3 jaw vs 4 jaw

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  1. #1
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    Default 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



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    Default 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.



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    Default 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
    https://computersculpture.com/


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    Default 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.



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    Default 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.



    Jim Dawson
    Sandy, Oregon, USA


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    Default 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 ;-)



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3 jaw vs 4 jaw

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