# 3 Jaw Chucks And Concentricity



## cdhknives (Jun 23, 2016)

I know 3 jaws are limited in repeat-ability, but:

If I am making a muzzle brake or suppressor mount and require a high order of concentricity between internal threads and a smaller boring though solid rod stock...

Am I pretty much assured of good enough concentricity by not removing the stock until all boring and threading operations are done, even in a 3 jaw?


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## Dan_S (Jun 23, 2016)

Yea, if all the turning has been done without  removing the part from the chuck, then your part will be as a accurate as the machine is capable or producing.


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## intjonmiller (Jun 23, 2016)

If the piece never moves from the chuck between operations you are assured of complete concentricity, as long as the chuck is mounted solidly to the spindle. If you have to be precisely concentric with an existing surface, inner or outer, that's another matter. But if you're machining all surfaces then you shouldn't have a problem. 

If you need to remove it for checking fitment and then replacing it you can improve your odds greatly by making a mark on the part and a mark on the corresponding jaw, then ensuring that it is re-chucked in the same position.


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## Wreck™Wreck (Jun 23, 2016)

For a high level of contcentricity  always use an adjustable 3-jaw chuck, high end 3 jaw chucks will still give you .001-.005 differences as they are medium level production tools.
Make 100 parts per day that are +-.005.  this works well, if you are a hobbyist that requires tenth's accuracy this is not the way to flip parts and be happy.


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## planeflyer21 (Jul 12, 2016)

When taking courses at the local college, we were doing a project one day and ran out of time.  One of the instructors said I may be able to reinsert the piece into the 3-jaw exactly as it was before, if I carefully marked the workpiece and jaws.

He was right.  Surprised me greatly and my fellow students.


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## 4GSR (Jul 12, 2016)

planeflyer21 said:


> When taking courses at the local college, we were doing a project one day and ran out of time.  One of the instructors said I may be able to reinsert the piece into the 3-jaw exactly as it was before, if I carefully marked the workpiece and jaws.
> 
> He was right.  Surprised me greatly and my fellow students.



You can do this on a chuck that is in good shape and hasn't been abused and molested.  I have two older Buck Adjusta True chucks, 8" and 9", saved from the scrap bins, that were used as mill fixtures.  Both were filled with crud and one had rust from coolant.  Took them apart, cleaned, lightly greased, put back in service.  They both will repeat within .0005"-.001" depending the size you chuck on.


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