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  1. #1
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    02-13-2013
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    Plexiglass Cutting - HELP

    I think I got lucky a month or so ago when I made a small sign for my son cut into some plexiglass.

    A friend wanted to make a back lit sign for his CO who is being transferred for an extended period of time. He asked me if we could make a sign. I said sure, and we went about designing the cut.

    At this point we have gone through $40 worth of .25" plexiglass and several end mills. When I made the sign for my son it was a very small cut and only took about five minutes. The sign we've design for my friend's boss is much longer.

    We've tried all kinds of combinations regarding speed and feed rate. Sometimes it seems like we've hit on the correct combo and one line of cut text will look very good, then as the end mill warms up the plexi starts melting and sticking to it and the cuts get ugly fast. Subsequent lines of text look horrible and we have to scrap the piece of plexi.

    On my 3040 CNC the max speed is 8000 rpms. We've tried slowing down the spindle to about 4000 rpms (just an estimate as there is no readout), and have played with a feed rate of 60 to about 95 ipm. Weve tried some cheap engraving bits, v bits, and a carbine tipped 1/16 etching bit (the etching bit drilled in and snapped the tip off in about 3 seconds).

    So...any help or suggestions we be very appreciated.

    I'll attach some examples. Some of the lines are great. The others nope. For these we were using a dremel v bit.





    Thanks,
    Dan
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  2. #2
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    Re: Plexiglass Cutting - HELP

    Yer on target with the suspect - it's heat ...

    You gotta clear those chips away - and take big enough ones so you're not doing a bunch of friction ...

    A single-flute cutter, with nice deep gullets is nice - low RPM, high feed rate -- the chances are good you just have different plastic than you did the first time which is why you got lucky last time. It's all about finding the recipe for THAT plastic formulation.

    I would suggest a good heavy air stream at the cutter, too - it will help clear the chips so you do less re-cutting and will also cool the endmill.

    That's about all I know from my limited plastic cutting experience. Leo's done a LOT more and can help - So has Viktor, no doubt.
    Jason Beam
    Sacramento, CA
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  3. #3
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    06-19-2010
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    Re: Plexiglass Cutting - HELP

    Unfortunately I don't have much to add. I have only cut plastic a few times. Depending on the plastic it will either cut or melt.

    Plexiglass is likely to be a better choice.

    I see posts where the poster will talk about cast vs (whatever else) and call one crap and the other great.

    I agree with what Jason said about process.

    Sorry
    Art and Creativity - Collide with the Functionality of CNC - priceless
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  4. #4
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    Re: Plexiglass Cutting - HELP

    Thanks guys. I'll keep trying different settings. Something has to work at some point.

    Another thought I had, it may be stupid, but what if I put a piece of plexiglass in the freezer overnight. I don't know if it will make it too brittle so it shatters or just cold enough to not melt. I would guess the condensation that would quickly accumulate would not be good for all the CNC parts, but perhaps it will keep a cold water sheen on the plastic.

    Dan
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  5. #5
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    Re: Plexiglass Cutting - HELP

    I doubt freezing will help too much since the heat you're concerned about is right up at the cutting edge and that's probably generating way more heat that it'd overcome the frozen pretty quickly.

    Start with slow RPM, high feed, blow an air stream right on the cutter the entire time it's engaged in the plastic. You can test this on your castaway material to see how it does before wrecking another fresh piece.
    Jason Beam
    Sacramento, CA
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  6. #6
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    Re: Plexiglass Cutting - HELP

    Will do. Thanks. I also ordered (or my friend did) some end mills that were advertised for cutting acrylic so we'll see how those go too.

    Dan
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  7. #7
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    Re: Plexiglass Cutting - HELP

    Here are a few excerpts from the Vectric user forum from various posters

    -----------------------------------------------------------------------------------------------------

    Not all clear plastics are created equal. Lexan (polycarbonate) cuts pretty well. Plexiglass (acrylic) comes in different varieties, some of which cut well and others don't. If you are just starting, stick with cast acrylic (not extruded) and polycarbonate. Many other kinds of plastic tend to melt, form a melted ball of plastic, then break your bit. Ack.


    If you get melting in plastic that should cut right, try slowing down your router rpm and/or increasing your feed rate. If you cut, and you make chips, that's good. If you make dust or melty bits, that's not so good. A good stream of air from a compressor can help as well.


    We have machined them into perspex / plexiglass but you do need to have
    sharp cutters otherwise you get the 'welding effect'. I believe you can get
    cast or extruded perspex and the cast version machines much better.

    Running with rapid feedrates also helps as this stops the heat building up
    on the cutting edge and stops the material welding to the cutter.

    ---------------------------------------------------------------------------------------


    Notice - "running with rapid feedrates"
    Art and Creativity - Collide with the Functionality of CNC - priceless
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  8. #8
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    Re: Plexiglass Cutting - HELP

    Thanks, Leo.

    Wonder where I could get cast acrylic or the Lexan stuff. The Plexi I've been using has just been from Lowes.

    Dan
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  9. #9
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    Re: Plexiglass Cutting - HELP

    Lowes should also have polycarbonate available. Lexan is just one brand name for it - there are likely others.

    My dust shoe uses polycarb and that cut reasonably well.
    Jason Beam
    Sacramento, CA
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  10. #10
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    Re: Plexiglass Cutting - HELP

    I haven't seen the other kinds at Lowes, but perhaps they do have it nearby. Again, I appreciate the help.

    Dan
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