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  1. #1
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    Aug 2011
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    10

    3 jaw vs 4 jaw

    We have a Haas SL30T CNC lathe. What can you tell me about the benefits of a 3 jaw vs a 4 jaw lathe power chuck? We do far more round than square but can a 4 jaw be used accurately on round material as well as square?

    Thanks in advance.
    Andy

  2. #2
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    Mar 2017
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    273

    Re: 3 jaw vs 4 jaw

    I thought the difference is that the 3 jaw will always center your work coaxially with the center line of the spindle. A 4 jaw can be used to locate the work anywhere parallel with or coaxially with the spindle. 3 jaw cant do square stock, 4 jaw can.

  3. #3
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    Apr 2004
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    4912

    Re: 3 jaw vs 4 jaw

    Actually a 4-jaw chuck with independent jaws can be aligned more accurately to the spindle center than the 3-jaw, which will always have a little run-out (but less if the jaws were ground in place on the lathe). With the 4-jaw, and enough patience, you can get it right on. But the 3-jaw is a lot quicker to use, if absolute accuracy isn't so important. A 4-jaw scroll chuck (where the jaws all move together) is not much different from the 3-jaw, although it has more gripping power and can hold square-section stock.
    Andrew Werby
    Website

  4. #4
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    Aug 2011
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    10

    Re: 3 jaw vs 4 jaw

    This is a power chuck 4 jaw unit meaning it is on a CNC lathe and has a peddle you would push to open and close the 4 jaws. There is no way to "fine tune" the piece because all 4 jaws close and open together with each other by hydraulic pressure.

  5. #5

    Re: 3 jaw vs 4 jaw

    The main advantage I can see with the 4 jaw is that you can turn square parts. It may hold a part a bit better, but the pressure is spread out over 4 jaws rather than 3 so that may be a wash. There is some increased expense because of the extra jaw. More jaws means less pressure per jaw, so maybe less distortion of thin wall parts.

    If I were looking for a new workholding system for my lathe I would seriously look at Royal Quick-Grip CNC Collet.

    https://www.youtube.com/watch?v=VVhNPKH6hts
    Jim Dawson
    Sandy, Oregon, USA

  6. #6

    Join Date
    Aug 2019
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    295

    Re: 3 jaw vs 4 jaw

    Quote Originally Posted by awerby View Post
    Actually a 4-jaw chuck with independent jaws can be aligned more accurately to the spindle center than the 3-jaw, which will always have a little run-out (but less if the jaws were ground in place on the lathe). With the 4-jaw, and enough patience, you can get it right on.
    +1

    Couldn't turn and flip my parts around 180 deg and machine their other end without a 4 jaws. A live-center/tailstock would bend them up under that 3J chucking force far beyond drawing's tolerance.
    I agree it takes a while to get used to it, but once you know (feel?) your 4 jaws, patience isn't required anymore... takes me <1min to get a part within 1~2 micron (concentric with it floating side).

    3jaws = good for roughing operations only ;-)

  7. #7

    Re: 3 jaw vs 4 jaw

    I also agree with Jim about the quick grip collet system. Very quick, accurate, don't have to worry about concentric issues from main spindle to sub spindle on transfers. Disperses holding pressures over a much greater surface area for thin parts. Parts being machined are much more solid in the collet than jaw systems and I have been able to machine much longer parts without the need for a live center.
    Multi-Tasking Machining - Customer savings, and shorter lead times!
    www.northernmachininginc.com

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