Better to make a chuck back plate to register OD or OD of entire chuck?
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  1. #1
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    Default Better to make a chuck back plate to register OD or OD of entire chuck?

    I have a 4 jaw chuck that I need to make a back plate for. The OD of the chuck is 6", and the register face diameter is 3.5" with the bolt holes contained within. Is there any particular benefit to making the back plate a 6" OD or just having a smaller one which only goes to the 3.5" register dia? If I went with the 6" OD, it would still register on the 3.5" circle. It seems like it would just be preference at this point.

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    Quote Originally Posted by Domodude17 View Post
    Is there any particular benefit to making the back plate a 6" OD or just having a smaller one which only goes to the 3.5" register dia?
    Speaking strictly theoretically as the engineer in me wants to do...the larger backplate will provide some resistance to the cantilevered chuck deflecting under load. Conversely, if the chuck must ride farther away from the spindle nose to make room for the full diameter step, that benefit will be lost to longer stickout.

    Speaking practically, I’m not sure you could measure the difference in either case with the forces a 6” chuck will see.

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    If the precision face is the register, then make the backplate to fit that. Turning a backplate that will bear against both the face of the register and the face of the outer part of the chuck at the same time is not a trivial task. If the bolts were outside the register diameter, the choice might be different.

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    One only needs to mate the registration area.

    You could cut OD to match then face off some to make a raised area that fits the chuck.

    This would add some mass but also make chuck heavier to lift when changing.

    Just make sure chuck fully seats.

    By leaving the OD full size it can be used possibly for some other chuck someday.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk

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    Suggest you state the make of the chuck and post a pic...."some" 4j chucks are made to have full diameter backplates and the "registration" is just there to assist with centering and is not a precision surface.
    Last edited by iwananew10K; 06-14-2018 at 06:57 AM.


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