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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Avid CNC > Trying to cut 1/2 acrylite cast acrylic. Have tried everythin
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  1. #1
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    Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    I am trying to cut two parts from some cast acrylic sheet and am having zero luck. The acrylic keeps melting the plastic and welding to the bit no matter what feed/speeds I try.

    I am attaching a copy of what I'm trying to make. Any help would be greatly appreciated.

    Attachment 318850
    Attachment 318852

    I'm trying to use an Onsrud 63-520

    I have already wasted a big chunk of the acrylic I bought. If someone can help that would be great.

    Machine is a pro4896 nema34

  2. #2
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    Apr 2004
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    5728

    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    It sounds like your RPMs are too high. If your spindle's going too fast for the bit you're using, the plastic will melt rather than cut. A vortex chiller can help too; it uses compressed air and cools it with a venturi, so it helps the plastic to stay cool, and blows the chips out of the cut.
    Andrew Werby
    Website

  3. #3
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    Jun 2013
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by ericclinedinst View Post
    I am trying to cut two parts from some cast acrylic sheet and am having zero luck. The acrylic keeps melting the plastic and welding to the bit no matter what feed/speeds I try.
    awerby has good advice. Keeping the tool and material cool is the key - though some tools have a higher/more forgiving range of acceptable feeds & speeds.

    We've used the Freud Up-Cut Spiral 1/4" tool with great results on acrylic (1/4" (Dia.) Up Spiral Bit - Straight Router Bits - Amazon.com).

    In general you've already hit on the fact that heat is the greatest variable to manage/reduce to get good results with cast acrylic.

    The heat challenge gets more difficult to manage with smaller tools, so I'd stay at or above 1/4" if you can.

    Here is a clip from one of our cutting videos on a PRO machine with the Freud 1/4" spiral tool and a Bosch 1617 EVS router (watch from 1minute 35seconds)
    https://youtu.be/htidJa2IhKY?t=1m35s

    Good luck, let us know how you get on!


    -Nathan

  4. #4
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    Perfect nate. I can get one of those bits. What's the feed/ speed and depth of cut?

  5. #5
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by ericclinedinst View Post
    Perfect nate. I can get one of those bits. What's the feed/ speed and depth of cut?
    In the video clip I referenced - that was 120 IPM @ .125" DUC.


    -Nathan

  6. #6
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    Quote Originally Posted by CRP View Post
    In the video clip I referenced - that was 120 IPM @ .125" DUC.


    -Nathan
    How about router speed?

  7. #7
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    381

    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    I cut acrylic regularly with 6mm single flute 1500-2500 rpm 1-2mm doc 1500mmpm and get results good enough to weld with Dichloromenthane, slow and steady

  8. #8
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    Quote Originally Posted by Louis_Cannell View Post
    I cut acrylic regularly with 6mm single flute 1500-2500 rpm 1-2mm doc 1500mmpm and get results good enough to weld with Dichloromenthane, slow and steady
    My spindle only goes as slow as 8krpm

  9. #9
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    Jun 2014
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    The onsrud 63-520 should cut it very well. I've used that bit in cast acrylic at 8000rpm @ 2.5m/min and it felt as though it would have been okay to use some more rpms. Could the bit have been blunt? Or you were simply going to slow @ to many rpms.

    What spindle are you using? Is that 8k accurate do you think?

  10. #10
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    381

    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    With min 8k rpm need to increase feed to counter definitely single flute I use cheapies with acrylic min 6 mm.

  11. #11
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by Louis_Cannell View Post
    I cut acrylic regularly with 6mm single flute 1500-2500 rpm 1-2mm doc 1500mmpm and get results good enough to weld with Dichloromenthane, slow and steady
    Louis, what spindle are you using?

    Sent from my SGH-I337M using Tapatalk

  12. #12
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    1/4" O-flute bit....16-18K rpm and around 100 in/min cuts fine.
    you can slow the rpms down to 15k and the feed rate down to 70 inch per min
    I just cut some 1/4 inch today with no problems.
    If you are doing a perimeter cut, cut halfway down first..

  13. #13
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by alevitt53 View Post
    1/4" O-flute bit....16-18K rpm and around 100 in/min cuts fine.
    you can slow the rpms down to 15k and the feed rate down to 70 inch per min
    I just cut some 1/4 inch today with no problems.
    If you are doing a perimeter cut, cut halfway down first..
    Yes, that looks right to me, give or take. Plexi is maybe funky / not cast? Cast should be quite easy unless you are moving really slow! A dull or damaged bit also could cause the melting described, and starting at an extremely slow rate would heat up the bit and dull it more quickly so bit that started OK could be hooped now.

    Did the OP post his own speed and feedrate?

    Sent from my ASUS_Z00TD using Tapatalk

  14. #14
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    Quote Originally Posted by gfacer View Post
    Yes, that looks right to me, give or take. Plexi is maybe funky / not cast? Cast should be quite easy unless you are moving really slow! A dull or damaged bit also could cause the melting described, and starting at an extremely slow rate would heat up the bit and dull it more quickly so bit that started OK could be hooped now.

    Did the OP post his own speed and feedrate?

    Sent from my ASUS_Z00TD using Tapatalk
    that is fast spindle wise. 100ipm can happily be cut between 8-10k with o flute. 15k on plastics that slow Sounds crazy to me.

    Your chips should stay chips, if your chips are fusing together on exit, too many rpms.

  15. #15
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    It's not, although I use onrud 63-712 and a little faster feed (125ipm) normally. Probably you are right overall, but faster rpm (which might wear the bit faster) is better than a snapped $20-30 bit.

    Sent from my ASUS_Z00TD using Tapatalk

  16. #16
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    Quote Originally Posted by gfacer View Post
    It's not, although I use onrud 63-712 and a little faster feed (125ipm) normally. Probably you are right overall, but faster rpm (which might wear the bit faster) is better than a snapped $20-30 bit.

    Sent from my ASUS_Z00TD using Tapatalk
    2mm doc @ 8-10k 100ipm 5mm bit. Absolutely fine. At 100ipm the only thing I can think of that I'd use over 13k is when engraving. And at 13k and over I make sure I'm using balanced bits. Knacker your spindle bearings quick if using higher speeds a lot with unbalanced bits.

  17. #17
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by Jon.N.CNC View Post
    2mm doc @ 8-10k 100ipm 5mm bit. Absolutely fine. At 100ipm the only thing I can think of that I'd use over 13k is when engraving. And at 13k and over I make sure I'm using balanced bits. Knacker your spindle bearings quick if using higher speeds a lot with unbalanced bits.
    To each their own. 5mm bits versus 3mm bit would also make a huge difference (even 4mm is much less likely to snap off than 3mm). I run 6mm version (63-725) at 18k rpm, 175-200 ipm in acrylic, max d.o.c. of .25"

    I've run acrylic for 20 years, those numbers work well enough for me and my customers with my particular machine.

    Sent from my ASUS_Z00TD using Tapatalk

  18. #18
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Quote Originally Posted by gfacer View Post
    To each their own. 5mm bits versus 3mm bit would also make a huge difference (even 4mm is much less likely to snap off than 3mm). I run 6mm version (63-725) at 18k rpm, 175-200 ipm in acrylic, max d.o.c. of .25"

    I've run acrylic for 20 years, those numbers work well enough for me and my customers with my particular machine.

    Sent from my ASUS_Z00TD using Tapatalk
    And I usually did 22k rpm and 70 to 100ipm on my last machine, usually 20k and 150ipm on my new one. I'll only ever have melt if it's a smaller diameter bit or a dull bit. But we're cutting plastics all the time basically, no wood or aluminum without knowing it will greatly reduce bit life (ie we'll likely never use that bit on acrylic again).

    Sent from my LG-D852 using Tapatalk
    In case anyone is wondering, I'm the twin of the other gfacer on cnczone...

  19. #19
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    BTW I've used that acrylic bit from onsrud and it works great typically. Somewhat better than the regular 63-725 which is of standard bit for thick cast material.

    Still use the same feeds and speeds for both. I don't think I've ever slowed down a speed on the spindle, I've only ever adjusted the feed (lower usually).

    Sent from my LG-D852 using Tapatalk
    In case anyone is wondering, I'm the twin of the other gfacer on cnczone...

  20. #20
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    Re: Trying to cut 1/2 acrylite cast acrylic. Have tried everythin

    Of course the other thing to try is an offset of .01" on the cutting and a full depth finish pass on the actual profile. That cleans out the melt sometimes and cleans up the edge. Usually I don't need anything like that with spiral up cuts, but pretty common for straight flute cuts in plastic.

    Sent from my LG-D852 using Tapatalk
    In case anyone is wondering, I'm the twin of the other gfacer on cnczone...

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