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  1. #1
    Join Date
    Mar 2013
    Posts
    10

    Silly question

    A fee years ago I obtained 3 sets of MT3 taper metric collects sizes 2, 4, 6, 8 etc. Made in China of coarse. There are 3 slots in each collect. As I have a few spares is there any way I could enlarge the 4 mm collect to 5 mm? The 6 mm collect will not clamp down on the 5 mm tool. I thought of filling the collect with lead and trying to drill a 5 mm hole on the lathe but I am not sure if I am wasting my time. I not after super accurate just close. Any thoughts would be appreciated.
    Thanks
    Jan

  2. #2
    Join Date
    Jan 2013
    Posts
    474
    Quote Originally Posted by kenwoodhf View Post
    A fee years ago I obtained 3 sets of MT3 taper metric collects sizes 2, 4, 6, 8 etc. Made in China of coarse. There are 3 slots in each collect. As I have a few spares is there any way I could enlarge the 4 mm collect to 5 mm? The 6 mm collect will not clamp down on the 5 mm tool. I thought of filling the collect with lead and trying to drill a 5 mm hole on the lathe but I am not sure if I am wasting my time. I not after super accurate just close. Any thoughts would be appreciated.
    Thanks
    Jan
    If you can hold the collet in a chuck, adjust down until a 4mm drill shank or silver steel bar will just slide into the collet, then run a 5mm drill through the collet to ensure the hole is parallel.

  3. #3
    Join Date
    Mar 2013
    Posts
    10

    Re: Silly question

    Thanks for the idea, I didn't think of that.
    Thanks
    Jan

  4. #4
    Join Date
    Jun 2015
    Posts
    4131

    Re: Silly question

    hy i just looked for the mt3 shape, and is loooong, thus big l/d ratio

    long parts can not be easy put in a chuck, as front end, or back end, my have tir, and back end is impossible to test in a normal chuck

    but let's put asside the possible tir, as there are chuck setups designed for low tir chucking of loooong parts : even if there would be no tir, machining a collet in an opened/free state, requires real low cutting force : for example, going from 4 to 5 should not be done with a 5 drill, but 4.1 4.2, etc... and even so, the result is not a quarantee; drils may go sideways, they have their own mind, even on an 'alingned' lathe; turning instead of drililng, is more gentle, but final bore may no longer be coaxial with the collet

    to adress both tir and low cutting force, it may be better to have a custom fixture on a vmc ( helix toolpath ) or wire machine; the custom fixture should quarantee for paralelism and center, while the helix/edm is gentle enough, at least much more than a turning operation wold be

    let's supose that both fixture and machine are prepared : next issue is collet hardness

    putitng all those head to head, it may be cheaper to just buy another, or craft a new collet / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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