On Dec 20, 10:06*am, "Bob La Londe" wrote:

Ok, I've been playing with my Taig mini mill ...
It uses ER-16 collets so I was thinking, "just find a chuck with a 3/8
shaft, and use my 3/8 collet" *There are a number of small inexpensive
chucks out there, but they all have a tapered shaft. *

There's a reason for that; it self-centers when mounted.
Can you get a chuck with the same taper as your ER-16
collets' exterior? Use the collet-holding taper to center the
chuck, would be my preference. Chucks with R-8 taper,
for a Bridgeport mill, are a common item.