5C thread pitch?
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  1. #1
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    Am I reading it right that the thread pitch on a 5C collet is 1-1/4"-20? My bud bought a collet vise and the locknut they supplied won't thread onto the collets. Figured I'd chase the threads out on the nuts. Don't want to buy too many of the wrong taps in that size!
    Anyone have one to sell?
    thanks,
    -Armen

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    Yes, that's the correct thread. Beware import collets here, the threads often are not very well done...Often they're cut threads before hardening, then ground only on the OD/ID of the collet, leaving narsty threads. I know first hand as I picked up a set of cheapies for a dowel pin puller I made, and had a hell of a time fitting the clamp nut to the collet threads, though I'd checked the nut w/ a go/no-go gage. Almost every collet needed chasing to work.

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    Some of the imports use a very close metric thread.

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    The original Hardinge Cataract catalog of 1907, which is as close to the horse's mouth as you can get, says the 5C collet thread is 1.245-20.

    For those who have not heard, the C in 1C, 2C, 3C, 4C, 5C, 6C and 7C stands for Cataract, Hardinge Brothers' lathe and Mill trade name.

    That said, if you look at the Hardinge website today, it says the thread is 1.238-20.

    I have tried using a 1 1/4-20 tap to make collet nuts, and found they are very loose on most 5C collets.

    Larry

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    Sounds like it's time to make a tap on your lathe and mill. Good project and saves the price of those hefty taps bought over the counter.

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    Quote Originally Posted by lathefan View Post
    Sounds like it's time to make a tap on your lathe and mill. Good project and saves the price of those hefty taps bought over the counter.


    your kidding right?? time to learn to single-point and make new locking rings,

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  10. #7
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    Check out this video on 5C collet threads.

    Make a Hardinge Lathe Collet Drawbar 745 pt 1 tubalcain 5c - YouTube

    Here is the drawing images for reference
    Attached Thumbnails Attached Thumbnails 5c-adapter.jpg   5c-collet.jpg  

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  12. #8
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    I ran into this issue previously after I lost my patience with an "inexpensive" Chinese 5C collet indexer, and decided to make a new drawtube for it. I measured a number of 5C collets with wires, and used the highest numbers as the "fit" dimension. As it turned out, the 1.241-20 spec is what I ended up using as the nominal. I think I found that spec shown in the Hardinge drawing a little later, confirming my empirical choice.

    The Chinese indexer NOW works very well, or at least the collets fit it nicely...It's a good lesson in how to "add value"...


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