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View Full Version : Deep Raster Engraving on Wide Surface Acrylic



Tracey Bakewell
02-26-2007, 9:57 PM
I'm trying to create a template for several brass circles and brass rectangeles. The circles are about 3/4" and the rectangles are about 4" x 3/4". I'm wanting to create these templates on 1/8" clear acrylic. I don't want to vector cut the shapes out rather raster them so they are inset in the acrylic and are flush with the top of the acrylic.

I got the engraver to do the depth but it's not consistent, it actually seems to be forming a ramp from the beginning of the job to the end of the job in the shape.

Here are my settings... I need the 3/4" circles to be .032 deep, and the 4" rectangles to be .063 deep.

Power: 100%
Speed: 24%
PPI: 1000
DPI: 6 (Max)

The circles are pretty good, just need to get rid of the ramp.
The rectangles aren't deep enough with those settings so I tried to run the job twice on the same area, and WOW, no, that did NOT work! Warped the plastic and burned through the beginning, however, since the ramp is there, it started to help get rid of the ramp.

Am I going about this the right way? Do I need two different settings for each depth? How do I stop it from forming a ramp? (I had the same issue with rubber stamps, but wasn't important enough at the time to ask).

Thanks anyone for your help!
Tracey

Dave Jones
02-26-2007, 10:05 PM
Can you describe the "ramp"? Is it top to bottom or left to right? Is it the same in each hole and across the hole, or is it a gentle ramp across the whole width or height of the table?

Tracey Bakewell
02-26-2007, 10:49 PM
Here's a pic of what I'm trying to do. Figured it'd be easier than trying to explain. Unfortunately the "ramp" isn't quite as obvious. The ramp goes from the top of the shape to the bottom of the shape. The top of the shape is deeper and as the engraving progresses toward the bottom of the shape it flattens off, almost like an underground parking garage ramp exit.

The rectangle got ruined when I tried running it a second time. So, before I did that you could probably see the ramp a little bit better than this example because I stopped it about 1/4" down the page when I noticed it was NOT the right thing to be doing.

Does that help???

Joe Pelonio
02-26-2007, 10:56 PM
Is there any reason you can't vector cut it out of thinner material and cement it onto a thicker backing piece?

Consistant depth is problematic when you try to go deep on acyrlic. You might have better luck using ABS, if you don't need it to be clear.

Mike Hood
02-26-2007, 11:22 PM
That's what I'd recommend as well. Layering thin vector-cut pieces onto an uncut sheet would be quick and look better in the end I'd suspect.

Mark Plotkin
02-26-2007, 11:34 PM
Tracy,

Vector cut the shapes, put on a flat piece of stock and shim the outside to the hieght you need with the brass and you will have a perfect templete, shapes and depth! (much faster also)

Gary Hair
02-27-2007, 12:21 AM
How about using a router instead?

Mike Null
02-27-2007, 7:34 AM
I would suggest using a thicker material to prevent warping. When you raster away half the thickness of the template it will certainly warp.

I would recommend at least 1/4" acrylic or better use mdf.

If you use acrylic and try to do the .063" in one pass at your highest dpi you may still get warping due to the heat generated. Two passes at lower dpi may help to prevent warping.

Marvin Sheriff
02-27-2007, 10:19 AM
new to the forum,
another solutin is to use mat board on top of the acrylic. vector out the mat board leaving your acrylic as the backer board. you can lightly vector on the acrylic the outlines of your pieces, place glue or double face tape in the areas between the circles and rectangles.

Marvin Sheriff
LMI SL 3400 100watt

Rodne Gold
02-27-2007, 12:03 PM
In all likelyhood the ramps are caused due to melt and debris not being removed and being "re-engraved" on. The other problem you will face is bad engraved surfaces , very difficult to get it smooth.
If you insist on going that route I would use higher pressure air assist for material removals (and cooling) and do a "polishing" pass , IE a pass at like 100% power and pseed to polish or remelt the badly striated surfaces you will get with deep engraving of acrylic.
One other problem you will face with templates with tight tolerances and flush insertions is getting the stuff out after , I suggest you make a hole in the cavity or a finger lip on the side of each cavity to aid removal.
Why do the brass pieces have to be flush with the top surface abd why does the template have to be acrylic?

Michael Kowalczyk
02-27-2007, 12:54 PM
Tracy,
Is there any reason you need it to be acrylic? I would use the 2 piece method and if you have any type of volume to do I would make to sets so you can set up the 2nd while the first is running. Since it sounds like you will just be rastering/engraving your brass. You can use a 1/2" to 3/4" MDF sheet as your base and then use an 1/8" hardboard or 3mm Russian birch ply as your template. If you need precise shims to maintain your focus, you can try cardboard, sheet metal scraps from local machine shops, laminate samples, thin stock plastics you can cut to size and glue to the base. I would also drill a hole in the base so you can push the brass out if they are snug.

I made an acrylic template using the raster method for some 500-2" round wooden key-chains that were engraved on both sides. It worked but what I described above is how I will do it next time to increase production efficiency. Even though this was a donated project and I had volunteers to run the laser I still want to optimise the process.

Hope this helps,

Tracey Bakewell
02-27-2007, 3:08 PM
Ok, let me kind of explain more of what I need this template for and maybe the answer is in the solution I need...

It is not necessary for it to be clear acrylic, just what I had handy and bought at home depot. I was originally looking for smaller, but this is all they had. I think I could even use ABS or wood for that matter.

I want to be able to set my 3/4" brass circles in the template so they are laying on the laser bed perfectly down a centerline I have in Corel, centered with the small circle opening where the S clip will go. If I don't have a template, I'm not trusting myself to lay it on the laser bed perfectly straight so when it is marked, the words will not appear perfectly centered.

The rectangle is not as important as it's a square object, I just want it in a template so I'm not fussying around with getting it centered with the text and everything will be the same place every time.

These name plates and circles will never have any adhesive backing applied to them, they will be screwed on a leather halter or saddle, or hung from a bridle.

I'm not following how I would vector cut the acrylic. Can someone explain? I can't vector out the entire piece because then I'd loose my little hold I have sticking up to put the circle on to keep the shape centered.

The only reason I want the brass flush with the template's surface is to make focusing easier. I can run an entire job of brass with different shapes and thicknesses, however I'm not set on that, just seemed like a good idea at the time. I'm not following the shim idea just yet.

Anyone want to help clarify some of my sticking points above???

Thansk!
Tracey

Tracey Bakewell
02-27-2007, 3:11 PM
I only have the CO2 laser, no router :(

Tracey Bakewell
02-27-2007, 3:17 PM
I guess I could do that, I couldn't locate anything thinner yesterday when I was out shopping. I'll have to find something smaller from Johnson Plastics probably. My only issue is the small peg I need to be sticking up that shows me the top center of the circle to keep my text centered when lasering.

Vicky Orsini
02-27-2007, 3:24 PM
Tracey, I second what the others have said. Use MDF - way easier to work with.

As for your different depths, I believe ULS has the ability to change the power/speed settings based on colour, right? So, when creating the circle templates, colour them black and set that speed/power to what you want. For the rectangles, change them to another colour (blue, or whatever) and set the power higher/speed slower to give you a deeper raster.

Also, I've found when making templates, a light vector line around the outline of the raster image helps make the piece sit better.

Hope this helps. :)

Vicky Orsini
02-27-2007, 3:26 PM
My only issue is the small peg I need to be sticking up that shows me the top center of the circle to keep my text centered when lasering. If you use MDF, you can raster a mark at the top center to show you where center is. Or, if you have screw holes in your brass, you can raster around those screw holes when you make your template. They'll help hold your piece in place and keep everything centered.

Tracey Bakewell
02-27-2007, 3:36 PM
Vicky, thanks! I actually am doing the latter of what you describe, I am rastering out the entire brass tag leaving the screw hole alone, so that it sticks up like a peg for me to set the brass on top of. Fits perfectly. My main problem is the rastering of the rest of the shape. The base is coming out un-even. I explain further below.

I'm not able to figure out what MDF is though? I've searched Johnson Plastics website and am coming up with plaques? They aparently don't offer any ABS plastics either?

It almost sounds like I need to go with a wood product for a template vs. the acrylic I'm using.

Tracey Bakewell
02-27-2007, 3:38 PM
Vicky, you're right on here as well. I can definitely assign a different color to my different depths... once I figure out what those settings are :)

And you're correct, the vector line around the outline of the image has made the brass fit nicely into the template. Thanks!

Vicky Orsini
02-27-2007, 4:02 PM
It almost sounds like I need to go with a wood product for a template vs. the acrylic I'm using. Definitely! MDF is a wood-based product. Go to Home Depot, they'll be able to show you some. ;)

Vicky Orsini
02-27-2007, 4:04 PM
The base is coming out un-even. If the material is 're-lasering' the debris, as Rodne says, then the MDF will definitely help with this part as well.

James Stokes
02-27-2007, 5:15 PM
Tracy, I do things like this all the time. The easiest way I have found to do it is like this. I start with a new page in Corel, make 2 layers. Bring in your job. Put a hairline vector around the outer edge of your plate. Group every thing and then duplicate and lay it out as you need it. Once this is done ungroup every thing. Then move all of your vector outlines to layer 2. If this is a 1 time project I use a piece of cardboard if it will be an on going project I use plywood or something like that. Turn off the printing of layer 1 and send layer 2 with the vectors to your laser. Run this vector job at a lower power On the cardboard or plywood. Then lay your plates into the outlines. Turn off the printing of layer 2 and send layer 1 with your raster images to the laser. Your job is now ready to run
The best advice I can give any laser owner is to learn how to work with layers. It will make your life much easier.

Dave Jones
02-27-2007, 6:32 PM
For buying sheets of acrylic I'd suggest going to Delvies:

http://www.delviesplastics.com/

They sell cast rather than extruded acrylic. The stuff you buy at home depot is probably extruded. It melts differently than cast.

When I make templates out of acrylic I always vector cut them and then add layers of acrylic if needed, which might have different vectors cut, or just a solid sheet for the base.

Remember that to hold a shape you do not need to have the complete shape. For example, a circle with a couple of smaller circles on the sides where your fingers can fit will still hold a circular tag just like a complete circle. But the extra cutouts allow you to put the discs in and out easilly.

When making the template you can rastor or vector (at a lower power) lines for alignment. For example you could make a line that goes across all of the uncut acrylic from left to right, through the center of all circles, and then individual lines up and down showing the exact top center and bottom center of the circles. You can then use these to rotate the discs so they are oriented correctly.

Mike Null
02-27-2007, 6:57 PM
Hd and Lowes both sell the kind of mdf you need in 2x2' squares as well as 2x4 foot rectangles. 1/4" thickness should be just fine.