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Thread: help Cutting 1/2" cast acrylic,

  1. #16
    Join Date
    Oct 2011
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    Quote Originally Posted by Rodne Gold View Post
    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

  2. #17
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    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.
    Shenhui 1440x850, 130 Watt Reci Z6

  3. #18
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    Mar 2008
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    Murfreesboro, TN.
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    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

  4. #19
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    Quote Originally Posted by Rich Harman View Post
    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

  5. #20
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    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
    Shenhui 1440x850, 130 Watt Reci Z6

  6. #21
    Join Date
    Oct 2004
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    Cape Town, South Africa
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    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.
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

  7. #22
    Chad, for Synrad's suggestions see this link:
    http://www.synrad.com/search_apps/ap...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.

  8. #23
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    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
    Attached Images Attached Images
    Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
    Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
    Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
    6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
    2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
    1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher

  9. #24
    Join Date
    May 2008
    Location
    Fennimore, Wi
    Posts
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    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.
    Chad Fitzgerald
    Hickory Grove Cabinetry
    Custom Woodworking/Laser Engraving
    Laser Pro Spirit 40W
    ShopSabre RC4 CNC
    55x49 cut area
    with 3 1/4 PC Router, 10" Z

  10. #25
    You might inquire of these people. http://www.iiviinfrared.com/
    Mike Null

    St. Louis Laser, Inc.

    Trotec Speedy 300, 80 watt
    Woodworking shop CLTT and Laser Sublimation
    Evolis Card Printer
    CorelDraw X5

  11. #26
    Join Date
    May 2008
    Location
    Fennimore, Wi
    Posts
    189
    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.
    Chad Fitzgerald
    Hickory Grove Cabinetry
    Custom Woodworking/Laser Engraving
    Laser Pro Spirit 40W
    ShopSabre RC4 CNC
    55x49 cut area
    with 3 1/4 PC Router, 10" Z

  12. #27
    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.

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