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Thread: Crack in Acrylic sheet / Tempering

  1. #1

    Crack in Acrylic sheet / Tempering

    Hello,

    I hope everbody is well! Today I cutted an acrylic sheet, and a couple hours later it cracked by itself. Does anybody have a clue why this happens? Maybe because it‘s not tempered?

    How do you temper a larger sheet?

    Thanks for help, Cheers Andrea
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  2. #2
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    was it cast or extruded .
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  3. #3
    Quote Originally Posted by Bert Kemp View Post
    was it cast or extruded .
    It is extruded
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  4. #4
    either can crack, I'm not sure which is most prone though...

    I make plex (cast) headlight covers for a guy back east who sells them, they have a long 'notch' on the sides which involve right-angle (almost ) cuts like your piece. When the first batch sold, he started getting complaints that the plex was cracking at the corners of the notch cuts. What I did to combat it was to radius the corners of the notches, and every other sharp corner.
    This graphic is of one of the notch cuts, right from my Corel job...


    The notch cut isn't very deep, the horizontal segment measures just under 3/16" long, so the radius is actually quite small..
    But- he hasn't had a complaint since, and he's asked some customers to check, no cracks
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  5. #5
    Thx a lot, Kev - that‘s exactly what I thought about this morning. I‘ll try on monday and think about a stress test
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  6. #6
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    Extruded acrylic will crack or craze after being cut, cast usually doesn't. If you aren't sure which you have then you can cut a 1" circle and wipe it with denatured alcohol - if it's extruded it will crack/craze immediately. Any solvent based cleaner will cause this as well.

  7. #7
    Maybe there is a difference in the brand, but I also made the experience that there is no difference between cast and extruded.
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  8. #8
    I agree with Gary's remarks. I avoid extruded whenever possible. I have never had an issue with cast acrylic and my "go to" cleaner for cast is denatured alcohol.
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  9. #9
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    The brand doesn't matter at all, it's all in the way it's manufactured. Cast is basically poured into a mold where extruded is a big blob that is pressed into shape. They both have very different characteristics when lasered and those characteristics determine which one is appropriate for your particular needs. If you cut extruded it will crack/craze in time, no way around it except to anneal it, and that takes hours in a temperature controlled oven with no guarantees that it will remain in the same shape/size as it started. Solvents simply speed up the crazing, but it will happen eventually anyway.

    Quote Originally Posted by Andrea Weissenseel View Post
    Maybe there is a difference in the brand, but I also made the experience that there is no difference between cast and extruded.

  10. #10
    Quote Originally Posted by Andrea Weissenseel View Post
    Maybe there is a difference in the brand, but I also made the experience that there is no difference between cast and extruded.
    So cast and extruded are made very differently no matter what brand. And to clarify. We he was talking about cutting. He meant with cutting with a laser. You can glue extruded fine with no crazing if you use a router or CNC It's mainly when you use a laser to cut extruded and then glue, or use denatured alcohol that is will craze.

    I fabricate with both materials all the time, and just different process to get a good end result.
    Last edited by Clark Pace; 03-21-2020 at 11:50 PM.
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