Cutting Acrylic

[Dan Gochnauer]

I have a 35 W Epilog laser and I'm trying to cut a design out of 1/4" acrylic. I've set my power to 100% and Speed to 1% or so, which cuts through but I get melding, which is not acceptable. Can you give me some tips on how to get a clean cut. I've looked at some interesting work others have done (the acrylic puzzle for instance), but with the melting that I'm experiencing, I would not be able to cut that out. What am I doing wrong? Thanks for your help

[Rodne Gold]

Are you using air assist and are you elevating the pex?

[Shaddy Dedmore]

Have you tried going faster? Might be staying in one place too long and building up heat and re welding. Air assist like Rodney suggested is pretty important (for cooling and for blowing the waste through the cut). You might try lowering your pulse rate also. They say keep it high to get a cleaner looking, smoother surface, but you might not get as much consentrated heat if you lowered it some.

Do you have the mask still on the acrylic? Are you using cast or extruded, or did you just grab some of whatever HD had?

Are your mirrors and lenses clean? How about alignment? If your laser isn't getting it's full power through efficiently, you'd have to slow it down to compensate. Might try a cleaning and check the alignment to see if you could allow your laser to cut at a faster rate.

Can you cut 1/8" stock OK?

EDIT: sorry, I meant speed it up some. And I was saying that if you werent getting the power through, that's why you had to run it at 1% speed. Seems too slow, try speeding it up to 4, 5 or even more. Just slow enough to still cut through.

Shaddy

[Dan Gochnauer]

I do have the piece elevated with a Benecore cutting grid. I set the PPI to max so I haven't tried lowering it. I do not have Air Assist and didn't plan to get that, but maybe that was a mistake. I believe the lenses are clean and the laser is aligned as best as I can tell. I haven't tried cutting 1/8" material. I went to TAP Plastics and got a few lbs of scrap plastic just to experiment with cutting. I'm exploring Architectural model cutting and have no problem cutting wood but needed to explore plastic, since there are more possibilities.

I haven't explored lowering the power, I assumed that I needed full power. Can I still get cutting with lower power? I'm already going about as slow as I can go, but with the melting, I can't use the material I am getting. Right now, I'm just cutting a simple pattern that I can move around the "page" so it doesn't take long to try things. The actual pice will be very extensive and probably will require a long time on the laser. I want to get this right before I start wasting real material. Thanks for your replys. I'll keep trying and see how it goes.

[Rodne Gold]

Air assist is the key - get it or make a diy system , all it is is a directed jet of air at the point of cut , some aquarium tubing , plastic nozzle a small compressor and a flow valve are all thats required.
We do a lot of acrylics for arch models , normally using 1-2mm acrylic and 3mm at the max , we hardly EVER use 1/4" for that. What are you using the 6mm for?

[Lee DeRaud]

I haven't explored lowering the power, I assumed that I needed full power. Can I still get cutting with lower power? I'm already going about as slow as I can go, but with the melting, I can't use the material I am getting.

Sounds like you might want to back the power down to maybe 60% and then experiment with the speed until you get it to cut through. I don't know how the speed settings map between an Epilog and a ULS, but the settings I've got for 0.2" material show 50% power, 0.5% speed, 1000PPI for 35W. (The high pulse rate is what polishes the edges...of course that assumes you're using extruded acrylic.)

FYI I have no problem cutting 0.2" with 75% on a 25W ULS, no air assist.

[rich shepard]

I use 7 speed and 100 power 1000 fre. on my 35 watt Mini plus air assist. Works just fine
rich

[Dan Gochnauer]

I've played around some and determined that I needed to adjust the focus some. Still getting a little melting, but not as bad as I was earlier. I'm still not happy with the results. I think I'm going to look into air assist. I'm interested in the DIY version. I can understand most of the concept, but would like some idea of what type of compressor I need. Can I use a air brush type compressor? I also would like some idea of the PSI that I need and if I should expect to adjust the PSI for different materials. Since I've never seen a professioonal setup, I know I need to get enough plastic hosing to reach the max XY but still keep the hose from dragging. Any suggestions there?


I have a Epilog Summit that has two different lenses. I've tried both, one gets much finer cut, but I have more difficulty getting inside pieces loose. The other lense gives me a wider "kerf" but the melting seems more severe. I'm using 600 DPI and I've played with the "Rate" (I assume PPI). Higher rate gives a smoother finish. I've set the rate low (10%) but that didn't seem to make much difference than doing the cut at rate = 80%.

As for what I'm trying to do, I'm attempting to produce a mold for some 1/2" scale molding for a building. The molding has a complex profile, so by cutting 20 pieces and putting them together, I will have a long enough mold to pour resin in to get the resulting molding. Normally I don't cut material this thick, but I don't really want to cut 40 pieces, but maybe that would be an alternative. This is an area that I plan to do more of, so investing in air assist (expecially when I have a air brush compressor already) doesn't seem to far out.

Thanks for your help.

[Rodne Gold]

I'll start off last , cutting the profiles to give you a mould will not produce great results , its unlikely that your pieces would be cut perfectly perpendicuar to the surface and thus the mould surface will have "ridges" (If im understanding you correctly) - The laser beam diverges somewhat and thus thicker stuff tends to NOT have perfect straight down cuts. The lens that gives you the bigger kerf is the better lens to use as it has a larger depth of focus and diverges less than the other one , it would even be better to cut 40 3mm sections than 20 6mm as the sides of the 40 would be straighter. Worse than this , if you use CAST acrylic , the thicknesses of the sheets vary a huge amount more than extruded which doesnt vary at all in effect. You might find one profile section varying by as much as + and - 10-15% on cast!!!
You will have to do some finishing on the master you are making for the mould.
You could do the profile in wax and use RTV to cast it?
A small 1-2 hp compressor - oil free will do , you dont have to maintain more than 20 psi , a bit of clear aquarium tubing , most likely 6mm at most with a small nozzle - use a cable tie to position it so it directs air at the cut , route the tubing so it doesnt interfere with the motion system or put resistance on it , get a water trap and a variable pressure valve , most likely available from the compressor guys. you can have a fairly small orifice at the nozzle , the air assist only needs to be directed at a small area.

[Jeff DeVore]

In my Epilog Legend manual for a 30-35W laser it gives the settings of 12% speed - 100% power with 4500 frequency for 1/4" acrylic.

[Dan Gochnauer]

I'll start off last , cutting the profiles to give you a mould will not produce great results , its unlikely that your pieces would be cut perfectly perpendicuar to the surface and thus the mould surface will have "ridges" (If im understanding you correctly) - The laser beam diverges somewhat and thus thicker stuff tends to NOT have perfect straight down cuts. The lens that gives you the bigger kerf is the better lens to use as it has a larger depth of focus and diverges less than the other one , it would even be better to cut 40 3mm sections than 20 6mm as the sides of the 40 would be straighter. Worse than this , if you use CAST acrylic , the thicknesses of the sheets vary a huge amount more than extruded which doesnt vary at all in effect. You might find one profile section varying by as much as + and - 10-15% on cast!!!
You will have to do some finishing on the master you are making for the mould.
You could do the profile in wax and use RTV to cast it?

Thanks Rodne, great thoughts. I've been playing around with this concept and I understand what you are saying. I just attempted to cut balsa wood rather than plastic, since it seemed to cut reasonably well. However, it started burning as I got to the 6th profile. Not a good plan. I'm sure air assist would eleviate that problem. Looks like I'll need to explore the DIY air assist thoughts you had. Doesn't seem too hard, hope it doesn't blow the piece right off the board. Do you need to tack it down?

I've thought about doing a clay profile, but getting it straight is extremely difficult. I do know about RTV rubber and I plan to use it but this was a thought I had to explore getting the proper profile and making it long enough to be useful.

Maybe I'll try cutting 40 1/8" pieces and see if I can not burn them up.

Thanks

[George M. Perzel]

Hi Dan;
Quit screwing around and get the compressor as Rodne suggested-you'll find you will use it for everyuthing and it will make your life much easier. Good Luck
George

[Matthew Sullivan]

I recently encountered this problem haha. I was using my compressor that I had hooked up to my laser for airbrushing, then when I attatched it back to my laser I forgot to turn it on ( the compressor and blower are on the same switch ) so when I flicked the switch only the blower came on. So I had a lot of melting on the top of the acrylic and it would only cut a little way through. I thought I had broken something. So I took apart my laser carrage and I had a REALLY dirty lens, then it clued in to me that I must have had no air assist on. So the melting was because of a dirty lens, which was inturn because of no air assist. So I cleaned my lens's and mirrors, turned my compressor on, and all was ok again

[Mike Ross]

I have a 25W Uls with no air assist and would really love to see some pictures and options of somebodys DIY (or factory) air assist. Would like to see how the tubing and nozzle is attached and arranged so that it follows the cut and stays out of the way of the motion system.

Thank you,

Mike Ross

[Joe Pelonio]

Can I use a air brush type compressor? I also would like some idea of the PSI that I need and if I should expect to adjust the PSI for different materials.

I have a Epilog Summit that has two different lenses. I've tried both, one gets much finer cut, but I have more difficulty getting inside pieces loose.

An airbrush compressor that puts out at least 20 lbs while running through the 1/4" tubing and any nozzle you would use will be fine. The one I use for most work was under $100 and keeps it at 25lbs.

If your cutting results in parts being hard to get loose, try a second pass at faster speed and lower power, maybe in your case speed 50 power 50. It's just to clear out any rewelding or perforation at the bottom edge and won't take long.