help Cutting 1/2" cast acrylic,

[Chad Fitzgerald]

Im new to the forum, from what I see this is a good place for advice. I consider my self to be a newbee with the laser, had it about a year and a half, have gotten pretty good but have alot to learn. GCC Laser pro spirit 40W.
Her is what i need advice with.
Had a new possible customer ask me to cut 1/2" cast acrylic, clear, he is looking to sub out the pieces as he now cuts them on a cnc but has to polish the edges clear after. He is hoping a laser will cut them clean and clear. Talking with him, if i can do it it would be 100 pieces per order, 6-10 orders per year. 2" x4 1/2" funny shaped pieces. It would be good for me.
Spent yesterday working on the settings, laser cuts through just fine, trying to get it tuned in.
So far the best settings I found is .1 speed, 30 power, 1000ppi, and i moved the table up .070" into the piece.
I have the lens that comes with it, 2"
With this I am getting a pretty good result however, and this is hard to explain so bear with me. Watching the laser cut ther is a "wave effect" as the beam cuts. the bottom of the cut lags behind the top of the cut. I assume this is due to the thickness of the acrylic. I can speed up but the lag gets worse which causes the corners to not cut well.
I would like to speed up to keep cost reasonable. Can I?? Different lens, focus closer??? Any other opinions or advice would be very appreciated.
Thanks Chad,

[Scott Shepherd]

Yes, those that have cut thick acrylic know exactly about that flowing wave you talk about. The answer is, you can't speed it up. You need more power to speed it up and 40W is at the outside edge of being able to cut 1/2" acrylic, in my opinion, much less cut it efficiently.

[Larry Bratton]

Im new to the forum, from what I see this is a good place for advice. I consider my self to be a newbee with the laser, had it about a year and a half, have gotten pretty good but have alot to learn. GCC Laser pro spirit 40W.
Her is what i need advice with.
Had a new possible customer ask me to cut 1/2" cast acrylic, clear, he is looking to sub out the pieces as he now cuts them on a cnc but has to polish the edges clear after. He is hoping a laser will cut them clean and clear. Talking with him, if i can do it it would be 100 pieces per order, 6-10 orders per year. 2" x4 1/2" funny shaped pieces. It would be good for me.
Spent yesterday working on the settings, laser cuts through just fine, trying to get it tuned in.
So far the best settings I found is .1 speed, 30 power, 1000ppi, and i moved the table up .070" into the piece.
I have the lens that comes with it, 2"
With this I am getting a pretty good result however, and this is hard to explain so bear with me. Watching the laser cut ther is a "wave effect" as the beam cuts. the bottom of the cut lags behind the top of the cut. I assume this is due to the thickness of the acrylic. I can speed up but the lag gets worse which causes the corners to not cut well.
I would like to speed up to keep cost reasonable. Can I?? Different lens, focus closer??? Any other opinions or advice would be very appreciated.
Thanks Chad,
I'm surprised you can cut it with 30 power on a 40 watt machine ! I never use anything less that 100 power and 5000 frequency for acrylic. I have never attempted 1/2", although I have seen other posts from folks with a 40 or 45 watt machine say it can be done. 4" lens maybe?

[Michel Robillard]

Hi Chad,
Wow, 1/2" with a 40W laser, hummm, not sure
I have a 60W and for me 3/8" is about the max for a good result.
Yes I can do 1/2", but I am not satisfy 100%, but some customers are OK with that
But I must say that I am very fussy with the quality
I'm just surprise that you use only 30% of your power
I'm still a newbie, but when I cut out 1/2" I use 100% of the power of my 60W
Then, I adjust my speed very slow and I put water on the back of the material
I don't know about GCC cuz I use Trotec, setting r differents
For me, believe it or not I can do a pretty nice job with a 1.5 lens with a tickness of 1/2"
Not perfect but not bad too
I'd try with more power if I were you
And with my 60W, I know it would take about 2 minutes for a rectangle of 4-1/2" X 2"

Best of luck to you
As a newbee this is my best advice
Hope you will get better

Michel
Trotec Speedy 300 60W

[Chad Fitzgerald]

I was surprised also, i started with more power but melted the acrlic and burnt the heck out of the paper on the bottom. Still working on it, I sure appreciate the comments, more is better. Any help is appreciated.

[Rich Harman]

Iv'e cut quite a bit of 3/8" acrylic and some 1/2". The best results have been with a 2.5" lens and 4mm/s, 80% power (80 watt Reci). This gives the best edge quality for me. I can cut faster (5mm/sec, 90%) but then the bottom third of the cut then starts to get the little coin-edge ridges. If the edge quality is not an issue I can cut at 6mm/sec, and a bit faster if only the upper left part of the table is used.

I found no benefit to using a 4" lens, and the 2" lens did not cut any nicer either. If I had more power then I think a 4" lens would work better.

I also use a LOT of air assist.

[Michel Robillard]

Hi Chad,
Try to remove the paper on both sides
and put transfer tape under and I spray with a lot of water
It helps a lot for me
I'm still newbie but this is helpful for me

good luck,

Michel
Trotec Speedy 300 60W

[Mike Null]

Michel

You would get better results from a 2" lens or longer.

[Rodne Gold]

This isn't the right tool for this job , my advise is to pass on this one - I would as I KNOW it's going to become a costly PITA.

[Michel Robillard]

Hi Mike,
I have 2 lens, 1 is 1.5 and the other one is 2.5, don't have the 2"
I tried the 2.5 already but i'm not very happy with results.
May be my focus is not adjust good...
I am pretty impress with the result of the 1.5, more than 2.5
I know I should have to get better with the 2.5, may be I should verify the focus tool again.
Anyway, Thank for your advice

Best regards

Michel
Trotec Speedy 300 60W

[Mike Null]

Michel

You may have this already but if not cut what you need form 1/8" thick acrylic.

235484

[Richard Rumancik]

. . . Watching the laser cut ther is a "wave effect" as the beam cuts. the bottom of the cut lags behind the top of the cut. I assume this is due to the thickness of the acrylic. I can speed up but the lag gets worse which causes the corners to not cut well. . . .

What you are seeing is called "striations" and the laser is behaving exactly as normal. The faster you move the beam the more pronounced the striations will be. Search on "striations" and "laser cutting" if you want more info.

Are you sure you are using 30% power? I realize you are cutting very slow but I'm also surprised you can punch through at all especially at 30%. What happens to the cut quality when you bump up the power to 100%?

I don't know if you can make this viable if you have to cut at .1% speed but if you can be competitive then that is great. Unfortunately this really calls for a much higher-powered laser. (100 or 200 watts I would think.)

[Tim Bateson]

I agree with Rodne on this one. The discussion is if it's technically feasible which can become an obsession. You do need to weigh very heavily if it's financially feasible.

[Chad Fitzgerald]

Ok, just ran it again to double check my settings, .1S, 30% power(40W laser), 1000ppi, .070 focused into the piece. 1/2" cast clear acrylic. I know the 30% sounds wierd, i agree, but thats what it is.
just cut a 1/2 x 3/4" oval. edge is almost perfect except, pronounced "striation line" at the start stop spot, very small hardly noticable, and a very slight "bevel" around the bottom side of the piece.
if i turn up the power it melts, sizzles, in the cut, flames terrible underneath. if i speed it up the wave effect gets worse and make a poorer cut.
I agree with everyone at this speed it will not be financially feasable. Was hoping to speed it up since i have plenty of power left to use.
My tech rep suggested more air/exhust flow would allow more power and speed with out the flames/melting. theory being the fumes are giving the laserbeam fuel to burn. Thoughts on this?
I understand it just may not work and appreciate ALL the advice and suggestions. I sometimes have a hard time letting go when im close.
thnaks

[Rodne Gold]

We would have our air assist nozzle pointed at the cut and would have it turned up to a VERY angry hiss with air velocities at force 9 on the beaufort scale.

[Greg Facer]

We would have our air assist nozzle pointed at the cut and would have it turned up to a VERY angry hiss with air velocities at force 9 on the beaufort scale.

Really? I found, in my limited testing before I destroyed my tube, that very low air assist was working best (admittedly not 3/8 or 1/2"). Less than 5psi. I tried high PSI and the result was a terrible edge, all kinds of almost "hair" left from the combo of the cutting and the cooling.

Curious as to what PSI you were at (and was it through the nozzle?) as I should have the new tube in a few days.....it's been hanging out at the airport for a few days while DHL and canada customs get there, er, stuff together.

Thanks, Greg

[Rich Harman]

If it is through the nozzle, the lens used will make a big difference due to the distance from the nozzle to the workpiece. My nozzle is 30mm above the surface, I use 30 psi as measured about 5ft before it goes into the machine.

[Kevin L. Waldron]

If you have a way to using an inert gas like nitrogen for your air/blowing source.... you probably can get better results... but cost also climbs for the gas. This should help keep flames down to a minimum.

Kevin

[Greg Facer]

If it is through the nozzle, the lens used will make a big difference due to the distance from the nozzle to the workpiece. My nozzle is 30mm above the surface, I use 30 psi as measured about 5ft before it goes into the machine.

So, that must be with a longer lens? I think I am (was) only about 1/4" about the material with a 50mm lens. The 30psi (also about 5ft to the tip) would be pretty close to the cut.

Can't remember though if I had the 63mm lens in when I tried the higher PSI.....I might have. As you might be able to tell, I was only in the playing around stage and not taking great notes.

Greg

[Rich Harman]

Sounds like you are using a 40mm lens with the nozzle being that close to the surface.

On my machine;

65mm lens = 30mm above the material
50mm lens = 15mm
40mm lens = 5mm

[Rodne Gold]

I have no idea what the pressure is , we have centralised air thats distributed all over my factory/workshop using a massive 15hp 3 phase compressor. I NEVER use coaxial (air thu lens nozzle coaxial with beam) air assist , I have had poor results with it , I use a small directed tube of the side of the head.
For thinner acrylic stuff we balance air pressure with overcooling , ie we reduce air pressure till edges come out polished rather than "frosted" , for thick stuff we increase pressure cos we want ALL the melt expelled as melt thru the bottom of the kerf , the slow cuts and high powers involved still guarantee enough heat in the cut to polish the edges so the increased air pressure doesn't lead to overcooled and thus frosty edges.

[Richard Rumancik]

Chad, for Synrad's suggestions see this link:
http://www.synrad.com/search_apps/ap...briefs/3-1.htm (http://www.synrad.com/search_apps/application_briefs/3-1.htm)

Some of it may appear contrary to some of the suggestions above but there are often many variables that are hard to quantify (ie if you have non-coaxial air assist the performance can be quite variable.)

Synrad actually suggests that a 25 watt laser can cut 1" acrylic but you have to take this with a grain of salt. It is really not very realistic in a production environment; just because they achieved it in the lab doesn't actually mean it is practicable. And of course the quality of the edge will not appear flame-polished.

Basically you need to look at all the suggestions above and elsewhere and then it is a matter of experimentation. But whether you can make it cost effective is the question. If you think you are close, the R&D could pay off but if you need a 500% improvement in cycle time to make this job viable then I don't think it is going to happen.

A 2" lens has too short of a focal length in my opinion for .50" material (even though acrylic does exhibit the waveguide effect). I'd be inclined to try 2.5 or 3 but if you don't have other lenses to try then it ends up being a large investment. And of course the larger spot size works against you so it is speculation as to whether it would end up better overall. It's all a matter of tradeoffs . . .

Rodne, I don't know why coaxial doesn't work for you - my GCC came that way and I never had a good reason to modify it. I always thought coaxial way the way to go for a consistent airflow through the kerf. I suppose that a separate air tube would be adequate for blowing away debris, providing cooling and avoiding flare-ups but it never gave me the impression as being a very precise technique. Incidentially, the metal cutting lasers use coxial jets and they have air delivery and nozzle design down to an exact science.

[Rodne Gold]

I just found with coaxial the melt/dross/dust splatters concentrically around the cut giving me messy surfaces. (apart from dirty air messing up lenses if it also pressurises the lens box)
My earlier GCC was concentric , the explorers and spirits come with a directable nozzle. The chinese machines were concentric but the air seemed to vortex BACK into the nozzle a bit , leading to even dirtier lenses . Might be something to do with nozzle orifice size and the way the orifice edges are shaped. We took the lo tech approach and bent a plastic tube and directed it at the cut and it works :)

[Chad Fitzgerald]

Thanks again for all the advice. Ive got the cut so close to perfect im not giving up yet. speed is the issue now, Im gonna spend part of today working on that. I have ruled out a longer lens, almost 400.00 for something that may or may not work is not worth it to me. With all the advice, explanations, info., from all of you Im gonna turn the ac on, drink a few beers, and try try try. Thanks. Will let you know how it turns out.

[Mike Null]

You might inquire of these people. http://www.iiviinfrared.com/

[Chad Fitzgerald]

Thanks again for all the advice. I think Ive got it, although I ran out of scrap and am waiting for more from the customer to run more test to try to reduce time just a little.
Got it down to 4 minute run, its a shoe shaped hinge at 2.5" x 5.5". 1/2" clear cast.
My settings that are working great are .2S, 80P, 1500ppi, and i focus .125 into the material.
I also removed the paper masking from both sides. This helped alot. I have it raised off the table compared to sitting on the vector table.
My goal is to get up to .3 speed. If i can do this with the same clean edge I will get the job. 100+ pieces every month or two it sounds like.
Thanks Again for the help, feel free to add more.

[Tom Costello]

I realize this is an old thread, but I stumbled on it while searching this topic. I find that 100% power, .19 Speed, 12,500 hertz, -.12 Z offset, air assist on works well when cutting 1/2 cast acrylic on my Trotec Speedy 400 - 120 watt laser.