Making spring collets ?
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  1. #1
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    My mind got to wandering the past couple days and I keep coming back to this.

    What is the process for making spring collets - say, like ER type? Basically I figure you would rough it out and slot it, heat treat it, then grind and maybe lap it to final dimension. But how do you hold it for getting to final dimension? Do you just wait and slot it with an abrasive cuttoff wheel after heat treating and getting it to final dimension or is there a trick you tool making gurus use? Fess up.

    Inquiring minds want to know.

  2. #2
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    Well Vinito, I just had a waterjet machine salesman stop here. He showed me a variety of parts made on the waterjet and one was a spring collet.
    Just shell out 100 grand or more for a machine and you can make all the collets you want.

    Les

  3. #3
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    Vinito,

    Making spring collets is about 50/50 machining followed by trial and error to get the spring opening correct.

    Basic way to do it is rough and heat-treat, followed by finishing ODs and ID's. Finished dimensions need to be established in the nominal clamped postion. If you cant finish the ID and OD in one chucking to guarantee concentricity, then I would finish the ID to size, then us it on a mandrel between centers, or held in a 4-jaw, to finish the OD dimensions.

    Once the sizing is done, then the collet needs to be split or segmented.

    After splitting, you need a fixture that will force open the collet to its expanded condition, while allowing it to be annealed and re-tempered in that position. When it cools, it should be sprung out oversize, allowing it to be collapsed in the chuck back to the nominal clamping diameter. The amount of forced expansion during the anneal process is the tricky part.

  4. #4
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    Lately I've only used my shop to make a few parts to repair my lawnmower. So I could 1) get that waterjet, or 2) bite the bullet and have the kid down the street mow my grass... for the next 200 years.

    Ferrous. Thanks for the reply. That sounds like a pain in the arse. I think I would skip springing/expansion the collet during the annealing and let it spring itself out in use. I was hoping there was a trick to hold the already slotted collet after heat treating to grind the ID and OD and call it done (like slipping shim stock in the slots and tightening it down somehow - but how?). I've got too many other projects so maybe I'll just continue to buy my collets. I hate to be defeated though. Maybe I'll crunch on this a bit more.

  5. #5
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    FWIW: Lindsay's Technical Books offers a reprint of a book that shows collet making, step-by-step, as practiced by a mfr. of bench lathes.

    John Ruth

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    This guy has done some SERIOUSLY impressive stuff, but here's his webpage about trying to make a collet.

    http://www.5bears.com/cnc34.htm

    Don't know what that's worth to you, but it seemed relevant.

    Justin


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