Converting programs for Engraving Manual Method and Adobe Photoshop [Archive]

Frank Corker

08-28-2008, 7:22 AM

Okay a lot of people have been saying the difficulties of using Photograv and have been shown the manual method using Adobe Photoshop.

Now Rodney Gold who is one of the moderators and guru from this site, conceived a method of using Photoshop and manual settings. The method gives a remarkably similar result and I quite often use it more than Photograv. Unfortunately either not many people wrote it down, don't know about it or have got confused trying to do it or they cannot be bothered because it is quite a long process. Rodney has already suggested in another post that we get together to try and make a fast method. I think I have created this solution. Read on.

Attached there is a zipped file. Extract it and inside you will find another file appropriately named The Gold Method.exe (that one's for you Rodney). Double click on it and please read the instructions, especially the beginning where it will extract the file to.

If you are using Adobe Photoshop CS3, it is a no brainer. If you are just using Adobe Photoshop then you will have to extract the contained file to this location:

C:\Program Files\Adobe\Adobe Photoshop\Presets\Actions

This will be the location of your preset action folder, if you still get it wrong then manually copy them over.

Okay there is a feature in Adobe which is seldom used called 'ACTIONS'. By activating one of these actions it will automatically allow you to convert any picture, colour or otherwise into a suitable engraving ready image in seconds, using Rodney's tried and tested method, but without any input from you other than pressing a button. (Anybody have a problem pressing buttons??????)

I have made actions for the following processes;

300dpi positive
400dpi positive
600dpi positive

300dpi negative
400dpi negative
600dpi negative On the negative ones, I have flipped the image as I was thinking about reverse engraving when I created them. If you are not reverse engraving (i.e. a mirror) then just click flip horizontal. It must be done in Photoshop before you save it.

Here are a couple of things you need to do. SIZE YOUR IMAGE FIRST (8"x10" etc) and then save it. Then run The Gold Method.

The installation will only ever need to be done the once.

Please don't be a lurker, if you try it, post your thoughts or suggestions so that we can look at them again or if it works for you, let's hear that also. We try to help one another so please make the effort.

martin g. boekers

08-28-2008, 7:50 AM

Frank,
I tried to download your zip file, but then it logged me off the forum?:confused:

Any idea what happened?

I tried this a couple times with the same result.

Thanks,

Marty

Frank Corker

08-28-2008, 7:59 AM

It shouldn't have done that Martin. PM me your email address.

Scott Shepherd

08-28-2008, 8:19 AM

Does it work with Photoshop Elements Frank? I don't see an "Action" folder in my Presets folder.

I'm guessing no?

Mike Null

08-28-2008, 8:27 AM

Frank

Any chance you can set this up for Photopaint?

Darren Null

08-28-2008, 8:39 AM

Heh. "The Gold Method". Sounds like a pyramid sales outfit.
=8-)

Thanks for making that action Frank. I was going to do it, but my roundtoit got delayed at customs.

Doug Griffith

08-28-2008, 8:40 AM

Hi Frank,
Whats in the executable? I'd like to try this out but am a Mac user. Can you compress the actions/directions into a zip?

Also, there is an even less used feature in Photoshop (and Illustrator) where scripts can be ran. See http://www.adobe.com/devnet/photoshop/scripting This may be a better way to go than actions. Not sure.

I've got quite a bit of experience in this and can help if needed.

Cheers,
Doug

matt heinzel

08-28-2008, 9:51 AM

Wow great! I ran the script with great results! I haven't engraved anything yet, but so far so good!

Frank Corker

08-28-2008, 10:18 AM

Well things are looking pretty positive then. This is the original script that Rodney came up with. The actions are just a way of doing it automatically without having to give it much thought.

1) Convert to 8 bit greyscale (image/mode/greyscale)
2) Resize the image to the size its gonna get engraved using 150-300 ppi (150 for less detail)
(image/image size)
3) Bump up contrast and brightness about +25 in
both cases - you dont want the pic to be insipid areas of medium grey. (image/adjusyments/brightess-contrast)
4) Heres the VITAL part - use unsharp mask at 500% and a radius of 3-5 pixels - threshold 0 - this will exaggerate edges radically , but thats what you need. In fact you can do this and then STILL add another unsharp mask at 150 % , 1pixel and 0 threshold AFTER the 1st unsharp if you want even more edge detection
(filter/sharpuen/unsharp mask)
5) Convert to a bitmap using 125-150ppi and a diffusion pattern. (image/mode/bitmap)
5) laser.

That is basically all that is in the actions script, except that when you do it manually it takes a few minutes, using this it takes about 30 seconds. The way I have configured it even removes the requirement to choose the correct dpi settings and get the positive and negative issued dealt with.

I'm sorry for those of you who have Elements and Photopaint, I don't have them on my computer so not too aware of what's available. I'm sure that someone will be able to sort out something similar for other programs.

Darren Null

08-28-2008, 10:20 AM

Whats in the executable?
It's a self-extracting archive that (hopefully) puts the files in the right place automatically.

Attached is a zip with just the action file and instructions. So you have to put the files where they should be manually.

Doug Griffith

08-28-2008, 12:15 PM

Thanks a bunch.

On a Mac the path is:
/Applications/Adobe Photoshop CS3/Presets/Actions/Commands.atn

David Dustin

08-28-2008, 12:34 PM

Thank you soo much, I was ready to buy photgrav and was wondering why there wasn't a good equivilant in Photoshop.

Because of my other business (crash animations) we use photo shop as much as 3ds Max (the best animation software in the world, but I am biased).

On another note: has anyone ever tried using Normal maps for engraving?
Normal maps are used a lot in video games and 3d work to give fake displacement and to show texture.

Thanks,
David
EDIT: I just tested the action on PS CS and it worked perfect!

R. A. Mitchell

08-28-2008, 2:13 PM

Frank,

I don't know what I was doing wrong with the manual instructions before, but your actions piece seems to have straightened me out. This has been the most helpful piece of advice from this forum yet.

Thank you!

Rob

Frank Corker

08-28-2008, 2:35 PM

That's great news! This is why we all have to stick together.

martin g. boekers

08-28-2008, 8:09 PM

Programs like Photograv, and actions in Photoshop making lasering images easier. It may not always be the best way, but it is the easiest!

What needs to be understood if you want to laser great images is to truly understand the halftone process. Halftones are what you see in everyday images a series of dots of different sizes to give the effect of highlights, shadows and the gradation between them.

With a magnifier and a newspaper you will be able to see the relationship between the dots and the image.

The problem lies within the substrates, is resolution, power & speed settings in coming up with the best compromise in converting to a halftone as different substrates burn at different rates and depths.

Programs like Photograv and the Photoshop action, tend to exagerate the image by increasing the contrast at the edges of the image. Which makes it easier to produce an exceptable image quickly.

If you have Photoshop open an image and under the filter section you will see one called "find edges" try it, you'll see how it over defines the edges. You can vary it by fading the filter (under Edit) or if you have a duplicate layer (not filtered) under it vary the opacity. This will show how you can work with the find edges filter. I use some form of this process every once in a while. It a good tool for some projects. This won't make the perfect picture, but it will help in understanding part of the steps that a program like Photograv uses.

Here is a web page that will explain some of the halftone process using plastic.

http://www.rowmark.com/mark/laser_guide/pages/Photo.asp

I you do some research on halftones you may find your answers without purchasing a program.

Hope this helps,

Marty

Darren Null

08-28-2008, 8:48 PM

Normal maps? I seek enlightenment, O guru. <--not sarcasm- I'm not good at 3D
Oh yeah. Halftones. This is a process where you only have black to work with (as we do) and you use different-sized dots to make up the image. If you use the 'halftone' filter in any program you like; you're probably going to end up with an image that looks like it came from an 80s newspaper. Nevertheless, what we do is halftoning, but with a different emphasis these days...for lasering, all the dots are the same size and it's the _distribution_ of all these identically-sized dots that make the picture.
I'd recommend having a click on the link above, because it's useful information

Darren Null

08-28-2008, 9:32 PM

Halrighty. Test time.
We have:
1) original
2) etchtone (photoshop filter- poor man's photograv...couldn't be arsed to fire up photograv and photoshop was already open)
3) halftone. You will notice that there's all sorts of grey in there. I haven't found a halftone filter that just deals with black and white, although there undoubtedly is one.

10 centimos says that number 2 gives you the best burn, whatever it looks like on your screen. Any takers?
EDIT: And if you run #3, you'll have to run it through another filter to get it right.
EDIT AGAIN: Oh cock. I got the size of the etchtoned picture (#2) wrong and it's smaller than the other two. It'll still burn better, but it's not scientific anymore. Damn. Frottage. Etc. Long evening.
EDIT AGAIN AGAIN: Resized 'em all. That's better. We have SCIENCE! again.
EDIT AGAIN AGAIN AGAIN: No we don't. It's still bloody smaller. Hmmm. Science will have to wait till tomorrow, methinks. It'll still be a better burn than the other 2 though. Try it.

R. A. Mitchell

08-28-2008, 10:16 PM

I tried the "Gold" action with two different pictures. Neither of them gave me great results on the laser. However, that's not the point.

For a newbie, figuring out what a picture needs to look like on screen before sending it to a laser is 75% of the battle, and Frank's Photoshop application got me at least 80% of the way there. And then there's the material being engraved. I tried a pretty good picture on finished an unfinished wood. I was surprised by how much better the imaged looked on the unfinished wood. The finished wood gave an unexpected effect - the areas that burned deep looked good, but the lightly burned areas were brighter than the natural wood - probably because the laser didn't actually burn wood, but instead altered the finish. The lighter areas threw off the shading for the entire image.

All of this is to say it takes a lot of practice and experience to laser images reliably. I'm greatful to guys like Frank, though, who help speed the process along.

martin g. boekers

08-28-2008, 10:21 PM

There are a variety of halftone digital screening techniques out there. The ones that Photograv uses is a stochastic half tone. And like you said it uses the same size dots.

Before getting into lasering I was a photographic printer, an old days type enlargers and chemistry and darkrooms! (boy I am old!).
I did most the printing and didn't deal too much with the scanner guys, they where a whole different breed. (now I wish I paid a bit more attention!)

These guys really worked their magic in getting quality work to the presses.

I can understand that if you have dots all the same size and they happen to be the same diameter as your lens resolution. It makes life easy on the laser as long as your exactly in focus across the board and consistant on the burn.

I can see issues arising as different substrates such as wood or plastic that there would be more "afterburn" as the laser "dots" the material as opposed to laser brass metal or marble. (take a cigarette for example and touch it to paper, the paper burns after the cigarette is removed) So now that dot is a bit bigger.

I'm not sure why if I created a screened halftone and the the none of the dots are smaller than the diameter of the lens that it wouldn't work. I burn line art all the time and isn't that really what a screened image is? (black & white)

I'm sorry if I sounded like a "know it all" because believe me I don't!
I just wanted to share a different side of imaging that some in the forum may not have experienced.

One thing that has confused me is if Photograv uses the same size dots, why do they tell you not to rotate the "engraved file"? If you run your laser at a slower speed to make the x and y planes more similar why would rotating the file before you burn it make a difference?

Can we address the laser through a profile like you can with a color printer?

Someday maybe there will be more profiles that we can add and modify.
I guess there are a few options now as you can pick in the drive photo or clip art. Wouldn't it be great just to check in the drive Photo wood, photo marble etc.

I know I had a problem awhile back on one laser because of that. I run a dye sub printer off the same computer as that laser and somehow the defaults got changed and it converted my file to the dye sub profile when it was sent to the laser, that created a big headache until I discovered it!

I want to do more images and I'd like to understand how to have more control on their outcome with less waste and testing. I'll keep plugging away at these conversions as I find time, but for now I to use Photograv because it's quick and easy.

I really do appreciate this forum as we all have different experiences in what we do and it's great to have this forum to share it with others.

Darren Null

08-28-2008, 10:37 PM

I can see issues arising as different substrates such as wood or plastic that there would be more "afterburn" as the laser "dots" the material as opposed to laser brass metal or marble. (take a cigarette for example and touch it to paper, the paper burns after the cigarette is removed) So now that dot is a bit bigger.
And there you have put your finger on the nub of the matter (-1 point to me for mixing metaphors). Making papers, it's essentially an instantaneous operation. *THWOCK* and the page is done. With lasers, to make bigger dots, you have to apply heat to a small area for longer; and even if it doesn't catch fire, it's going to look different than (to?) the smaller dots. Blacker, maybe.
With photograv, all the dots are the same size, so all the black areas are treated the same and should look the same. The exception, of course, is where you have a lot of black together and adjoining pixels will be getting the heat from their neighbours.

I'd quite like to see a halftone filter that deals with just black and white. All the ones I've seen are 8-bit greyscale. With lasers, you burn a hole or you don't.

if Photograv uses the same size dots, why do they tell you not to rotate the "engraved file"?
I have no idea. Anyone know?

Lee DeRaud

08-28-2008, 11:22 PM

Well things are looking pretty positive then. This is the original script that Rodney came up with. The actions are just a way of doing it automatically without having to give it much thought.

1) Convert to 8 bit greyscale (image/mode/greyscale)
2) Resize the image to the size its gonna get engraved using 150-300 ppi (150 for less detail)
(image/image size)
3) Bump up contrast and brightness about +25 in
both cases - you dont want the pic to be insipid areas of medium grey. (image/adjusyments/brightess-contrast)
4) Heres the VITAL part - use unsharp mask at 500% and a radius of 3-5 pixels - threshold 0 - this will exaggerate edges radically , but thats what you need. In fact you can do this and then STILL add another unsharp mask at 150 % , 1pixel and 0 threshold AFTER the 1st unsharp if you want even more edge detection
(filter/sharpuen/unsharp mask)
5) Convert to a bitmap using 125-150ppi and a diffusion pattern. (image/mode/bitmap)
5) laser.If you're working with a "negative" medium (e.g. black granite), what's the optimal point in this sequence to do the invert?

I don't have any Photoshop (except maybe the freebie version that came with one of my cameras), but I'm going to take a look at the API for PhotoPaint and see if I can cobble up a VBA script for some or all of it.

martin g. boekers

08-28-2008, 11:22 PM

One more thing to try, instead of using the "filter" halftone effect,
open an image in photoshop, convert to 8 bit grey scale, now under the image dialog box pick the bitmap option. This should open up a dialog box that deals with halftones and dithering. It gives you a few options, you can even use custom screens!

When I get a chance I'll play with this a bit and post results. If someone tries
this let us know your results!

Thanks,

Marty

Darren Null

08-28-2008, 11:28 PM

If you're working with a "negative" medium (e.g. black granite), what's the optimal point in this sequence to do the invert?
After it's converted to 1-bit.

When I get a chance I'll play with this a bit and post results.
If you try it, can you use the 'original' eyes photo? I'll photograv that too, and we can have a real test.

Done. Attached is a GIF representation that's pretty accurate. BMP in the zip file for purists, but it looks the same. I swapped to GIF because the filesize is smaller because there's only 2 colours (30-odd K plays a 200K JPEG for the same image).

Yup, it looks sucky on screen, but the image below will give the best results if you burn it.

Carrol Fleming

08-29-2008, 1:10 AM

I managed to get everything working and ran a trial. I had actually been fiddling with photos today so had another piece I had done with pictures I had worked on in CorelDraw.

The top two pictures are done in CorelDraw using the following method:
Effects - Adjust - Desaturate (converts to greyscale).
Effects - Adjust - Hue/Saturation/Lightnesses - set saturation to -100.

With the picture on the left I then adjusted the brightness of the picture.

Using the Gold Method, the bottom two pictures, I did not make any further adjustments to either of the pictures so the picture on the left is a bit dark. The wood used in the Gold method is also slightly darker.

Basically I would definitely try the Gold method first before going through the hassle of fiddling around. I had tried the step by step Gold method before but had shelved it for a "free time day" which finally arrived!!

Thanks Rodney and Frank
Carrol

Rodne Gold

08-29-2008, 1:37 AM

The method i posted is a "cheap mans" version of photograv , kudos to Frank for formalizing it in an action.
Results using it are going to be variable as some of the steps I proposed will not work 100% on all pics , I have tried various images both ways and some are better with photograv and some better with the photoshop method.
Key to using any of these methods is the original artwork and what it looks like in greyscale after the colour has been removed. If the pic is insipid and does not have a big dynamic range , ie is mostly greyish , you aint gonna get great results.
At the end of it all , there are sooooo many variables that are going to determine your results , is the pic in focus , is it decent resolution , does it have defined edges , what laser power , what spot size , does it need contrast enhancement , does it need the unsharp mask , what materials , how deep must it be lasered and so forth.
Even photograv , albeit it does have variables you can set , is not always guaranteed to work either.
But at any rate , all thanks to Frank for his sterling efforts and for subscribing to the spirit of sharing that makes the internet great ............
Problem for a lot of us is that we dont have Photoshop , so I was fiddling in Corel for a similar type of "action/script" but havent had a lot of success but will continue working on it.
My problem is that we don't do a lot of giftwork , so transferring pics to items is not a priority , but we do however use these methods BIG time for vector clipart (avoids hiden lines , fade islands etc) and often use it for once off quick and dirty engravings of bitmap colour logos we get from various companys.
I have actually also been fiddling with my lasers inbuilt photo engraving thingy (Laserpro.Gcc) and to be "frank" , so to speak (sorry couldn't resist) its very very good (latest spirit driver)

Brian Robison

08-29-2008, 7:39 AM

I for one can't thank Rodney enough. I use his method on a daily basis. I'd like to take off my hat to Frank for doing the works also.
However, as a side note, I shorten the steps myself by not leaving Corel Draw. I've tested Rodney's method both ways and can't see the advantage to going into PhotoPaint. I know the steps by heart and have for probably a year or more. Takes only a minute or two.
I change a lot of Vector art into a bitmap before lasering.
These are the modified steps.
(1) Choose the image and convert to grayscale 300dpi.
(2) Under Bitmap, resample to the proper size.
(3) Under Effects / Adjust/ Brightness, Contrast, Intensity bump up Brightness 25, Contrast 25, Intensity 0 (these setting will stay after you do them the first time)
(4) Under Bitmaps / Sharpen / Unsharp Mask / percentage 500. Radius 2.

I know it's almost exactly the same but I don't have to launch into Photo Paint to do it this way.

Thanks again to Rodney!

I've compared a photo done with the new Epilog drivers Stucki, Floyd, blah blah blah and " The Gold Technique" blows them away!

Frank Corker

08-29-2008, 7:52 AM

The Gold Method most definitely will work with a very high percentage success rate. I think the skill comes in choosing the level of brightness for the picture you intend to engrave. Before running the actions in photoshop, level out the settings and save, after that it should come into it's own.

Earlier in this discussion the halftone effects were being mentioned, on granite I actually like that effect, especially if the engraving is done on a larger piece of granite. It seems to ward off collections of dirt in the final product and less active to grease from the fingers. For something that needs to be seen close up, then it needs to be refined in one of the normal methods (photograv etc), but from a distance I think halftoning. It's just so mind boggling that to achieve that goal.

All said and done, generally the format is, quality picture - quality result.

I'd also like to say thanks to everyone for participating, the wealth of experience that we all have, collectively is amazing. Mmmmm sounds Star Treky!

Dee Gallo

08-29-2008, 9:19 PM

Well, Frank, I sort of got to use your automatic action... I am running a Mac. So, I copied the steps and ran the recording thingy and voila! It worked very well on the Mac!

Even though it loaded onto my pc with Photoshop 7, it wouldn't run, so I'll try to do it manually there too.

What a timesaver! Seconds instead of minutes, but better yet, no brains required... great for us geezers who shouldn't overstrain what little we have left. Thanks for pointing out the action command! I've used Photoshop since the first version, knew "actions" existed but never bothered to play with it.

Of course, until I got a laser, I never had a need to repeat actions exactly according to a formula.

cheers, dee

martin g. boekers

08-30-2008, 11:26 AM

Great!
It's good to see everyone teaming together for the good of the group!
There are so many people out there with different exprience and to have them step up to the plate really makes a difference.

Engraving photographs is one of the hardest things for an engraver to, and now with the help of Frank, Rodne and all the others we all have a better understanding of the process.

No system will be perfect, but now we tremendously increased the odds of
making a quality engraving! Way to go guys!!!!

For those with photoshop here are a couple sites that have actions to download. There are tons of them out there as well as tutorials for making better grey scale conversions.

What I find helps in working towards better images is, when you have an image that you think burns real well, save that image and use it as a bench mark when converting other images. It's nice to have a visual reminder while you are converting.

http://www.atncentral.com/download.htm

http://www.russellbrown.com/tips_tech.html

http://www.thelightsrightstudio.com/photoshop-tools.htm

For those of you that don't have Photoshop or a photo manipulation program there is an open source program out there for free, yes free! That I have heard good things about. I run Photoshop so I haven't tried this out, but I thought I'd pass it on in case there is some interest.

http://www.gimp.org/

Keep up the good work Creeker's

Marty

Richard McMahon

09-03-2008, 10:03 AM

Hey Darren,
It says in the Photograv manual that the converted file is a binary file and these types of files don't like to be manipulated or you lose the subject clarity (or something like that).
Rich.

Richard McMahon

09-03-2008, 8:17 PM

Great thread guys,
One thing I noticed with some old scanned photos is that they have a patterned effect from the texture of the photographic paper, like a honeycomb ,so just to add to the process I use a slight Gaussian blur of about 2-5 pixels until the pattern has mostly disappeared. Do this before the Filter - Sharpen process.
They tend to come out really good but now I just have to set up my laser to engrave them properly.
Also you can play around with the Graphic Pen filter (Filter - Sketch - Graphic Pen) to blend a lot of the small edges to straight lines. Play with the sliders on the right hand side to get the effect you want. It just adds another dimension to the photo when engraved.
:-)

Darren Null

09-03-2008, 10:24 PM

It says in the Photograv manual that the converted file is a binary file and these types of files don't like to be manipulated or you lose the subject clarity
Ah, thanks. In theory rotating an image SHOULDN'T make any difference at all...you're just lining up (say) an 800x600 grid of square dots and turning them into a 600x800 grid, but with all the dots in the same place. I suppose different programs do tricky stuff on the way round.

JPG files, you have to save the rotated file, so you're adding another layer of lossy JPG compression, but for a 1-bit BMP it shouldn't make a difference.

Bob Davis

09-05-2008, 5:04 AM

Rodne/Frank,

Love your work...Excellent.

David Dustin

09-06-2008, 8:49 AM

Normal maps? I seek enlightenment, O guru. <--not sarcasm- I'm not good at 3D

Normal maps are used in 3d applications to fake depth.
Here are 2 images. The top one is a section of tread, the bottom is a normal map. A normal map is applied in addition to the image and it gives a great illusion of depth. A "bump map" can be used as well, where the image is grey scale, but normals are the best.

Consider yourself enlightened o-lasah-hoppa....

http://www.dustinproductions.com/wip/Dolly-tread4.jpg

http://www.dustinproductions.com/wip/Dolly-tread4-normal.jpg

Darren Null

09-12-2008, 8:38 PM

Thank you.
I shall choose to believe that "lasah-hoppa" is a seeker of knowledge.

Neal Schlee

09-13-2008, 4:11 PM

[quote=Brian Robison;916156]
However, as a side note, I shorten the steps myself by not leaving Corel Draw. I've tested Rodney's method both ways and can't see the advantage to going into PhotoPaint. I know the steps by heart and have for probably a year or more. Takes only a minute or two.
I change a lot of Vector art into a bitmap before lasering.
These are the modified steps.
(1) Choose the image and convert to grayscale 300dpi.
(2) Under Bitmap, resample to the proper size.
(3) Under Effects / Adjust/ Brightness, Contrast, Intensity bump up Brightness 25, Contrast 25, Intensity 0 (these setting will stay after you do them the first time)
(4) Under Bitmaps / Sharpen / Unsharp Mask / percentage 500. Radius 2.
quote]

Another step I use is:
(5) Under Bitmaps / Mode / Black & White use a dithered pattern and preview to adjust intensity as needed.

I also sometimes adjust (3) Brightness and Contrast settings to suit photo.

Using these steps I get nearly identical results as Photgrav 2.1, as Brian stated, without leaving CorelDraw.

Thanks to all involved!

Neal
Lasertech Alaska

David Dustin

09-13-2008, 8:53 PM

I have been working on trying to get photographs to lase for a few days now and have not gotten anything good at all (seems like I am on a roll).

My images even when using the "gold method" and variations of the "gold method" yield quite indistiguishable lased parts. As far as being able to maek some of the high quality lased photographs seen around on different sites, it feels like they are out of reach.

it is almost like taking a high level class but having missed the first semester.

My images look good on wood, OK on aluminum but on acrylic it looks like (insert bad word here). I am using 1/4" plexiglass.

Thanks,
David

Bill Cunningham

09-13-2008, 9:24 PM

I used practically the same settings for plexiglass (acrylic) that I use on glass photographs size as needed, re-sample the 8 bit photo to 150 dpi, and convert to binary using what ever. I etch in reverse at 300 dpi 40-60% speed 100% power.. remember, your image must be a negative image because glass and plexi get their contrast from what ever is behind
Below is a rough etch in extruded acrylic.. Normally you would remove the background by making it pure black before converting to binary. Once you invert it to a negative image, the back ground becomes white, and the laser ignores it.. If the photo engraves in wood ok, then it should also work in glass if the dpi is low enough (you don't etch photos in glass with 600 dpi..) ths one was done with the cherry setting in photograv (the old one)

http://www.sawmillcreek.org/attachment.php?attachmentid=96400&d=1220830447

Doug Griffith

09-13-2008, 9:25 PM

Is it possible your plexi is extruded instead of cast? It makes a difference.

David Dustin

09-13-2008, 10:03 PM

And the newbie asks...
How do I know the differerence?

David

Doug Griffith

09-14-2008, 10:05 AM

From my understanding:
1) If it's not clear, it's most likely cast.
2) Cast is stronger than extruded.
3) Extruded may have very fine extrusion lines if looked at through lupe.
4) Lasering extruded stinks more than cast.
5) Extruded is cheaper.

Lee DeRaud

09-14-2008, 10:31 AM

Scott Shepherd

09-14-2008, 10:33 AM

When you laser the clear cast, it will "frost up" and look like etched glass. When you laser extruded, it won't. If you bought it from a hardware store, it's more than likely extruded and the wrong product for doing that.

However, you can take a can of spray paint, paint the backside and laser through the paint, and you'll end up with a nice product. Just use a fast drying paint like Krylon, Krylon Fusion, or Krylon H20 (some Rustoleum paints take hours to dry).

Hehe....Lee beat me to the borg comment ;)

David Dustin

09-14-2008, 11:46 AM

Dang, It looks like I have extruded then...

I'll try painting the back of it then lasing through it.

I tried black marble with the gold method and it works great, just had to make sure my image was at the same DPI setting I was lasing at (yeah I know, Iknow... obvious) and had to reduce the power settings.

Thanks for all your help.

David

Frank Corker

09-14-2008, 12:20 PM

You'll know straight away generally if you have extruded or cast. Cast leaves a beautiful white engraving, perfect for the laser engraver, extruded is virtually clear and appears to melt the surface. The picture that Bill posted, had it been done on cast it would have looked fantastic. Of course as already mentioned, the smell. Cast acrylic has an almost sweet smell to it (gets too much if that is all you are working with) and extruded..... that just stinks the place up, it's horrid. They use extruded over here in the UK to make registration plates on vehicles, it's much more robust and doesn't splinter the way that cast does.

David Dustin

09-14-2008, 2:23 PM

Is there a good source for Cast acrylic in the states?

I ordered what I have from johnson plastics.

Thanks,
David

Neal Schlee

09-14-2008, 3:35 PM

Plexiglas® G is their cast designation, Lucite® L is their cast (Lucite L states right on the protective paper that it's cast).
Plexiglas® MC is there version of extruded, some people mistake it for cast because of the "C" in the code.
Cast is harder, more scratch resistant, less flexible and generally more expensive. Because it's harder it has less tendency to melt when cutting and engraving and it polishes better.

Of course there are other mfgr's, buy from a knowledgable plastics supplier that knows the difference. I see now that Grainger is selling cast sheet acrylic, although it is drop shipped from their supplier. Pricing seems reasonable, $105 for a .118" thick 4' x 8' sheet of clear.

Attached is a pic of a 2.75" x .250" Plexi G ornament. We engraved & cut 400 of these yesterday on a ULS X2-660 120 watt Superspeed® system. The Superspeed is a real time saver on acrylic. :)
A 1.5" FL lense was used.

Neal
Lasertech Alaska