Attempt at runout reducing drill chuck arbor....

[GL]

As jwmay said, 0.0015 is excellent for a chuck. Jacob’s says max 0.003 is normal for a new one at half capacity. Similar to scroll lathe chucks, drill chuck TIR will move based on diameter clamped, which pinion hole is tightened first, if you tighten using all the holes, how much force is used, etc. Using fewer setups and turning between centers for to maximize concentricity was an interesting idea, especially with a threaded chuck (probably the least precise mounting option).

Nice work

 

[piper184]

Well the 0.0015 was the BEST I ever saw. Most of the time it is between .002 and .003 with it sometimes jumping to .006.
The lack of repeatability is the frustrating part. Every little part of the system contributes a tiny bit of the TIR. It takes a lot of fiddling to get it into the acceptable range. A BT30 taper adapter with a 3/4" threaded end would remove the collet and arbor from the equation.
So many things to make, so little time...