cutting acrylic

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Thread: cutting acrylic

  1. #1
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    Default cutting acrylic

    anyone else cut arcylic? i cut mostly acrylic and would like to share preferences with other fabricators. here's my data:

    bit: LMT Onsrud 63-775 Solid Carbide Upcut Spiral O Flute Cutting Tool, Inch, Uncoated (Bright) Finish, 21 Degree Helix, 1 Flute, 2.5000" Overall Length, 0.2500" Cutting Diameter, 0.2500" Shank Diameter
    acrylic thickness: 1/8" - 1/2"
    pass depth: 1/8"
    feed rate: 20ipm
    rpm: 20000
    results: not a very clean cut, slight re-weld, not as smooth as i would like.

    bit: LMT Onsrud 63-760 Solid Carbide Upcut Spiral O Flute, Inch, Uncoated (Bright) Finish, 21 Degree Helix, 1 Flute, 2.0000" Overall Length, 0.1250" Cutting Diameter, 0.1250" Shank Diameter
    acrylic thickness: 1/8" - 1/4"
    pass depth: 1/16"
    feed rate: 20ipm
    rpm: 20000
    results: pretty clean, slight re-weld occasionally.


    the re-welds aren't too bad and i can knock them off with my finger nail. i'd obviously not have any to begin with. my feed rate is way lower than what i've seen recommended online (100-200ipm). the problem is my work piece won't stay tacked down to my spoilboard if i use a higher ipm. if anyone has any advice/feedback for me, i'd appreciate it!

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  2. #2
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    Default Re: cutting acrylic

    You are basically rubbing the material off. You report a better surface finish with a smaller diameter cutter so that hints at your cutter speed being too high. Can you change the rpm of your spindle? I would try about 10k for the 1/8 bit and 5k for the 1/4". Or you can deal with your workholding issues and increase your feed rate.

    Do a bit of research into surface feet per minute (SFM ). That is how fast the cutter is moving wrt the material. Also look into chip loads.

    The recommended SFM range for acrylic is 200-600 SFM. Your 1.4" cutter is running about 1300 while your 1/8" is about 650. The speeds I suggested put you in the middle of the range.

    A general recommendation: Choke up on the cutter as much as you can. That will minimize cutter deflection and reduce chatter. Since deflection increases as the cube of the change in stick out, a little goes a long way.

    bob



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    Default Re: cutting acrylic

    Onsrud says at 20,000 rpm, your feedrate should be 200ipm for the 1/4" tool, and 100ipm for the 1/8" tool. If you need to cut slower, then you need to decrease the rpm proportionally. Cutting forces, though are not likely to change.

    So, you need to find a better way to hold your sheets or parts.

    Gerry

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    Default Re: cutting acrylic

    I cut a lot of cell cast acrylic. Usually run 100-120 IPM for both 1/4 &1/8. I favor the Amana Tools acrylic cutters, they produce good cuts with lasting results.



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    Default Re: cutting acrylic

    Thanks for the replies. I'm still transitioning from table routers to Cnc. used to 24k rpm and adjusting the feed rate by feel. I ordered some amana bits as part of my problem could be old bits.



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    Default Re: cutting acrylic

    I also need to learn spoilboard basics.



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    Default Re: cutting acrylic

    Quote Originally Posted by fortyeight View Post
    I cut a lot of cell cast acrylic. Usually run 100-120 IPM for both 1/4 &1/8. I favor the Amana Tools acrylic cutters, they produce good cuts with lasting results.
    may I ask what machine you use and how you're holding down your material?



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    Default Re: cutting acrylic

    I have a CNCRP PRO4848 and a benchtop pro. I use industrial strength two way tape to hold the material down, I also will hold the perimeter of the material with some sort of clamps, the clamps are added insurance but probably don't need them, I have never had material lift while cutting, and to remove materiel once it s cut, most times i have to use a flat top screwdriver to pry the materiel off the spoilboard, the tape holds that good.I have used this method hundreds of time with no issues


    I usually cut at about 18K rpm.



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    Default Re: cutting acrylic

    You could also try a vacuum hold-down if the area is big enough.

    Cheers
    Roger



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    Default Re: cutting acrylic

    What tape? I've tried the ds carpet tape from the home depot and it's just alright.

    Quote Originally Posted by fortyeight View Post
    I have a CNCRP PRO4848 and a benchtop pro. I use industrial strength two way tape to hold the material down, I also will hold the perimeter of the material with some sort of clamps, the clamps are added insurance but probably don't need them, I have never had material lift while cutting, and to remove materiel once it s cut, most times i have to use a flat top screwdriver to pry the materiel off the spoilboard, the tape holds that good.I have used this method hundreds of time with no issues


    I usually cut at about 18K rpm.




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    Default Re: cutting acrylic

    As others have said, you need to increase your feed rate or decrease your spindle speed. I have used the Onsrud O-flute bits with excellent results with acrylic. I don't have the exact part numbers, but I use the cutters they recommend for hard plastic. With rigidity issues or material lifting you need to decrease your RPM as opposed to increasing your feed rate.

    Take a look at the Onsrud web site. They give the recommended chip load and the formulas on how to find feed rate for a given RPM. Also, if you are not familiar with how chip loads work go to www.cnccookbook.com and read some of their articles and download the free G-wizard demo.

    You can also try the Onsrud down spiral cutters if you can't keep your material down. What I do is a test cut of the spoil board to cut about 1/8" or more into the spoilboard first then tape down the material. The cut allows you to not have tape right at the cuts since it gums up the cutter and makes chips stick. It also gives a relief in the spoil board for the downward moving chips to go into. I also use a shopvac to vacuum up the chips as they are being made.

    Now that I have a laser I hardly ever cut acrylic on the router or mill any more. Edges come out polished and no chance of cracking the material. A 40W laser will do 1/4" acrylic like butter.



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    Default Re: cutting acrylic

    Quote Originally Posted by fortyeight View Post
    I cut a lot of cell cast acrylic. Usually run 100-120 IPM for both 1/4 &1/8. I favor the Amana Tools acrylic cutters, they produce good cuts with lasting results.

    I should of mentioned that i also blow compressed air at cutter end, while cutting,
    cutting acrylic-img_0378-jpgcutting acrylic-img_0228-jpg

    Attached Thumbnails Attached Thumbnails cutting acrylic-img_0378-jpg   cutting acrylic-img_0228-jpg  


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