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Dan Gochnauer
08-25-2005, 3:46 PM
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
08-25-2005, 3:55 PM
Are you using air assist and are you elevating the pex?

Shaddy Dedmore
08-25-2005, 4:19 PM
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
08-25-2005, 5:39 PM
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
08-25-2005, 6:05 PM
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
08-25-2005, 6:13 PM
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
08-25-2005, 9:10 PM
I use 7 speed and 100 power 1000 fre. on my 35 watt Mini plus air assist. Works just fine
rich

Dan Gochnauer
08-26-2005, 12:54 AM
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
08-26-2005, 5:34 AM
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
08-26-2005, 8:02 AM
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
08-26-2005, 2:11 PM
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
08-26-2005, 5:30 PM
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
01-24-2007, 1:25 PM
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 :D

Mike Ross
01-24-2007, 1:51 PM
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
01-24-2007, 2:19 PM
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.

Vicky Orsini
01-24-2007, 2:54 PM
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? Would you say mask on or mask off would work better for melting? I have some HD acrylic that I've been playing with, and it's not so much the edges that bother me (although those remain tacky for days after I've cut them :confused: ), but rather that the "face" of the material gets swirly, melt-like marks all over it. Would leaving the mask on help this? Or is this a problem with the material itself? Where do you get "good" acrylic without paying an arm and a leg for "laser-specific" stuff?

Lee DeRaud
01-24-2007, 3:14 PM
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 RossWhich ULS? I was under the impression that all of them are already plumbed internally for air assist: the only thing you have to buy is the nozzle cone and the hose adapter to plug your compressor into the back.

Lee DeRaud
01-24-2007, 3:22 PM
Would you say mask on or mask off would work better for melting? I have some HD acrylic that I've been playing with, and it's not so much the edges that bother me (although those remain tacky for days after I've cut them :confused: ), but rather that the "face" of the material gets swirly, melt-like marks all over it. Would leaving the mask on help this? Or is this a problem with the material itself? Where do you get "good" acrylic without paying an arm and a leg for "laser-specific" stuff?The mask material on the HD acrylic is some kind of thin plastic film, like dry-cleaner bag stuff: it should definitely be removed. I've had good luck with the HD acrylic, just using transfer tape (on the bottom side only) to eliminate burn marks from the cutting table.

Todd Schwartz
01-24-2007, 6:13 PM
Vicky - had the same issue with Home Depot's acrylic - had a batch early in my experience that worked well, next batch, same manufacturer and all and I could not get a good result, always the little "swirls". Masking and power / speed adjustments did not help. Spent way too much time trying to get the perfect combination and never found it.

Ended up going to a local plastics distributor and have not had an issue since. Cuts and engraves beautifully - price is $4-$4.50/ft2. But well worth it in the long run.

The other thing I noticed is that I am guessing that the acrylic from HD is extruded. It mic's out to exactly the same along the length of the piece. The cast that I got from my local plastics guy varies up to 15% in thickness, which is a characteristic of cast acrylic.

Todd

Richard Rumancik
01-24-2007, 8:37 PM
Vicky

The swirls are a result of the vapour from the acrylic swirling around on the surface. The laser turns the acrylic to a gas. Ideally it exhausts through the bottom kerf but sometimes the air assist will blow it around and damage the surfaces.

I haven't heard of "laser specific acrylic" - I buy from a GE Plastics outlet or from a Cyro distributor. In some thicknesses I can get paper mask both sides. If you can get it, use it. The polymask is hopeless for lasering. It will weld to the part or else not stick well and cause damage as you see.

If I can only get poly acrylic I have to remove the poly and then apply paper mask.