How I Made My 3 Jaw Chuck Run True
My Smithy 3 jaw chuck was running so sloppy I decided to try to make it run true.
I was hoping to get it to run with .0005" runout. One of the jaws in the chuck is off by .001". The best it will run is .001" a significant improvement from the .006" it was running.

I cut an additional .005" off the inside of the center of the D1-4 back plate to allow the chuck movement.

I drilled holes with 120 degree spacing in between the pinions.

I tapped the holes for 6mm x 1mm thread 22mm long set screws.

The front and back shcs were installed with light tension, then I centered the chuck by adjusting the set screws with a DTI to run true and tightened the front shcs's then unmounted the chuck and tightened the shcs's on the back plate. The set screws may be removed afterwards.
I did this about 3 years ago and it is still running with 0.001" TIR on a 1" gage pin.
Boomer
My Smithy 3 jaw chuck was running so sloppy I decided to try to make it run true.
I was hoping to get it to run with .0005" runout. One of the jaws in the chuck is off by .001". The best it will run is .001" a significant improvement from the .006" it was running.
I cut an additional .005" off the inside of the center of the D1-4 back plate to allow the chuck movement.
I drilled holes with 120 degree spacing in between the pinions.
I tapped the holes for 6mm x 1mm thread 22mm long set screws.
The front and back shcs were installed with light tension, then I centered the chuck by adjusting the set screws with a DTI to run true and tightened the front shcs's then unmounted the chuck and tightened the shcs's on the back plate. The set screws may be removed afterwards.
I did this about 3 years ago and it is still running with 0.001" TIR on a 1" gage pin.
Boomer
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