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Thread: Polycarbonate Shrinkage?

  1. #1

    Default Polycarbonate Shrinkage?

    I have a question for the old timers. I drilled a 1/2" hole through 3/4" polycarbonate sheet. The resultant ID was .507 - larger than expected from a .500" drill bit - maybe some wabble - but a useable dimension. Then I drilled the same 3/4" sheet lengthways (about 3") with the same bit and the hole ID is .496. So what happened? Did the lengthways bore cause the plastic to shrink? Very puzzling....

  2. #2
    Join Date
    Aug 2002
    Location
    Menlo Park, CA
    Posts
    967

    Default

    While drilling a deep hole, the plastic and drill will have warmed more... and could then deflect away from the bit?

    info on polycarbonate...

    - Bart
    Bart Smaalders
    http://smaalders.net/barts

  3. #3

    Default My thoughts

    After contemplating this for a day or so I have come to the following conclusions none of which are really good but I can live with them. In the first hole through the 3/4" dimension the .507 from a .500 bit can be chalked up to 'bit wabble'. The second hole of .496 from a .500 bit appears to be the result of the material heating up (slower feed rate than the first) then expanding into the ID even though there is no detectable bulge or expansion on the outside of the material. Another thought is polycarbonate sheet must have a pronounced grain to it - expanding and contracting differently in different directions when slightly heated then cooled. It's an interesting material to work with - lots of personality to be dealt with.

  4. #4
    Join Date
    Nov 2009
    Location
    Ontario
    Posts
    970

    Default

    Did you drill a .500 hole without a pilot?
    I'd probably use 3 or 4 sizes to get to .500 and that's just for the 3/4" depth.
    I'm not sure what I'd do with the 3" deep hole.
    Mike

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

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