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  1. #1
    Squelch the weasel.
    Reputation: JaquesN's Avatar
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    has anyone tried surface grinding 8020?

    I'm using some aluminum extrusion scrap for a small fixture that holds the BB shell and the rear dummy axle. The problem is that my bb post doesn't sit flat on the 8020. The extrusion is convex. This got me wondering if I can use it at all for a larger fixture.

    Has anyone tried surface grinding it?

    Has anyone found a flatter alternative? I was thinking square steel tubing might be straighter.

    Thanks for your input.

    Jim


    rudimentary jigginess by jimn, on Flickr
    Last edited by JaquesN; 08-13-2013 at 03:09 PM. Reason: I meant to say "square tubing" not round.

  2. #2
    mtbr member
    Reputation: adarn's Avatar
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    Interesting, That doesn't look like the 8020 that I have.

    When I was building my jig with 8020 I considered facing the extrusion on a mill, but checked it on a surface plate first and found everything to be +/- .001" Which is just as good as I could get with the mill.

    Cool fixture btw!

  3. #3
    Nemophilist
    Reputation: TrailMaker's Avatar
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    Hey;

    I would say that a quick pass with a fly cutter on a mill would clean it up nicely enough.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  4. #4
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    Reputation: dr.welby's Avatar
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    Quote Originally Posted by adarn View Post
    When I was building my jig with 8020 I considered facing the extrusion on a mill, but checked it on a surface plate first and found everything to be +/- .001" Which is just as good as I could get with the mill.
    It's pretty good overall, but they cup the face slightly by angling the flanges in towards the cavity by a couple degrees. This is supposed to add some preload to anything bolted to it, kind of like a lock washer.

    The easy fix is to rely on the outside edges by spanning the slot with something the width of the extrusion. They have a bunch of plates that would work, for adding air lines or mounting casters.

  5. #5
    Squelch the weasel.
    Reputation: JaquesN's Avatar
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    Quote Originally Posted by dr.welby View Post
    The easy fix is to rely on the outside edges by spanning the slot with something the width of the extrusion. They have a bunch of plates that would work, for adding air lines or mounting casters.
    OK. This is very good information. That explains why everyone uses the manifold plate.

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