Help with fixturing (??) to modify a small, hard to hold, part
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  1. #1
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    Default Help with fixturing (??) to modify a small, hard to hold, part

    Hi all!
    I have 55 pcs of this part to modify.
    20190716_093921.jpg
    20190716_093749.jpg


    We could use lathes, or milling machines.

    We need to remove about 0.025" from the length, in 2 places.
    The end of the Ø.244" boss, and the face of the 0.370" square portion. (pen tip is pointing towards the surfaces)

    The length tolerance is 0.002" and we need to hold concentricity as well, to not remove any of the Ø.244 diameter.

    My thought was to hold the part on the square, in custom made vise jaws.
    Each jaw would have a 90° vee, cut 45° off axis, (think tap wrench jaws) above an undercut radius, to allow for clearance on the gear teeth.
    The shaft would sit on the large surface area, at the bottom of the gear teeth.
    The matched vee in the front and back jaws, allow for indicating each part (if required) and should allow for repeatability.

    I was thinking of making the jaws from something harder than the shaft material, so they wouldn't wear/move/change over the small quantity of parts.

    ~~~~~~~~~~~~~~~~

    What is a better / faster / more dependable option?

    Thanks all,

    Doug.

    ETA. sorry for the ridiculously small screenshot. It will not upload in large size.
    Attached Thumbnails Attached Thumbnails screenshot-2019-07-16-09.35.36.jpg  
    Last edited by doug925; 07-16-2019 at 10:06 AM. Reason: stupid small thumbnail

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  3. #2
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    Whatever you do, I suspect you'll have to dial in the .244 diameter each time to make sure you don't cut into it.

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    If you have a wire EDM available you could cut the gear profile into a collet for either a lathe or a mill. If in a mill, probe the end for length. If on a lathe set the depth with a dowel pin in a toolholder, pushing the part home.

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    Collet on the gear o.d. in a vertical collet holder on a mill, even if you use an e-collet. Less work to make and should hold fine for the amount you are removing. Probe?

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    I'd probably try it in the lathe first, collet or soft jaws on the gear and tailstock in the center. Throw an indicator on it and see what it looks like.

    If it looks good, face off the square with a grooving tool, retract the tailstock and (gently) face the end.

    That is if it's not carburized, in which case it might be a OD grind job, or setup the tool post grinder on the engine lathe...

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    I wonder if you could load the part through the back of a .375” square collet? (So the .244” boss and the tippy tip of the .370” square are sticking out past the collet nose.) For 55 pcs I bet you could get a soft collet and bore any clearance you may need for the gear teeth behind the lands of a standard .375” square collet. It would be nice and rigid, too!

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