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  • source for more precise plexiglass?

    Does anyone know of a source of plexiglass that has a more consistent thickness? Bought some 1/2" from McMaster and it varies from .465 to .517 inches thick which gave me problems with the parts I'm making. Or is this inherent with the process for making plexi?

  • #2
    Looks like that is standard tolerances: http://www.eplastics.com/Plastic/Pla...eet-Plexiglass

    I've run into this engraving shallow text on acrylic sheets.

    Ken

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    • #3
      You can try contacting the manufacturer who can give you the tolerance values for each type (they vary) and where to source it. If its "True" plexiglass, (which is a trade mark name), then its made by Rohm and Haas (plant is 3 min from me and my brother worked in the lab for many years).

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      • #4
        Looks like its inherent to the process. Next time I'll use hard anodized aluminum.

        Thanks for the replies.

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        • #5
          Thirty years ago I did a lot of work with "plexiglass". After looking at several different brands, I came across Shinkolite by Mitsubishi Rayon and found that it was much more consistent in thickness than the other brands. As I recall, the other brands were wavy as I measured along the edges (can't measure very far into a sheet with a 1 inch mic), but the Shinkolite was very consistent in any variation from end to end of a sheet (a little over 4 x 8 feet). This was for the 1/8 inch material (which was in actuality closer to 3mm). I did use 1/2 inch material, but don't remember any particulars about it as the 1/8 inch material was more important to the product.

          Here is a link to the Shinkolite thickness spec page: http://www.mrc.co.jp/shinkolite/tech...fo/info03.html

          Hope this is a help.

          Glenn

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          • #6
            I have cut a lot of Acrylic with a laser. We quickly found out that there is a great variation of thickness in a sheet. The explanation we were given was that it is cast as a sheet. So it is all related to mold filling, material cooling, how level the mold is and any other variation caused by this manufacturing method. If that was "smoke blown up my Kilt" or fact I was never able to find out for sure. For sure there was a lot of variation.

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            • #7
              I think there is cast acrylic and extruded acrylic. The extruded should be more consistent in thickness.
              ----------
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              • #8
                Originally posted by SGW View Post
                I think there is cast acrylic and extruded acrylic. The extruded should be more consistent in thickness.
                Yeah. Fifth bullet paragraph: http://www.pmma.dk/Acryl_stobt_kontr...spx?Lang=en-GB

                Ken

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                • #9
                  Even with the tighter tolerance of +/- 5% on the extruded one could have up to .025" variation from the nominal on 1/2" material. Way too much for the application.

                  Now I'm looking for a supplier of anodized aluminum with a thickness tolerance of +/- .001" or less. McMaster's material has a +/- .007" tolerance which is still excessive for my purposes. If push comes to shove I can go to a local plating shop, but that will drive up the price in comparison to someone who makes the anodized material in large quantities.

                  Thanks for all the replies.

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                  • #10
                    For +/- 0.001" tolerance, you likely will to have it machined.
                    If you can tolerate +/- 0.002": http://www.mcmaster.com/#standard-al...sheets/=p3afn5 Select "Precision Ground" under Finish/Coating. Pricey!

                    Ken

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                    • #11
                      And plexiglass will slowly lose thickness over time as it slowly de-gasses. Other plastics have the same problem. They lose thickness in cross-section. ODs become smaller, and IDs become larger. And the properties change as some chemicals evaporate. General problem with plastics is that they become less "plastic" over time. And then they break.

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                      • #12
                        Originally posted by kf2qd View Post
                        And plexiglass will slowly lose thickness over time as it slowly de-gasses.
                        I did not know that, it certainly will impact my material decisions in the future.

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