lasers either , all we will get is a deeper and shallower marking or if the laser is being pulsed , more widely spaced pulses...
It's an interesting application for a low powered and low cost application tho...

[Steven Cox]

I've had a look at the pics Jeff Posted, whilst they do look good, they do show a distinctive banding pattern much like an injet printer does. My images engraved using the Rastus filter the more traditional way on the laser don't show the banding.

[Jeff Woodcock]

Your correct Lee.

The theoretical 256 shades is interpreted by the program I'm using and when lasered on Birch Ply does produce more of a brown shading. That first picture was not a good example other then showing the detail I am able to create with this process.

Here is another engraving that I used white wash pickling wood stain on the Birch Ply first. It starts out white so it's closer to 8bit greyscale.

Steven,

I also attached another mirror engraving that does not have the banding you mentioned that is not back lit. I did not even spray anything on the back either, it's just how it came out of the machine. It's not easy to find good quality mirrors without imperfections and when using a florescent type light causes this effect also.

I don't really like using the variable feedrate method, because it's to hard on the laser diode running at full power for long periods of time.

[Jeff Woodcock]

Dan, I also want to mention that the person that came up with the variable feedrate method uses a 3W 808nm LD and he can not get his laser to burn wood without some kind of coating first like us using the 445nm. He also came up with this method because he has no analog modulated driver to vary the power.

Me and my son developed this greyscale engraving process with no intention of any monetary gain and freely shared this information to anyone that would be interested. Not everyone has the resource to purchase a CO2 and like Rodne stated "It's an interesting application for a low powered and low cost application tho..."

We consider this an open source project and encourage new ideas and input and I just wanted to spread the word on this forum as well.

If you already have a CNC router, then this laser engraving process can be added to your machine. This PDF is for information purposes only for anyone that would like to try laser diode engraving on there CNC machine regardless of what image to gcode program they have or prefer. My setup will work with any of them as you will see in the information that is presented.

http://www.picengrave.com/Laser%20Setups.pdf

Thanks. Jeff

[Mike Null]

Jeff

Welcome to SMC. I see some instances of links that we don't allow on this forum but it is such fascinating reading that I will leave them for others to rule on. While I read the pdf carefully, and I have a vague understanding of what you have achieved, I'm afraid I'll have to retire to the comfort of my workbench and my trusty hammer and chisel.

[Dan Hintz]

Jeff,

I see one major flaw in your logic (though in practice it may not be as big of a deal, depending upon substrate)... substrates do not burn linearly with increased power, so modulating the power does not give an equivalent change in removed material. This is also highly substrate dependent, so one substrate will display vastly different power curves than another... the process would need to be tuned for each substrate. I imagine it's some logarithmic scale for most substrates, and tweaking the exponent would provide a reasonable tune. But the main point is it's not linear, so you can't just set the two endpoints (0 power and max power). Case in point... I can spend hours setting up my 16 levels for 3D engraving when I do a new substrate, and it's never linear... often a curve with a dip or hump somewhere along the line.

For mirrors, dithering is the only way to do it. You either have silvering or no silvering in a spot, there's no shading. I suppose you could apply just enough power so the spot fades from no silvering in the middle to silvering along the edges, but in essence that's simply localized dithering.

My comment about wasting power with the visible laser is about the ability of a substrate to absorb the laser's power. Visible lasers aren't the best wavelength to use for organic substrates like wood... a significant portion of the energy is reflected rather than absorbed. You're correct in that those lasers are significantly cheaper than a typical CO2 cartridge, but then again it's not practical from a business standpoint when a single image can take hours to burn.

[Jeff Woodcock]

Dan,

I do understand what your saying, but our experimenting is evolving and improving as time goes on. What we are doing is allot closer to linear laser control then dithering an image and pulsing the laser. I do have to change power levels and settings based on the different substrates. You all must know pictures presented on any forum does not do them justice as seeing them in person. I do see them totally different then you do. Your correct about mirrors. How many shades are there from white to silver? One difference I see is, there are no dithered dots when lasering these with variable 256 power levels. There are smooth transitions from what little of the shade changes there are, but I do have to disagree that there are no shade differences. I'm not here to argue with anyone, just to present what our outcome of this experimenting has produced.

I'm not doing this for any business purpose either and if you read my posts, it was no way presented in that manner. I own a CNC machine shop and this laser engraving is only a Hobby for us and just wanted to see if others were interested in this process also.

Mike,

I did read the rules and asked the question about posting the PDF and explained what it contained, but did not really get an answer. I thought by Rodne's comment, there was an interest and he is a moderator so I posted it. I do apologize if it does not follow the rules. I understand all this I presented is somewhat backwards to most here with the expensive CO2 machines used by everyone and is not a practical business idea to be considered. I ran across this web site and seen one of my Artist Canvas laser engravings that was posted in another thread and decided to join.

[Vicki Rivrud]

I've had a look at the pics Jeff Posted, whilst they do look good, they do show a distinctive banding pattern much like an injet printer does. My images engraved using the Rastus filter the more traditional way on the laser don't show the banding.

Hi Steven,
What is a Rastus filter??
Vicki

You were probably rolling your eyes with this question! Well after a search here, I found the 3/2012 post and over the net more info - its a Photshop filter - I don't do Photoshop and the Corel plugin is for Corel Painter - don't do that - -after 6 years of learning all kinds of software and getting to know my chinese laser and its software - -etc etc - - Still have lots to learn . . . seems I continue to learn something new each day. Learning CAD & Corel & Photograv was a big achievement too - sometimes a person can just get overwhelmed with needing this and that . . but so it goes :)

[Mike Null]

Jeff

Glad to have you on board. We have a number of members who are interested in the technical side of things and your topic is definitely interesting to them and to us on the fringe. I can imagine even more folks on the cnc forum are keeping an eye on this as well.

I think we all recognize that your intent is to inform and share.

[Rodne Gold]

I really dont think your pdf is in any way contravening forum guidelines in terms of a commercial interest
According to what I read , you use a Z axis encoder to vary power levels , how do you derive the Z axis info -- I don't know Mach3 - so is it some sort of transform mach 3 does to convert greyscale bitmaps to variable Z axis height to do a 3d type carving?
I also note you DO say this wont work for higher powered CO2's
What is the lifespan of such a diode , what does it cost with heatsink et al?
I wonder if such a device could be used to ablate a resist for electro or chemical etching of metals?
What other substrates does this work on? anyone tried clear acrylic?

Anyway , its great that you share this with us , it definitely does have some overlap and relevance to what we do here..

[john banks]

My 100W RECI glass tube has too low a slew rate of its output power to make grayscale engraving commercially attractive. At 1000ipm it is feasible, but I have to run about 100ipm to make grayscale stuff look sharp. Even then, the greatest contrast in wood is between 0 and 8% using TTL switching, rather than between 8% and 90% using PWM output control.

I think titanium could be awesome with the described method from the point of view of the power output, the wavelength and the colors. I've seen a 1W galvo in the UV, visible and near infrared regions make a very sharp and fast image on titanium, but it wouldn't be a good CNC conversion project due to the slow speeds.

It is getting that right combination between controller, power, wavelength, material and speed. There are probably some value propositions using cheaper parts such as a diode and galvo that on the right material could be great?

[john banks]

How about using three channels of audio output from a computer... two channels to control a cheap set of galvos and a third channel to control the power of the diode? Should be much faster if the diode has enough power to mark the material quickly enough.

[Jeff Woodcock]

I really dont think your pdf is in any way contravening forum guidelines in terms of a commercial interest
According to what I read , you use a Z axis encoder to vary power levels , how do you derive the Z axis info -- I don't know Mach3 - so is it some sort of transform mach 3 does to convert greyscale bitmaps to variable Z axis height to do a 3d type carving?
I also note you DO say this wont work for higher powered CO2's
What is the lifespan of such a diode , what does it cost with heatsink et al?
I wonder if such a device could be used to ablate a resist for electro or chemical etching of metals?
What other substrates does this work on? anyone tried clear acrylic?

Anyway , its great that you share this with us , it definitely does have some overlap and relevance to what we do here..

Hi Rodne,

Sorry for such a delay in responding. To answer your question about the Z axis control. First Mach3 is an open source CNC controller program for CNC lathes, mills, routers, lasers, plasma torches, basically any machine tool you want to automate with up to 6 axis control and it runs gcode files. It even has a plugin for engraving photos using a CO2 laser. Mach3 is a Windows based program. http://www.machsupport.com/


I have been making Lithophanes with my rotary spindle in Corian on my servo router with X,Y and Z axis gcode files. Any image to gcode program generates the Z axis moves based on 8bit shaded values of the image. I thought why not try getting the Z axis gcode commands to control a laser in the same manner to burn 8bit shades. I wanted something that the Z axis motor could rotate to vary the power and ended up with the analog shaft encoder, an analog modulated driver and a 445nm laser diode. This was not my first setup or attempt, but like any experimentation over time it improved and progressed to what I am using now.

I have over 800 hours on my laser diode setup already with no failures. From what I have read, the laser diode I am using is from a laser projector, so they have a lifespan in the thousands of hours providing they are not over driven with amps and have a good heatsink. Cost is shown in the PDF and links to components.https://mail.google.com/mail/u/0/images/cleardot.gif

I have built another, more powerful laser where I used two 2.5W 445nm laser diodes slightly angled in the heatsink housing to focus at the same intersecting point. My K2CNC servo router will not run a fast enough blended feedrate to handle the power of this laser, so I'm in process of modifications to that machine. I will be using an encoder again, but tied to a 4th axis servo motor because I can't have the Z axis moving and effecting the intersecting focal point. When bench testing, this laser will actually cut wood and heat resistant automotive gasket material.

At this time, I feel the reason my process will not work with a CO2 to engrave 8bit shaded images has really been explained by you already. You said there are CO2 lasers that does have 256 power levels, but there only for 3D engraving. Imagine the speed it would need to run so they are not cutting into the wood and only creating a 2D shaded engraving. This is what I am trying to overcome on my new build now (lack of speed)

I hope I have some of you thinking about this and maybe someone will come up with a way to do it with a CO2. :cool:

[Rich Harman]

I think the best way to do it with a CO2 is to defocus, set the scan gap to a large value and make a very large image. It would look terrible up close but from a distance it may look quite nice.

[Jeff Woodcock]

I think the best way to do it with a CO2 is to defocus, set the scan gap to a large value and make a very large image. It would look terrible up close but from a distance it may look quite nice.

Here is another members attempt he made after seeing what I have done on another forum, but it was just overlapping the dots. Very good results, but he was still pulsing the CO2.

http://www.sawmillcreek.org/showthread.php?192850-Shades-of-Grey

[john banks]

When I used variable power by grayscale on my CO2 laser it did vary the depth and the shading, but it didn't look as good as dithering (as well as being a lot slower) due to low contrast.

I'm struggling to understand what is being proposed here that is different to existing 3d engraving (that hardly anyone uses on CO2 lasers though) as the power is still being modulated by grayscale information, there is still a heat affected zone and all that goes with that. It appears that running slower with a diode of a different wavelength and lower power gives better shading.

[Michael Hunter]

I'm struggling to understand what is being proposed here that is different to existing 3d engraving ....

I suspect that the difference on wood is that Jeff's low power/low speed method gives different levels of scorching but with little or no removal of material ("depth").
More akin to pyrography than standard laser engraving.

Difficult to achieve this effect with a glass tube laser, since they don't like running at very low power and almost impossible with an RF laser because of the way that they control the power output.

[john banks]

Much more subtle with the low power then.

Can you explain about the RF method of power control - not owning one I assumed you could use a powerful RF tube and ramp up and down the power very quickly indeed with precise control?

[Rodne Gold]

RF tubes do vary the power levels according to greyscale , my GCC's with synrads and coherent Deos tubes do this.

[Michael Hunter]

Dan might correct me on this, but ....

My understanding is that RF tubes always deliver full power when they fire.
Average power (applied to the material) is altered by varying the length of time that the tube is "on" for each dot fired - PWM or Pulse Width Modulation.

When rastering, my (ageing) Epilog only fires on the "grid", set by the DPI setting in the driver.
Possibly the newer ones (with "3D" capability) are capable of firing apparently continuously, but the power level will still be set by PWM.

[Rodne Gold]

It doesn't matter which way max power is varied , it still varies at the substrate whilst the head is travelling at a constant rate according to greyscale ..aka 3d engraving...which is what we are talking about..

[Mike Null]

Michael

You are correct. It is called pulse width modulation (PWM).

[Michael Hunter]

Thanks Mike

Rodney -

Because Jeff's method is much more gentle, I suspect that he is getting varying shades of grey (brown) ***without*** the "3D" effect that the rest of us get.
(The "3D" effect being that the darker areas have (more) material removed so that the whole surface undulates).

If this is the case - perhaps Jeff could confirm yes or no -, then for some images and graphics his method might have real advantages.

Below is a graphic which *does* work in "3D" (although this one was dithered).
Others I have tried have failed because small dark objects come out as holes in the picture and just looked silly.

This was an early trial on BB. The finished item was a little larger and on cherry. The recipient - a stamp dealer - was delighted with his birthday present.

[Rodne Gold]

I recon if you did 3d on our lasers with a teeny variance in power , IE set your max power to 1-2% (lets say 1/2w) and let it do the shades in a range from 0 power to 1-2% one could get the same effect.
The thing is , that the laser is then just burning due to a weak amount of energy being transferred to the substrate , as you say , a pyrographic effect ..
Not really the "right" way the laser should be working , the beam should never "burn" anything , it should zap the substrate with a big jolt , thermally shock and vaporise stuff ...

The value of doing greyscale with a dithered picture is that one can optimise the graphic based on the spot size, substrate and what resolution it can hold and not have to worry about how it will react to variances in power , you set a single power level whose effect on the substrate is is known.
Just about all output we see , computer screen , printing , photos whatever uses some dot format or other

It should actually not be too difficult to mount the diode on a printer instead of the print head and convert the paper feed to a feed table and perhaps get some quite high processing speeds... I used to have a flatbed printer configured this way , based on an Epsom 1290
Big problem with full on 3d on our lasers is the dross and ridges formed on the surface of the engraving as well as not really being able to precisely control the depth.. I have used mine a few times , but find it relatively useless as a commercial process.

[Jeff Woodcock]

Michael,

That came out very nice. To answer your question, no there is no material being removed, but we have experimented with something similar to your 3D laser engraving. We routed an engraving with a spindle on one machine based on the shades and then moved it to the other machine to laser the shades on to it. It was tricky going from one machine to the other and get it to line up precisely. It did not come out the greatest, but here is the results. On our new build we will be able to do the engraving with the spindle and then remove it, slip the laser into the same spindle mount and then paint the shades onto it afterwards giving it the 3D shading effect.

[Dan Hintz]

Dan might correct me on this, but ....

My understanding is that RF tubes always deliver full power when they fire.
Average power (applied to the material) is altered by varying the length of time that the tube is "on" for each dot fired - PWM or Pulse Width Modulation.

When rastering, my (ageing) Epilog only fires on the "grid", set by the DPI setting in the driver.
Possibly the newer ones (with "3D" capability) are capable of firing apparently continuously, but the power level will still be set by PWM.

Yeah, you knew I'd step in eventually ;) Though Rodney did just fine in my absence...

An "ideal" PWM waveform is a series of rectangular pulses. Due to ionization time, etc. with the laser cartridge, each pulse is no longer rectangular... it's more rounded with a trailing edge as each RF pulse pumps up the energy reserves and the gas ionization releases. That's a very vague description and not overly relevant. What's really relevant is how those pulses are applied. Even at low power settings, the actual pulses are nearly full power from the cartridge's standpoint. But, the pulse is so short, the amount of time to do "damage" to the substrate is minimal. As the power setting is increased, more of those full-power pulses are left to dwell on the same spot, locally heating the area and removing/destroying material. RF tubes have very fine controls because of this. There is an issue where too high of cartridge power will completely vaporize material rather than degrade it (i.e., turn it shades of brown), but at the power levels we're typically talking about that's a non-starter (I mention it solely for completeness).

To be specific, an RF tube is likely the best tool for this job, but since it wasn't designed with this job in mind, the user controls aren't typically at the level necessary to do it. With ULS, they give you 16 levels to play with and, as Rodney said, 256 with GCC. I'm happy to see people like Jeff playing with ideas and looking outside the box for solutions, but so far I haven't seen anything novel or anything that is not already being done with just as high a quality as what has been presented.

[Scott Shepherd]

Very interesting results Jeff. Like others, I'm not sure I understand what you are trying to do. I did take the speed and power down to almost nothing and started to get the same type results, although it might be burning it a couple of thousandths in the deepest places. My question would be how long it takes to run. You mention it's nothing more than a hobby, which is great, but what's the run time? Are we talking 1 hour to do 12" x 24", 2 hours? 4 hours?

[Jeff Woodcock]

Hi Scott,

What I'm trying to do is laser engrave 8bit shades without pulsing my laser with millions of dots. It does take a long time for this process, only because of my low power laser diode I'm using. A 9"X7" engraving takes about 3-3.5 hours on Birch Ply depending on the feedrate I run at. I'm estimating with my new laser diode build to cut that time down to around a hour. This being a hobby, not a business, there is no reason for me to purchase a very expensive CO2 with 3D engraving capabilities with 256 power levels to experiment with to get this type of 8bit shading. I probably should have started this thread in the CNC section instead. I seen engraving and posted here because I thought someone would be interested in what I was doing by lasering shades of grey with varying the power of my LD instead.

Hi Dan,

I was thinking that a comparison of quality and shading may be in order. Choose a high resolution photograph, any one online and post a link to it here. You engrave it on the same substrate (Birch Plywood) as I use with your laser machine and process. I'm only specifying that material to be fair so we will compare apples to apples. I will engrave it also with my low power laser diode using analog modulation. Grant you will be finished with yours allot quicker, but that is besides the point for a comparison. Let's say an engraving around 9"X7" in size. You edit/process the photo anyway you need to before engraving and I will do the same. The reason for that size, my plywood is already cut 10"X8". I'm not seeing what you are seeing, because you have not posted any of your dithered laser engravings for me to compare with.

[Lee DeRaud]

I was thinking that a comparison of quality and shading may be in order. Choose a high resolution photograph, any one online and post a link to it here. You engrave it on the same substrate (Birch Plywood) as I use with your laser machine and process. I'm only specifying that material to be fair so we will compare apples to apples. I will engrave it also with my low power laser diode using analog modulation. Grant you will be finished with yours allot quicker, but that is besides the point for a comparison. Let's say an engraving around 9"X7" in size. You edit/process the photo anyway you need to before engraving and I will do the same. The reason for that size, my plywood is already cut 10"X8". I'm not seeing what you are seeing, because you have not posted any of your dithered laser engravings for me to compare with.A simpler (and significantly less subjective) test would be to 'print' an 8x8 grid of 1/2" squares (4"x4" total) covering the 256 shades of gray. This will allow us to see whether those shades can actually be resolved, which I believe is the whole point of this exercise. (Hint: baltic birch is probably one of the worst choices for this test. We need something that starts out a solid uniform color, preferably black or white.)

[Scott Shepherd]

I can't figure out how you'd do 256 shades of gray with a spot size that's .006" or .010" or whatever. Seems the overburn from the next coordinate over would cause problems. But I don't understand about 95% of what's said in this thread anyway :)

[Rodne Gold]

His laser fires continuously and varies power when doing raster type work so he doesn't have a spot size issue as his output is like a solid line with varying degrees of burn (when doing the next line of engraving however , it would have to have a step over of the same width of that line , otherwise the lines would overlap)
Our lasers do this
.................................................. ....
.................................................. ....

His does this
_________________________________
_________________________________

[Scott Shepherd]

But it has to have a beam diameter. The change in power would impact they are before and after the burn spot if the increments of power variation were less than the beam diameter. I would suspect a super small beam diameter would yield the ultimate quality. Or either I still don't understand it at all :)

[Jeff Woodcock]

I able to focus my beam down to .007" and most the time use a .008" step over. How I was able to measure this was to scan the engraving and brought the image into my cad program, made sure it was to scale, zoomed in and measured the burn line. It was a constant .007" width throughout the different shades. There was a .001" line not burned between them which is not noticeable when looking at the engraving from a short distance. The software I use when setting the step over distance which is called Pixel Resolution in the program, will also step over that same amount in the same line it's burning also in the gcode it creates. With that being said, the power level will change every .008" if the pixel resolution is set for that amount, unless the original image shading did not change in that short of distance.

[Scott Shepherd]

I able to focus my beam down to .007" and most the time use a .008" step over. How I was able to measure this was to scan the engraving and brought the image into my cad program, made sure it was to scale and measured the burn line. It was a constant .007" width throughout the different shades. There was a .001" line not burned between them which is not noticeable when looking at the engraving from a short distance. The software I use when setting the step over distance which is called Pixel Resolution in the program, will also step over that same amount in the same line it's burning also in the gcode it creates. With that being said, the power level will change every .008" if the pixel resolution is set for that amount, unless the original image shading did not change in that short of distance.

Okay, now you've gone and really confused me :confused: If you are physically moving the beam over every .008" of an inch, you are, in fact, dithering the image, are you not? Mechanically, not software dithering.

[Jeff Woodcock]

Okay, now you've gone and really confused me :confused: If you are physically moving the beam over every .008" of an inch, you are, in fact, dithering the image, are you not? Mechanically, not software dithering.

No, the laser never turns off like dithering a black and white image and pulsing the laser on and off. Even with white, the laser is still on and the power is just below when it starts to burn the plywood. There are never any dots in my analog modulated laser engravings. Also since my encoder has 10-bit resolution, the power level changed in that short of distance will be theoretically more then the gcode makes it change.

[John Champlain]

Hello group,
I am a friend of Jeff's, and at his urging have recently joined this forum and have been monitoring this thread. Like Jeff, I also have a laser diode machine and am working hard to catch up to his expertise level. I have considered acquiring a CO2 machine, but, being retired, the expense is hard to justify for hobby usage (i.e. I haven't convinced the wife yet :) ).

This has been a most interesting thread, and I am looking forward to learning much from you old timers about the operation and setup of the big machines. Thank you all for your acceptance and hospitality.

John

[Jeff Woodcock]

Welcome John,

I'm glad you finally made it here. Now I won't feel like the Lone Diode Ranger. :)

Jeff

[Jeff Woodcock]

Here is an example of a pulsed laser diode engraving that I dithered the original image using Atkinson. The program I'm using not only is an image to gcode program, it also has editing tools built into it with several different dithering algorithms to choose from.

Since this is the type of raster photographic engraving used by everyone here, I just wanted to show that my machine is capable of this process also. I used white wash pickling stain on the Birch Ply. first.

[Mike Null]

John

Welcome to SMC.

[John Champlain]

Thank you, Mke.
John

[Jeff Woodcock]

Happy Memorial Day

[John Champlain]

Nicely done Jeff.

My new diode has shipped, so my new build should be up and running soon.

John

[Jeff Woodcock]

Thanks John,

Can't wait to see some of your laser diode engravings. :cool:

[Jeff Woodcock]

Well, since no one will post a link to an image and engrave it with there CO2 for a comparison, I will get things started. Here is the link to the photo. http://gfx.galawallpapers.net/photo/76546/Adrianne_Palicki_0.jpg

I used analog modulation to vary the power of my laser diode and used Birch Ply. for this engraving. The size is 9.4" X 7.056" and I ran it horizontal at 50IPM with a .007" stepover. It took 3 hours 13 minutes to complete. I went back over it with a vertical pass at 60IPM with the same stepover and it took 2 hours 41 minutes. I did this in two passes to enhance the shading and detail.

Time it takes really does not matter to me when I'm creating works of CNC art!! :cool:

[John Champlain]

Jeff,
Good job, my friend. I'd give it 5 stars if the forum would let me.
John

[Lee DeRaud]

...so based on your lack of 8bit laser diode engraving knowledge track record, I would say your wrong this time too. :pSo print a gray scale as I suggested before and prove us wrong. The only thing you've claimed about your setup that ours may or may not be able to do is generate 256 distinct shades of gray, but so far you really haven't shown that capability.

[Scott Shepherd]

I still don't get it either. The photo looks decent, but I've seen a lot of amazing work on this forum over the years. I imagine if I spent 6 hours on a 9" x 7" piece, I could yield some of the best results possible on a CO2 laser. However, I don't have 6 hours to work on a piece that size.

I must be missing something. I get the feeling we're supposed to be looking at the most perfectly shaded pieces we've ever seen, and I see nice work, but nothing I consider to be superior to anything else I've seen or done. I've seen some of the most amazing work ever done on a laser by the High Density Optics on a Universal. With a spot size of .0002" or something like that, you'd be hard pressed to see any higher quality in engraving shades and tones, and it doesn't take 6 hours to do a 9" x 7" piece.

Maybe if I was seeing it all in person I'd understand it all better, but at this point, I just don't see the supposed superiority of the engraving. Post the image of the girl and I'm sure some here will take a stab at it.

[Jeff Woodcock]

So print a gray scale as I suggested before and prove us wrong. The only thing you've claimed about your setup that ours may or may not be able to do is generate 256 distinct shades of gray, but so far you really haven't shown that capability.


A simpler (and significantly less subjective) test would be to 'print' an 8x8 grid of 1/2" squares (4"x4" total) covering the 256 shades of gray. This will allow us to see whether those shades can actually be resolved, which I believe is the whole point of this exercise. (Hint: baltic birch is probably one of the worst choices for this test. We need something that starts out a solid uniform color, preferably black or white.)

8X8 1/2" squares does not equal 256, only 64, so how would you be able to count them anyway? I was kinda confused what you were talking about when you requested that. It just did not add up to 256 and was not even sure how to do what you were asking. However, I have lasered 16X16 squares on Birch Ply that does equal the 8bit color pallet (256 shades). I scanned it in grey scale so it will be easier to tell the shade differences. Lee, can you count all 256 shades?

Scott, I do have to admit that the last engraving I posted was not the best I have done. Just like doing any engraving, there is editing involved and I just did not get it as good as I wanted to, but I posted it anyway because it was my last piece of Birch Ply I had. Also, I normally do not do them in 2 passes, so the time would be the 3 hours 13 minutes for this size. Here are two of my better 8bit laser engravings I have done so far. I still have not seen anything here I can compare with and I have not seen any gallery in this forum where others have posted there engravings either.

[Aaron Koehl]

Pretty amazing for a piece of plywood. What is the laser diode process-- is it a home-built machine, a cheaper alternative to CO2, or what? All I can find Googling for "laser diode machine" is laser hair removal.

[Jeff Woodcock]

Thanks Aaron,

here is a video of my machine doing one of these analog modulated laser engravings. In post 13 in this thread there is a pdf file link that explains the process and components we are using.


http://www.youtube.com/watch?v=8xGYtpW00I8

[Rich Harman]

However, I have lasered 16X16 squares on Birch Ply that does equal the 8bit color pallet (256 shades). I scanned it in grey scale so it will be easier to tell the shade differences. Lee, can you count all 256 shades?

I think that engraving the 256 levels would be more telling if done in order from light to dark...

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[Lee DeRaud]

8X8 1/2" squares does not equal 256, only 64, so how would you be able to count them anyway? I was kinda confused what you were talking about when you requested that. It just did not add up to 256 and was not even sure how to do what you were asking. However, I have lasered 16X16 squares on Birch Ply that does equal the 8bit color pallet (256 shades). I scanned it in grey scale so it will be easier to tell the shade differences. Lee, can you count all 256 shades?Sorry, I started typing 8"x8" grid and lost the train of thought somewhere in the middle. That said, with the squares out of order, there's no way to tell how many distinct shades of gray there are in that picture, which is the whole point of this discussion. For instance, are the last squares in the first and second rows different shades? Bloody hard to tell, especially since there are multiple shades of gray within each square.

[Rodne Gold]

Jeff , there are 100's of photographic type C02 laser engraved images on the forum , it's not unique artwork or IMHO, artwork at all unless you took the picture.....
The process you use is , as I have said before ,is not really that useful for most of us here as it relies on material reacting to a burn, whereas most of our lasers work by using a very high energy density to vaporise. The "burn" on wood we get is incidental to the process , its really just resin staining and char , most laser guys don't actually want that side effect when working with most materials ..we try to minimise heat affected zones.

[Jeff Woodcock]

Sorry, I started typing 8"x8" grid and lost the train of thought somewhere in the middle. That said, with the squares out of order, there's no way to tell how many distinct shades of gray there are in that picture, which is the whole point of this discussion. For instance, are the last squares in the first and second rows different shades? Bloody hard to tell, especially since there are multiple shades of gray within each square.

I know it's hard to tell when lasering on Birch Ply because of the grains in the wood does effect the shading, but that is the same effect I get when lasering an 8bit image on the same substrate. My image to gcode program interprets colors based on the 8bit color pallet into the 256 shades and converts that to code for the 256 different power levels. I can bring in a 8bit greyscale image, but it will give me the same results. Can anyone really count 256 shade differences with the naked eye anyway? With that being said, I don't think I can convince or satisfy anyone here on my results of any kind of testing I do.

[Scott Shepherd]

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Here's two images from Universal's website. I imagine both are using their HPDFO system. I think you'd be hard pressed to say the image on leather isn't stunning. They have another photo that's on stainless steel that is really amazing quality, but it's naked baby bottoms and I didn't want to post it on this forum. You can go to http://www.ulsinc.com/markets/graphic-imaging and click on the babies and you'll see it.

I don't think anyone doubts that you have some good images. What I take a little issue with is stating that if no one else posts a photo to this thread, then by default, it makes your images the best on the entire site. There's are literally 1000's of photos on this site over time. Just because you haven't seen them all doesn't mean they don't exist. Just because no one's reposted them in this thread doesn't mean they don't exist and it's not possible.

The work I've seen in person from the HPDFO system on stone has been the best images I've ever seen, period, including your work.

Have you seen the HPDFO system in use? It's work? If not, you really should look into it.

[Jeff Woodcock]

Scott, that is very, very good laser engravings and I thank you for posting them. I hope one day I will be able to get those kind of results with my new 5W 445nm laser diode engraver build. Looks like I need to adjust my beam down smaller to get that kind of detail also. Time will tell.

This is all I asked that someone post a comparison because I could not see what everyone else was seeing. In no means was it a competition, just a comparison request. It's not easy to search for images, only with words and I searched for several.

Thank you for your compliments of my work too. Jeff

[Paul Phillips]

Jeff, first let me say that you do some very nice work, but I think where you've lost most of us is that your bringing a home made hobby laser to a forum where most of us have tens of thousands of dollars invested in equipment that can do what your doing in minutes with better results and wondering why we're not amazed at what you're doing. On it's own it is pretty amazing what you've been able to do with not much money invested, you have a definite talent for pioneering a cheap way to engineer and engrave your own at home, that's pretty impressive, but I think you would be more well received on another forum as others have already stated, maybe the CNC or woodworking forum. To me it's kind of like bringing your Honda Civic to the Ferrari club, ya it's cool for a Honda but we have freakin' Ferraris! If you do a search for photos on here you will find some awesome ones, here's one thread that comes to mind.
http://www.sawmillcreek.org/showthread.php?160081-Some-Recent-Work&highlight=hand+painted+photograph

[Jeff Woodcock]

Thanks for the recognition of my accomplishments Paul. I really do appreciate it. That link you posted to the engravings/paintings is some very amazing and impressive art work, but that process has nothing to do with what we were discussing concerning lasering shades of grey.

[Lee DeRaud]

Your machine must be turnkey and cost a small fortune, or no one here will be amazed.You don't need to spend a lot of money to amaze us, you just need to do something amazing.
Dialing down the attitude about 12dB would help too.

[Ross Moshinsky]

This is a situation of "that's cool but..."

The results look good and it's interesting that you were able to achieve them with such a low cost device BUT similar results can be achieved at a much faster speed with a regular, but more expensive, CO2 laser.

I see a lot of posts on here that I feel fall into that "That's cool but...." category. First, I don't pay much attention to photos of engraving anyway. Catch the right angle and view something from far enough away and it can look spectacular even if it's not. Second, a lot of people on here are hobbyists and what they are displaying simply doesn't apply to us. It's hard to monetize a lot of the things I see posted on here. I typically won't post in those situations but on a rare occasion I will. In this case, I think some people on here are being a bit over critical and harsh in their tone but that's life on an internet forum.

[Hilton Lister]

You do that. It's always interesting to see new ideas and other people's way of doing things. I found your work quite impressive. I have all the tools and software to laser photos
but am seldom happy with the results from a commercial point of view because I find it very difficult to process the photos within in the time you can reasonably charge for.

[paul mott]

Hi Guys,

From reading the comments in this thread it appears that some are perhaps seeing what they want to see rather than seeing or fully appreciating what is actually here.

Like many others I have, for many years now, been re-producing photographic images using the halftone and dot-dithering techniques but the technique Jeff is showing us here is subtlety different.

Initially I did not think this technique would be possible using a C02 laser, mainly because the required variations in output power levels would be less than 2% and all at the bottom end of the power scale. After some practice, advice and encouragement from the diode laser team I discovered that not only is it possible with a CO2 laser but that the results could be quite outstanding. Jeff may argue that I am ‘cheating’ by pulsing my laser at 12.5kHz but that is the just way my CO2 laser varies it’s output power levels.

In any event this is not a totally new technique – most commercial laser machine’s software has handled grey-scale image reproduction for many years now, but in all the instances I have seen they either 'dither', 'half-tone' or reduce the image bit depth to below the 8bit.

I don’t think anybody is claiming that the technique Jeff is presenting here is better than any other technique but for those that wish to embrace it – it could be another string to your bow.

Paul.

[Jeff Woodcock]

Thank you Mr. Mott. :)

That was an excellent explanation! To let you know, I don't think your cheating, I just don't fully understand how your controlling your lasers power. :confused:

[Scott Shepherd]

John, I'm sorry, but what I'm now learning is, your new laser build and engravings will not qualify for the engraving section of the forum either. Your machine must be turnkey and cost a small fortune, or no one here will be amazed.

Jeff, it's comments like this that are putting you at odds with some people. I don't see your point. You seem to portray the cost to do this at nothing more than a red dot pointer, yet you ignore the cost of your CNC machine that it's stuck to. If you add up the cost of your machine, then you can buy a laser, a brand name laser, brand new. How that makes your machine any different than any of ours is something I don't understand. As mentioned numerous times, your photos are very nice. However, they aren't anything that's not already possible, quality wise, with what's available today, off the shelf. That's where the confusion comes in for many of us. I applaud your creativity and what you're developing, I just don't understand it, other than it appears to be a labor of love. People on here, for the most part, have bought lasers to make money. 3 hours run time on a 9" x 7" piece is something most of us can't understand. Perhaps that's the disconnect. No one's saying you haven't achieved something cool. We just can't understand how you make money with it. For you, you seem to have no intentions of making money, so that's fine. But most of us are running businesses and we just don't get it.

For the same money, we can do the same, or so close 99.9% of the public can't tell the difference, we can engrave far more materials, we can do it faster, we can do it more profitable. That doesn't mean we are haters or don't support what you're doing, it just means it's not fair to pretend your machine has no more cost than a $6 laser pointer, when that's just not the case.

What else can you engrave on? Wood? Leather? Paper? Canvas? What are it's limitations?

If I'm not mistaken, you're laser it hooked to this :
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[Jeff Woodcock]

Scott, my name is Jeff.

If you watched my video it shows my mini laser engraver and that is what I am doing this work on. My K2CNC router I purchased many years ago to do rotary engraving. My plans are to mount a more powerful laser on it in the future. How much would a 39" X 24" CO2 laser cost? I don't do this to make money, so the time it takes is irrelevant. I already have the servo router, so it's only practical to make it multitasking instead of buying another machine, especially for just hobby use. Well I say hobby, I will be able to cut gaskets with it for my machine shop business.

I can engrave on wood, mirrors, artist canvas and cut cardboard gaskets so far. I have not tried leather yet, but I suspect the smell would be overwhelming.

I don't believe my posts have been read or followed thoroughly, because I am finding myself doing allot of repeating of information.

[Mike Null]

Jeff

As I indicated early on I was pleased to have you join our forum because you added a new technology (at least to some of us) and you built it yourself.

Like a good many others I do engraving for a living and there are many things that I don't have the time nor inclination to try. But I find this forum valuable because we all share ideas and know how. The hobbyists are especially valuable to me as I regard them as our "test pilots" for new and interesting things we can do with our equipment.

I perceive engraving photographs on wood to be a waste of good wood but I can appreciate some of the results and techniques others have posted.

Would I try to emulate what you've done--no even if I had the time and skill--but I do find it interesting.

Anyway, we've had to remove some posts from this thread for being too contentious and I hope that we can all appreciate the other's point of view without belittling or attacking it.

[Scott Shepherd]

How much would a 39" X 24" CO2 laser cost?

Jeff, what does that have to do with it? Are you asking how much a 24" x 39" laser costs because cost has some role in this? If cost plays a role in this, then that proves the point so many are raising. 3 hours to do a 9" x 7" piece isn't cost effective. So if cost (of the laser) is a concern to you, then why isn't cost of engraving a concern to you. I might spend $40,000 for a machine that large with the high definition optics on it. However, I'll make the difference up in speed when compared to the savings you'll get with the laser.

If time doesn't matter, then why does cost of the machine matter? The two are linked together, not separate. I've asked at for a photo we can engrave to compare, but I've seen nothing yet, but photos of your finished product. If you want to compare things with people, post a link to a file we can use to create something to compare to.

[Jeff Woodcock]

Scott, I was just curious what the cost would be for that much travel on a CO2 because you posted a picture of a router like my servo and was talking about my building costs. I have already posted a picture link in post #53.

Mike or Rodne can you please remove post #77. It's just another personal attack.

Thanks. Jeff

[Scott Shepherd]

Thanks Jeff, I missed that link to the photo. I've downloaded it and I'll give it a try when I get a chance.

[paul mott]

In between the engraving jobs I had a chance to try Jeff’s picture image which he posted earlier. It’s only a scrap piece of wood and the result is a bit on the dark side but it does, I think, illustrate that CO2 lasers can reproduce 8 bit shades of grey without any dot-dithering.

This is only 120mm x 90mm and with a feed-rate of 4500mm/min and 0.2mm step-over took approx 12 minutes to complete.

Paul.

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[John Champlain]

Nice, I just may have to get a glass tube after all for my new machine like you mentioned before.
John

[paul mott]

Naa, your new diode will arrive in the post tomorrow. ;)

Paul.

[Jeff Woodcock]

Paul,

That came out excellent. You sure blew me out of the water with that one.

Can't wait to see Scott's engraving.

Jeff

[paul mott]

Perhaps the most remarkable thing Jeff has presented in this thread is that diode lasers can be used to reverse engrave ‘shades of grey’ into mirrors.
It may not be immediately obvious but whilst the mirror’s reflective substrate is essentially a 1 bit material (either present or not) the mirror’s backing paint is not a 1 bit material - therefore the final effect of ‘shades’ can be produced in a similar manner to that produced on wood, canvas, etc.
I have not actually tried it, but I suspect this process cannot be achieved with a CO2 laser because of the 10.6um wavelength. However, for the enquiring mind, it is certainly food for thought.

Paul.

[Rodne Gold]

Paul , as far as I know , The paint backing is merely a protection of the silvered side , unless the silvered side is actually not 100% reflective , messing with the paint layer will do nothing. In all probability the "greyscale" is achieved by the increase in power changing the size of the vaporised or burned spot due to collateral heat damage...

[paul mott]

Hi Rodney,

You may be right, as I said I have not actually tried the process, but if you take a close look at Jeff's mirror the 'shades' are there. IMO the process not only messes with the protective paint layer's, it also messes with the reflective substrate.

Perhaps Jeff could explain how this happens ?, please.

Paul.

[Rodne Gold]

What we need to see is a macro shot of portion of the engraving so one can see what's actually going on , I have a 10x and 20x loupe and inspect engraving with that , it's an invaluable tool as you can diagnose and see EXACTLY what the laser is doing with respect to the material.

[Jeff Woodcock]

Paul,

when I'm engraving mirrors I have to use the Lithophane setting which reverses the power levels. At full power, which is full Z-.0256" depth of cut in the gcode turns the coating white when viewing it from the front. I have to start out at power level 95 (Z-.0095") for silver. That is the power level just before the reflective coating starts to change and from there is 160 power levels to the white at full power. I can only estimate what I'm seeing and it's maybe only 20-30 shade differences when engraving mirrors, but like you said, there are definitely shade changes.

I used TTL on the very first mirror I experimented with and really did not think varying the power would work very good. The first picture I attached is the very first mirror I engraved by dithering the image B&W and pulsed my laser diode on a cheap Dollar Tree mirror. My wife asked me to engrave an angel for her. :rolleyes: ;) The second picture is the Spirit mirror engraving using analog modulation on a DT mirror that I posted before in this thread when viewed from the back. It looks sorta like a photo negative.

Paul, I don't know if this answers your question or not. If not, I don't really know how to explain what is happening with the either of the two coatings. I just know what I see is a smooth transition from white to the reflective coating to give what shade changes there are.

Your CO2 has more power to be able to implement more of the shade levels on a mirror then my laser diode, so why not give it a try? I did not expect the results I got at first either, but you may be able to get a few more shade changes then I did.

The last picture is an example of how small I can engrave text with my LD engraving machine.

Rodne, I can zoom in on an area and post a picture later to see up close what is going on if you want me to. As you know there is a size limit of pictures you can post here, but I could try to get it close to the max.

[paul mott]

Jeff,

As said previously I doubt that the process is even possible with a CO2 laser because the 10.6um wavelength will also attack the rear surface of the glass causing micro-fractures which will probably appear white in colour and perhaps spoil the overall result.

Thank you for the explanation but as you say I will really have to try it for myself to see just what happens. :)

Paul.

[Jeff Woodcock]

As you can tell, I don't fully understand how the CO2 laser and your setup works because I have never used one. Most here that use a CO2 probably has a hard time understanding how the laser diode process works too for the same reason. I know you started out experimenting with the LD, so you have some experience with them.

[Dave Gabry]

CO2 lasers work on mirrors too. I'm still very new to this new toy, and need more practice to get it right. Photo is of a back-lit mirror tile. Original photo was half-tone dithered then sent to the laser.
Dave

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[John Champlain]

Hi Dave,
Glad to see you've joined us here with examples from your new "toy". I'm looking forward to more as you fine tune that machine.

John

[Jeff Woodcock]

Hi and welcome Dave,

Glad to see you joined us here too. I will be looking forward to your future engravings also with your new CO2 machine.

Dave is the one that designed the first DAC electronic control circuit and implemented the step and direction output pins in Mach3 to vary the laser diode's power to engrave shades of grey. He used X,Y and C gcodes for this process instead of my X,Y and Z. Considering what this discussion in this thread is all about, this is important information I want to share with everyone.

Here is a picture of one of the back lit mirror engravings where I zoomed in on a section of it. I used a back lit one because the reflected areas will show black instead of silver so it's easier to see the shade differences. It still is really difficult to count them though.

[paul mott]

Hi Dave,

It's difficult to tell from your photo but are you able to get 'shades of grey' or is it just the 'illusion of shades' as a result of the dot-dithering. ?

A closer photo of just one part of that montage would be nice, please.

Paul.

[paul mott]

Hi Dave,

Please ignore my earlier post - I have just been told that you are using the FSE laser which converts the image to 1bit before dithering so my question has been answered. ;)

Paul.

[Rodne Gold]

As you can tell, I don't fully understand how the CO2 laser and your setup works because I have never used one. Most here that use a CO2 probably has a hard time understanding how the laser diode process works too for the same reason. I know you started out experimenting with the LD, so you have some experience with them.

We have no hard time about understanding how a laser works , co2 , yag , diode whatever..the point we are putting across to you is that you are working with a VERY narrow band of power and modulating it to get larger or smaller heat affected zones rather than using the power density to thermally shock and ablate or vaporise substrate..

I could do exactly the same thing that you are doing with the diode laser with my GCC Synrad tubed Co2 if I set its power low and told it to do 3d engraving which uses 256 power levels and uses a greyscale image ..it would use power level 0 for white and 256 for black and if for eg I set power levels between 0 and 2 watts to do this , I would get 256 levels varying from 0-2 watts and get the same results as you depending on material used , no dots or dithering required. The wavelength of your laser might have slightly different effects depending on how the material aborbs it..
I couldn't do the same with my Glass Co2 tube , but thats not because it's incapable , but because they do not fire reliably at less than 15% power and on a 60/80w tube , the minimum power level would be too high..

[Jeff Woodcock]

Rodne, I know you understand and you made that very clear before. There were others that did not fully understand and I sure don't understand exactly how the CO2 laser process works because I have no experience with it. I'm here to learn too and you sure are a wealth of information and I thank you for that.

[Lee DeRaud]

...the point we are putting across to you is that you are working with a VERY narrow band of power and modulating it to get larger or smaller heat affected zones...If that's actually what he's doing, then it's basically a form of half-toning. The 0.007" stepover translates to about a 140-dpi screen, roughly newsprint quality.

[Jeff Woodcock]

If that's actually what he's doing, then it's basically a form of half-toning. The 0.007" stepover translates to about a 140-dpi screen, roughly newsprint quality.

This was the point I was trying to make earlier. Lee, you don't fully understand what my laser engraving process really does. It's not DPI, but LPI. Lines Per Inch. The lines do not vary in width with the different power levels as I explained before and it is not halftoning either. Halftoning is a dithering algorithm which I do not use any dithering at all. I always bring in a 24bit color image into the program I use, then it averages/reduces it to 8bit for the gcode generation. My encoder has 10bit resolution and Dave and John's DAC can be built to have 10bit resolution also, so that may be the advantage we will have in the future with more development and experimentation.

Lee, Rodne explained it like this before.

A dithered pulsed laser engraving is like this.

.................................................. .........
.................................................. .........

My analog modulated engravings are like this.

_____________________________________
_____________________________________

The attached is an analog modulated laser engraving that is zoomed in close to see what is actually happening when I engrave on Birch Ply. The slightly angled vertical lines are the grains of the wood and how they effect the burn line and image. You can faintly see the horizontal lines where the lasers burning paths meet one and another when it steps over. These line do not change in width throughout the varied laser's power levels.

If I can figure out how to focus the laser beam smaller then .007", then my detail will get allot sharper and would be able to use a smaller stepover. I'm only asking this question out of curiosity so I can learn more about CO2's. What are the average size of the focused beam and what is the stepover that is being used with them? Not necessarily what the smallest size it can be focused and the minimum stepover it's capable of, just the average most use to be productive and still get visually good results.

[Rodne Gold]

Due to beam wavelength , the best spot you can get with a CO2 , assuming perfect beam quality and a good lens is around 0.003" , most lasers will allow a 1200 dpi stepover , or 0.0008"
The problem with using a stepover smaller than the spot is that the spot overlaps and causes more heat affected zones , actually reducing the resolution due to "dot gain"
So effectively the best resolution of a 0.003" spot size is to run at the same stepover as the spot , IE 300dpi

However there is another consideration , and that it the DPI a medium can resolve , canvas , wood etc can not actually even resolve 300dpi for various reasons. Materials like black anodised aluminium can..You have to understand what the laser is doing to any material .. for eg into wood , you are getting the colour via staining and char , on anodised aluminium , the laser actually vaporises the dye use to give it colour , without touching the anodising and so on...

As a commercial operation , the secret is to balance resolution and time , a 500 dpi stepover will take 2x as long as a 250dpi and will most likely not actually give better results , most customers would in all likelyhood be more than happy with 120dpi ...but if you CAN do better as an engraver..you do so..

To put things in perspective , most guys here charge on a time base..$1 a minute or so , a 5 hr 10" x 10" graphic would cost the customer round $300 or more..no customer of mine will pay that....

[Scott Shepherd]

This was the point I was trying to make earlier. Lee, you don't fully understand what my laser engraving process really does. It's not DPI, but LPI. Lines Per Inch. The lines do not vary in width with the different power levels as I explained before and it is not halftoning either. Halftoning is a dithering algorithm which I do not use any dithering at all. I always bring in a 24bit color image into the program I use, then it averages/reduces it to 8bit for the gcode generation. My encoder has 10bit resolution and Dave and John's DAC can be built to have 10bit resolution also, so that may be the advantage we will have in the future with more development and experimentation.

Lee, Rodne explained it like this before.

A dithered pulsed laser engraving is like this.

.................................................. .........
.................................................. .........

My analog modulated engravings are like this.

_____________________________________
_____________________________________

The attached is an analog modulated laser engraving that is zoomed in close to see what is actually happening when I engrave on Birch Ply. The slightly angled vertical lines are the grains of the wood and how they effect the burn line and image. You can faintly see the horizontal lines where the lasers burning paths meet one and another when it steps over. These line do not change in width throughout the varied laser's power levels.

If I can figure out how to focus the laser beam smaller then .007", then my detail will get allot sharper and would be able to use a smaller stepover. I'm only asking this question out of curiosity so I can learn more about CO2's. What are the average size of the focused beam and what is the stepover that is being used with them? Not necessarily what the smallest size it can be focused and the minimum stepover it's capable of, just the average most use to be productive and still get visually good results.

That's where you lose me. I think exactly the same way Lee does and I expressed it at the beginning of this thread. Here's my problem with saying you're not half toning-

You're using a beam diameter of .007". There's no way to not dither. You might call it something else, but that beam diameter is changing power levels or intensity as it moves. So if you have a square and half is solid black and half is solid white, at the transition point, it's going to be a .0035" over burn or under burn. The fact you are cutting with a round dot means you have to be overlapping the dots. You have to. There's no other way to avoid it. For example, if the power level is 50 at X.000, and 0 at .004", then you have an overlap there where something is getting burned too much or not burned enough. With the images you post, it doesn't matter, because it's a larger image and it all blends, but it's not any different than what CO2 lasers are doing. You can say it's :

- - - - - - - - - - - - on a CO2 laser, but I can pulse that at 1000PPI, so the end result is going to be :
________________, which is the same thing you are doing.

I just don't understand the difference. I think your method might be a lot more gentle on the material, to some degree, but slowing a CO2 laser down to super slow speeds would probably get you the same results.

[Rodne Gold]

Scott , if he varied power , His line would look like this

[Jeff Woodcock]

Thanks for your input and information Rodne and Scott.

There may be some interest here what we are doing at a Hobby level, not as a business, that would like to learn to build one for them self at a more reasonable price then buying a commercial CO2. Another advantage would be the CNC router can be multitasking. You can do rotary engravings like reliefs on wood or create Lithophanes in Corian. Pull the spindle, then insert the laser and engrave photos either by TTL or analog. You would not believe how much money I saved by making Christmas presents instead of buying them the last couple of years. They were all appreciated much more too.

[Scott Shepherd]

Scott , if he varied power , His line would look like this

Does not. That's my point. In theory, that might be what happens, but when you at a .007" diameter cutting tool (the laser) to it, you HAVE to have over and underburn. There is no way not to.

I don't know if this explains it any better, but even though it's a continuous movement, you still have this going on.

263630

[Lee DeRaud]

Scott , if he varied power , His line would look like thisThat assumes the beam is hitting a substrate that actually changes color proportionally over the full range of the laser's output power. There may be such substrates out there, but wood isn't one of them.

He is varying the power over an 8-bit (10-bit?) range: I accept that at face value. The problem is, I really don't care what the output power of the laser is doing, I care what is happening to the substrate the beam is hitting. Jeff seems to believe it's the same thing...I don't.

[Rodne Gold]

Yeh..I agree..his method assumes the substrate can resolve 256 levels of darkness of burn... the "resolution" which I doubt that could be anything like 256 levels , is most likely aided in some respect by the "width" of the engraved line modulating due to dot gain.

[John Champlain]

I believe that what Jeff, I, and others are working to perfect and improve with our laser diode imaging process might better be described as "continuous-tone" imaging. There are no "dots" or half-toning involved, but rather a smoothly varying shade change between one pixel and the next in an image, aided by the constant velocity (CV) algorithm of the Mach3 CNC control software we use. Each pixel burned by the laser beam is smoothly blended into the following pixel.

Lee is quite correct, in my opinion, that wood does not likely shade evenly in 256 steps from one surface point to the next in response to the degree of power absorbed(?) from the laser beam, but it does appear to shade close enough throughout a complete image so that to the eye it does appear to be doing so. Proving or disproving whether or not wood burns truly proportional to the applied laser power is near impossible with the tools we have available to us today, and is not really debatable with other than personal opinions at this time. A Google search has so far failed to produce any documents relating to the subject.

The diode imaging process also appears to be aided by the spacing of the scan lines of the final images. Currently we are only capable of "scanning" at a step over distance of 0.006 to 0.008 inches due to limitations in the currently available optics we have available to use. The spacing between scan lines (unburned wood) seems to help lighten some images.

We are also generating continuous-tone gray scale images with two different methods, variable power (analog control) and variable feed rate (constant power). The variable feed rate method (VFR) varies the velocity of a fixed power laser beam proportionally to the pixel shades of an image, thus allowing the substrate (wood or whatever) to burn lighter or darker shades. In some instances, I believe the VFR method may be better than the analog method at producing gray shades, depending opon the substrate used, and we have not yet fully explored either method to determine which is best.

This discussion is not intended (never was) to be a debate of which laser imaging method is better/best. What Jeff started out in this thread to show was a different method of reproducing an image with a low cost laser diode. The subsequent discussion has been very informative and enlightening in its entirety, and I believe we have all learned (are learning) a lot about our different methods and the equipment we use. Comparing commercial needs and hobby needs will hopefully not interfere with our future appreciation of each others work and interests.

Thank you all,
John

[Jeff Woodcock]

Well said John!

[Scott Shepherd]

I believe that what Jeff, I, and others are working to perfect and improve with our laser diode imaging process might better be described as "continuous-tone" imaging. There are no "dots" or half-toning involved, but rather a smoothly varying shade change between one pixel and the next in an image, aided by the constant velocity (CV) algorithm of the Mach3 CNC control software we use. Each pixel burned by the laser beam is smoothly blended into the following pixel.

John, that's what many of us have been saying, that CO2 lasers are perfectly capable of doing the exact same thing. It is no "automatic half toning" that happens to every single file. You can take a b/w photo (or color if you wanted) and burning varying shades of gray, all continuous.

My reasoning for not being able to get a lot more detailed about the results from it are based solely on the fact that we learned years ago that it was virtually impossible to make money with, so we've spent little to no time working with it. At trade shows, every laser manufacturer has photos of babies or weddings engraved on stone. It's pitched as a great product. They just don't explain it takes 50 minutes to laser and the average retail person won't spend $75 on a tile. So, in reality, it's driven most people away from experimenting with photos too much.

I feel like I say this in every post (because I don't want you to get the wrong impression of what I'm saying). I think your results are really nice and look great. I still don't understand what you're doing that can't be done on a CO2 laser.

[paul mott]

Steve,

Yes, true 8bit shades of grey engravings (without dithering) can be done with a CO2 laser (see post #79) but I doubt that many will actually try it. :)

Paul.

[Scott Shepherd]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

[John Champlain]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

Hi Scott,
What you say is fully accepted. I don't want to go back through all the previous posts to try and determine how this thread may have turned into a discussion of commercial CO2 vs. hobby laser diode, and it really doesn't matter anyway as that was never the original intent. I think that saying that it (laser diode method) is different can not be arguable, and I certainly will not argue which process is better or worse - it doesn't matter anyway. The two processes are really serving different markets.

What I will say is that Jeff did invent and develop, and continues to perfect, a new method of image reproduction, and his market is the hobby users who want to reproduce images at a lower cost than CO2, and who do not care about the time it takes.

Thanks again,
John

[paul mott]

Paul, I saw that post and it proves what I've been saying from the beginning. I don't understand what it's doing that can't be done with a CO2 laser. I keep getting told it's different, but I have yet to see anything that can't be done with a CO2 laser.

Steve,

I think you are quite correct - commercial CO2 laser machines operating software's have offered exactly this method of image reproduction for many years now - However, if you were prepared to spend just 12 minutes of your time trying it I am certain you would understand why / how Jeff's method is different.

Paul.

[Scott Shepherd]

Paul, what's the 12 minute version? I was prepared to give it a whirl this past weekend, but when you slow the machine to the point where it's in the 1-2% range on things, to get this superfine detail and results of variations of power, it's slower than watching paint dry. I didn't have 2-3 hours to let it (and my exhaust) run to get results. I did engrave a few lines and I didn't see anything I didn't expect to see.

What's the 12 minute version? At 20% speed or 40% speed, you won't see the same thing, as Lee mentions, burning wood at higher speeds isn't going to get you the darker results. You have to use slow speed and low power.

I understand the goal now, to produce a product for people without lasers. That's fine. I thought the hype was from the quality, not the application, and that's what I obviously misunderstood from the beginning.

I still don't see the value at 3 hours of engraving for that small size. I think it's a nobel cause, but if you can do something yourself on a CNC router with a laser diode and it takes 30 hours of run time, or you can sub it to someone with a Vytek and get it done in 3 hours, it would make a lot more sense to sub it out. You'll never compete with something like a Vytek in that market. That's a different discussion, I suppose. I think I'm done trying to understand it, from a business standpoint.

[paul mott]

Steve,

Sorry to keep going round in circles but you made the statement 'I don't understand what it's doing that can't be done with a CO2 laser'.

Jeff posted an 8bit .jpg image earlier, I ran this direct from the image (without dithering) but reduced the overall size to 120mm x 90mm and it took 12 minutes to complete (Post #79 relates).
I don't have a super fast laser, my axis speed was 4500mm/min and the step-over was 0.2mm. OK, my result is not that brilliant but it was just a trial and I am sure that if you are prepared to try it for yourself you would then understand. ;)

You refer to 2 - 3 hours, where does this come from ?

Paul.

[Rodne Gold]

MY laser resolves 256 power levels from greyscale without all manner of external devices and without 1/2 toning..called 3d engraving.
Nothing new , despite the protestations otherwise , it's just re- inventing the wheel in a very clumsy kludgy manner to boot...

[Scott Shepherd]

It comes from an earlier example saying that a 9" x 7" engraving took about 3 hours to engrave.

You can't run the machine fast to get that level of contrast in wood. You have to run it very slow with very low power, which is where the slow times come into play.

[paul mott]

You can't run the machine fast to get that level of contrast in wood. You have to run it very slow with very low power, which is where the slow times come into play.

Steve,

Do you consider an axis speed of 4500mm/min to be fast. ?
Surely, if I can CO2 engrave that image in 12 minutes you can do the same thing. ?

Perhaps I am misunderstanding the capabilities of the commercial laser machines.

(I think the 9" x 7" example taking 3 Hours was relating to diode engraving not CO2).

Paul.

[Jeff Woodcock]

This is how I look at the time it takes to engrave on my machine. First, it's a Hobby, so time is irrelevant. Second, it's paid for so it's not an asset I have to constantly be making a product with to make a profit, or to pay for the machine. Third, it's a CNC machine so it when I start it, I can go and do paying jobs in my shop while it's running, or even go home for the day. It turns off by itself and the engraving will be finished when I get back.

Rodne, that comparison is like comparing go kart racing to NASCAR. Both are a form of racing, but one is just faster then the other and the purse is bigger when you win. I don't think the go kart racers believes there sport is clumsy or kludgy if they come up with new ways to improve there sport. I don't feel what I am doing with the laser diode is either.

[Scott Shepherd]

Paul, correct me if I am wrong, but your sample didn't look like baltic birch. In order to get that dark color in baltic birch, you need to either go fast with a high power, or slow with a low power. If you run it fast with a high power, it skips over a lot of the lighter colors. If you run it really slow, you can get much better contrasts between the light and dark on something like baltic birch plywood.

[paul mott]

Steve,

The wood I used was 3mm Obeche. (I think you are perhaps confusing my work with Jeff's). ;)

Paul.

[paul mott]

Jeff,

I still remember first seeing your work last summer and being totally amazed. My initial thoughts were that it could not be reproduced with a CO2 laser for many of the reasons that others have mentioned in this thread.

Together with my big brother (Mr.T) we set out to try and it was not an easy road. John may recall seeing some pictures of the early attempts where we were cutting 4mm deep into the MDF in the darker areas of the work before we got the balance between speed and power on track. This is one of those areas where practice makes perfect but, of course, we never ever reach the perfection but there is always improvement as we continue to learn.

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Keep up the good work my friend.

Paul.

[Rodne Gold]

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Paul the reason most of them don't offer that option for photo engraving is that most substrates are 1 bit and it would be useless for them ... and those that can resolves "shades" are way to fiddly to work with and get it just right..

[Scott Shepherd]

Steve,

The wood I used was 3mm Obeche. (I think you are perhaps confusing my work with Jeff's). ;)

Paul.

Paul, I'm not confusing the two. He posted photos done in Baltic Birch. You posted a photo showing it done in some non-baltic birch product. He said to burn the baltic birch, it took 3 hours (actually closer to 6, he ran it twice), but he said he can do it in 1 pass if needed. So I took 3 hours. I said your photo took less time because it was done in a wood that burns a lot darker than baltic birch. My comments about time were based on trying to replicate exactly what he posted, not simply engrave the same photo on something that works better than the substrate he specified.

So no confusion on my part, but I probably didn't explain it well enough on who/what/where I was referring to. Sorry about that.

[Jeff Woodcock]

Thanks Paul,

I use the cabinet grade Birch Ply. only because I got it cheap and I have a stack of it. The hardest part of this engraving process is, cutting it up into usable pieces. :)

[Lee DeRaud]

Do you consider an axis speed of 4500mm/min to be fast. ?That's ~175ipm. ISTR Jeff's CNC machine was operating at 20ipm, so yeah, for the purposes of Steve's explanation, that's "fast". But most of the commercial CO2 machines will raster upwards of 1000ipm, so it's also "slow"...context is everything.

One last thing before I leave...

The whole premise of this thread is "Dithering is bad." But it's not: it removes the grossly inadequate material tonal response from the equation. Laser off equals pure "white" (to the full capabilities of the substrate), and usually you can obtain pure "black" over a rather wide range of laser power. You're not diddling around trying to match a rather narrow and nonlinear tonal response curve to the tonal range of your input image.

Think about this: have you EVER seen a photo "printed" by a laser engraver (CO2 or diode) that has as wide and smooth a tonal range as the output of a simple $100 monochrome laser printer? I think not.

[Jeff Woodcock]

Lee, if your talking about me, I run mine at between 40-60IPM depending. Feedrate effects how dark or light I want it. Most the time I run at 50IPM. My new build on my servo router should be able to engrave between 150-200IPM with the increased power of my laser diodes.

Also, you are the first one here to say dithering is bad. No one ever said that anywhere I have read in this thread. I do use dithering on harder to burn materials also. It's either full power or none. I even posted an engraving in this thread that I dithered the image and engraved it by pulsing my laser diode. The Birch Ply. had white wash pickling stain on it which makes it harder to burn. I have a few different options my machine can engrave with.

I'm still trying to figure out who Steve is. :confused:

[Scott Shepherd]

I'm still trying to figure out who Steve is. :confused:

Read my signature :)

[Jeff Woodcock]

I have been so busy reading the posts, I never did read that. :rolleyes:

[paul mott]

Just a generalisation but it appears that all commercial CO2 laser machines are capable of producing true 8bit shades of grey (without dithering) but it seems that none actually do (perhaps with the exception of the machine manufacturers sales literature photo’s).

Paul the reason most of them don't offer that option for photo engraving is that most substrates are 1 bit and it would be useless for them ... and those that can resolves "shades" are way to fiddly to work with and get it just right..


Rodney,

I think you are absolutely right. As far as CO2 lasers are concerned most substrates are treated as being 1bit.

I may be wrong (and I stand to be corrected) but I think the reason Jeff started this thread was to educate us all to the fact that some substrates will handle 8bit resolution. I accept that it may be fiddly to set-up and the process is not for everybody but I am all for learning anything that I cannot already do. One day the additional knowledge may come in handy. ;)

Paul.

[Jeff Woodcock]

Thanks Jeff, I missed that link to the photo. I've downloaded it and I'll give it a try when I get a chance.

Scott,

You have not had a chance to try it yet?

I requested a new function to the image to gcode program I use to ignore any areas where the background has been cut out or if there is any larger pure white areas when using the analog modulation settings. Before it would only do this when using TTL modulation with a dithered B&W image. The author did some reprogramming to his software and now the laser will not run in any of those areas to save on engraving time. This is the same image I engraved before and I did it in one pass this time at 50IPM. It is the same size as the engraving I posted before and it cut down 36 minutes off the first pass engraving time that was set at the same feedrate.

[paul mott]

Jeff, nice work. Just out of curiosity you say that you reduced the job time by not scanning the background.
Did you have to Photochop the artwork (from Post #44) or did you software reduce the bit depth to achieve this ?

Paul.

[Jeff Woodcock]

Thanks Paul,

I just used Corel Photo Paint's Magic Selection Wand to select the background and then cut it out. It was easy to select when the background was all one color in the original image. When saving the image file, Corel will make that cut out background area pure white. This area being white when brought into PEP4PL, it will just ignore those areas now when generating the gcode. My settings were the same as before with the .007" pixel resolution and the feedrate. The laser beams path just went back and forth to the edge of the image instead and it just ignored the background area and that is how it saved on the engraving time.

Jeff