Engraving photos onto clear acrylic

[Ben Fenton]

Hey folks.. hope we are all well : )

Basically, I've recently bought a 120w co2 laser to mainly cut acrylic. I've been trying for a couple of days now, wastefully I might add, to engrave a grey scale picture onto clear acrylic. Its only for a gift, but was hoping to achieve an effect similar to this:


I simply cant work out what they have done to achieve this level of detail? I've tried grey scale, which does output as grey scale as proven with varying power output, even though the colour of the entire engrave is fairly similar, and I've tried the gold method which whilst looking good, looks in no way as 'pleasing' as the pic above

Using laser works v5, I've tried different dpi, different powers, different speeds, and different step intervals (or whatever you kids call it) where by the distance the laser head moves down per pass ranges from 0.1mm, to 0.27mm. The only difference this makes is a visible banding when the laser head jumps to far and leaves a section of the material untouched

I'm babbling now, but hopefully someone will be able to guide me where I'm going wrong. In short, how have the got the effect shown in the link :D

Thats simpler to understand ;)

Thanks in advance for any advice you have

[William Wong]

laser machine can do a lot of work on acrylic...we can make any design from software and we can engrave and cut acrylic by laser machine269484269485

[Ben Fenton]

Ok

Anyody else? ; )

[Dan Hintz]

Ben,

Maybe you have missed an important step... difficult to tell from your description, but maybe this will tip you off.

Starting with a greyscale image is a good first step, but you have to keep in mind that acrylic will not show greyscale based upon differing power levels (the holes will just be varying depths). To achieve that greyscale look, you need to consider how newspapers do it... they use a single color (black) and get a greyscale image, but they do it by varying the density of the small dots. More dots in the same area means it looks darker. This is what you're trying to achieve. So, I think the step you're missing is changing the image to 1-bit color before engraving.

Only change to 1-bit color as a last step... do not resize the image after the conversion. Shoot for around 300 dpi to start with and work your way up as things start to look right.

Try that and get back to us...

[Ben Fenton]

Thanks Dan : )

Yeah, i'm definately missing something. Ive kinda given up on actual greyscale as like you say it doesnt work, and just produces a fairly uniform colour on the acrylic, loosing any kind of detail. So, ive starting playing around with the 1-bit idea. From the sound of things, I have been making the pictures far too low as far as dpi goes, as I assumed a higher dpi would just cause the laser to repeatedly go over the same line twice or more. I'll make another image at 300dpi and let you know how it goes : )

Thanks again

[Scott Shepherd]

I don't do all that stuff, but I do know one thing. The laser doesn't like the same thing your eyes like in a photo. If you convert it to grayscale, you need to mute the light and dark areas. I describe it as making the photo look "washed out". If you saw the photo, you'd say "That's horrible", but it engraves very nicely. You don't want wide swings in contrast. You want a very bland, blah looking result.

Next tip would be that you want very low power. Just enough to mark it. Maybe a tiny bit more. But if you overpower it, it'll give you a really poor result.

300DPI, washed out photo, light power, apply a stucki or jarvis filter to it and you'll be all set.

[Martin Boekers]

Search here for the Gold Method it will help in the conversion process, here is a way to do it in Corel. http://www.youtube.com/watch?v=yllZTBA0HO0&feature=related YouTube is your friend... :)

[Brian R Cain]

Just to elaborate slightly on what Dan is saying, when you engrave a grayscale image, the laser output will vary depending on the shade of grey. There is a threshold that the acrylic needs to be heated to in order to get it to engrave cleanly. Using a greyscale image might mean that there isn’t enough energy been used in the light tones to cause any reaction on the acrylic. Increasing the power can overcook the darker tones.

By converting the image to black and white, the laser is either turned on or off, so all that’s required is to use the power and speed settings that engrave acrylic cleanly. One other thing to remember is that the laser is turned on by the black parts in the image, which then cause the acrylic to turn white. You need to invert the image before you engrave it.

[Dave Sheldrake]

120 watt Glass Tube Ben?

If so then the strike minimum (about 10%) will likely be too high for decent engraving. Also make sure you are using cast acrylic, Extruded doesn't engrave very well at all.

For cast acrylic I typically use 10 - 12% power on an 80 watt system, (circa 8 watts) on a 120 that's going to be proportionally higer due to the low power minimum required.

If it's an RF, ignore me :)

cheers

Dave

[Martin Boekers]

Ben, make sure you are using Cast Acrylic, extruded can't reproduce the "frosted look" of Cast.

[Ben Fenton]

Hey,

Thanks for the replies : )

Ive played around and made a 1-bit image based on a random image of vegas from google. Originally, the image had a res of 1500x1000, so fairly small. I increased the dpi, inverted and adjusted to make washed out and it produced a nice looking image when engraved. The dpi worked out to 500dpi. Now, obviously the dpi is linked to the scan gap, and the specs of the machine (which is glass tube btw) suggests its capable of 1200dpi. This means a scan gap of around 0.025. Is it worth carrying increasing the dpi or does it become pointless after a certain number? I assume it does. Plus, it starts to take quite a while to engrave

Also, will starting with a bigger picture res wise, make a better end result? Im getting there though, so again, thanks for the input : )

And yes, its cast acrylic

[AL Ursich]

Another option is to convert the photo to a Sketch where the software has a slider and makes sketch lines. It might give you something to work with. Do a search on photo to sketch programs.

Great Lakes NTC 1985 behind the Boat House Bldg 13. I had just made Chief Fire Control Tech.

AL

[Ben Fenton]

Thanks Al, I'll keep that in mind

For what its worth, I ran an image at 500dpi with a scan gap of 0.05 (~500dpi), and then reworked the image to 300dpi with a scan gap of 0.085 (~300dpi) and from what I could tell, more detail could be seen on the 300dpi version. So maybe the dot size of my laser cant handle 500dpi?

Also, my laser tube half way through the second run stopped firing completely. Someone doesnt want me to work this out ; )

Hopefully getting it sorted tomorrow, but I think the tube may be broke. I dont know enough about them to say for sure, but there appears to be a burnt area near to the first water inlet. The tube comes to life im some respect whenever its told to fire, but its more of a flame towards the inside of the tube at the start. Not the beam ive seen since when searching reci tubes on youtube. So something is definately wrong some where

Suprising, as reci's are supposed to be good tubes I thought?

[Chuck Stone]

Thanks Al, I'll keep that in mind

For what its worth, I ran an image at 500dpi with a scan gap of 0.05 (~500dpi), and then reworked the image to 300dpi with a scan gap of 0.085 (~300dpi) and from what I could tell, more detail could be seen on the 300dpi version. So maybe the dot size of my laser cant handle 500dpi?

I think you would have to pay a lot of money for a lens that could resolve 500dpi. But it would be unnecessary, as the
eye doesn't really see that much detail anyway.
I'm not sure what scan gap is, but I do know that dot size is what limits your effective dpi. A spot size of 0.005 resolves
to 200dpi. 0.003 would give you 333dpi. Engraving higher than those numbers means overlapping previous lines, but
not really increasing the resolution.

[Ben Fenton]

Hey Chuck

I'm using scan gap to be the distance in mm (fractions of) the laser dot moves down on each engrave pass. So the lower the number, the closer the lines are.


But yes, Im sure now 500dpi seems like a waste of time. I'll hopefully do a few more tests today to try and work out the dot size : )

[Brian Robison]

I use yellow card stock type paper to test the results of a drawing, sometimes also using scrap black & brass.
It's a lot cheaper than messing up expensive materials...

[Chuck Stone]

Hey Chuck

I'm using scan gap to be the distance in mm (fractions of) the laser dot moves down on each engrave pass. So the lower the number, the closer the lines are.

OK, now 'scan gap' makes sense .. except then I don't know why they would give you both
'scan gap' and 'dpi' to work with, as what you describe as 'scan gap' IS DPI on my machine.
If I choose 300dpi, the puts dots 1/300th of an inch apart along the current line and it moves
1/300th of an inch lower for the next pass.
If they give you both, and the figures don't agree, does it crash? Does it automatically reset
one of the values for you? OR do they use 'scan gap' for one axis and 'dpi' for the other?

ps.. there are reasons to use higher DPI .. it's just that resolution isn't one of them. You may
want heavier engraving or even have a 'second pass' built into the first pass. Higher DPI can
give you a 'stepover' that smooths out the engraving, too.

[Dave Sheldrake]

A laser is not on all the time,(the easy way to look at it) the beam is turned on and off a given number of times in a period, there are two main control systems.

PWM (Pulse Width Modulation) This decides how long in any given period the laser is *on* for.

PRF (Pulse Repetition Frequency) controls how many *times* the laser fires in a given period.

PPI on a western laser is how many times it fires over a known distance, Chinese machines don't have adjustable PPI values (the tubes are DC not RF excited)

The full explanation is a bit more involved but this just about covers it.

DPI is either the resolution of the steppers (the minimum amount they can shift per pulse) or in an image the number of ink dots fired in a given distance.

Scan gap on a Chinese machine is effectively DPI for raster engraving.

hope that makes sense although it is 3:34 am here and I'm rather tired :)

cheers

Dave

[Ben Fenton]

Scan gap, res, ppi, dpi.. Its all good fun ; )

I think i've found the settings i'm happy now. 300dpi seems to be the sweet spot for detail. I suppose what I was trying to ask is whether its best to prepare an image as 500dpi but then engrave it a 300dpi, or prepare it at 300dpi and engrave it at 300dpi. From what I can tell though, it doesnt really make a great deal of difference.

An interesting quirk I've found on laserworks though is on the scan gap interval setting. To set the equivalent of 300dpi, you should use 0.085. However, 0.085 resets to 0.09. Then, 0.084 resets to 0.08, so its either 284dpi or 317dpi. I really doubt it will make any difference what so ever, but I'll prepare some images to those exact dpis and run them through to compare. And then I will know. And then I can stop obsessing over it :D

[Bill Cunningham]

If the manuf. says it can handle 1200 dpi, the it will handle multiples of 300 dpi best. 300,600,1200.. If your working your image at 300 dpi, then engraving at 500 dpi will not give good results. Use 150, 300,or 600.. 300 will probably work best..Some times working at 150, and engraving at 300 works well on glass, so...

[Ben Fenton]

Thanks Bill

So, if I prepare the image to be 300dpi, import that image into the cutting software, which setting should I choose if 300dpi isnt available? On laserworks v5, if you try to set the scan gap to 0.085 (300dpi), it resets to 0.09 which is around 317dpi

[Chuck Stone]

not really sure how to get around that.. can you prep the image at 317dpi? (I don't even know)
I think if you're not using the same or multiples of the same, you may get banding in the
image. (like crossing fresnel lenses)

[Ben Fenton]

Hey

Using photoshop, I suppose you can make an image to whatever dpi you decide, so I'll just do some further testing : )

Out of interest, specifically for clear acrylic, does anyone have an opinion on which software is best out of photograv and 1 touch? I might take the plunge and buy one. Ive been using the demo of 1 touch and seems very good as far as the engravings it produces is concerned

Thanks

[Chuck Stone]

I prefer to do things myself in Photoshop. I'm not a fan of programs that
do everything for you when there are that many variables that need watching.
I tend to do the editing in Photoshop and save it as grayscale. Then print it
out of Corel after converting to bitmap. (I like Corel's bitmap better)

[Bill Cunningham]

For black polished granite/lasersketch marble, Tweak the photo in photopaint/photoshop to what gives you the best results. I usually import the photo into corel, size/resample and position it, then export for photograv processing. Once you get the proper parameters in photograv, it will allow you to process a photo very quickly. I find the generic granite setting works well. I usually put masking on the piece and rub some black ink or stain on it then run the laser at high speed low power just to mark the masking and make sure everything is aligned and looking good. then pull the mask, up the power and go for the real thing.

[Dan Hintz]

I usually put masking on the piece and rub some black ink or stain on it then run the laser at high speed low power just to mark the masking and make sure everything is aligned and looking good. then pull the mask, up the power and go for the real thing.

Use blue painter's tape... marks a bright white with low power and is easily removed.

[Martin Boekers]

But yes, Im sure now 500dpi seems like a waste of time. I'll hopefully do a few more tests today to try and work out the dot size : ) One of the first things I do with a new employee is to have them run tests at different resolution settings, this way they can see the difference... Also I have them run a test on RGB and CMYK as sometimes the difference can be construed as a resolution issue. As others have said always work in multiples and not the numbers between. That goes with photo editing also. I do get work that competition did from time to time that a client wasn't happy with.... Most the times it was because it was run at to low a resolution or appeared to be a CMYK issue. Make sure your happy with the quality of work that you put out and don't cut resolution unless necessary.

[Bill Cunningham]

Use blue painter's tape... marks a bright white with low power and is easily removed.

Ya but wide blue tape is expensive, masking I have, ink I have,(I use the black turtlewax color cure when I can find it) and I get a nice white image through the stained masking (transfer tape)..I use 1" blue tape on small items for a test etch before engraving, but it's too expensive (compared to transfer tape) for larger pieces