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Modify 3 jaw chuck.

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  • #46
    Originally posted by old mart View Post
    . Just think of how the workpiece is held onto a mill bed, nothing but friction, no register and mostly interrupted cuts. There is never a worry about that is there?
    Hats off to you Old Mart if you've never had work shift in the vise, chuck, while clamped to a faceplate or clamped to a mill table. I guess if you are using an old, worn out chuck you might need .020 inch of play in the register. My worst cheap china import chuck only has around .003 TIR, but that's in the scroll so nothing to be done about it other than use it as it was designed to be used.

    I don't know if I'm abnormal or not, but once I set up a backplate for a chuck it is dedicated to that chuck. Since I do it that way, the faceplate is tailored to the spindle and the chuck and everything is a nice, tight fit. I don't usually need to take a chuck off a backplate to mount it on another backplate so that I can use it on another machine. I don't have to worry about readjusting the chuck's alignment every time I switch from the 3 jaw to the 4 jaw and back. Even my set true clone has a close fit register and (thanks to being under abused) a scroll that is very consistent so when I mount it a quick check to confirm that I did not screw something up is all it takes.

    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.


    • #47
      We sometimes do some pretty nasty things like cutting the corners off a big square plate or similar that will kick at the register more like an impact wrench. The closest comparison I would say we see on the mill would be a flycutter taking too large of a cut and hammering at the item in the vise. I tend to agree that it's very likely that the chuck would not wander around on the backing plate. But I would prefer to have a good fit myself.

      And while not perfect .005 on an old chuck with a hidden past is not all that bad. It's not great by any means but it's not bad.

      And we still come back to the idea that if tighter tolerance is needed for parts that get flipped around then a pretty basic and valuable skill is knowing how to change to a four jaw and center the item correctly. There's times where the four jaw is the ONLY way. So if the group at the workspace is going to need to learn how to swap chucks and use the four jaw ayway why not just go with that?

      In the end though if it is the scroll in the chuck that is out then there's nothing to be done for it unless it's out very consistently with respect to the body. But any runout in the scroll would by it's very nature wander around and not be consistent so cutting down the register would not help for other than a very few particular sizes anyway.
      Chilliwack BC, Canada