What do Bison quote for the accuracy of your model, both my Bison 160mm
chucks came with a booklet giving this info. Did you use the socket
marked with a 0 , that is the master socket and gives minimum runout for
a new chuck. The last one I did as you describe gave 0.0005" TIR on a 1"
test bar after mounting.

Terry wrote:

I just installed a Bison 6 1/4" chuck onto a Bison threaded backing
plate and had a few questions.

I used a step by step guide for machining the backplate on my lathe. I
machined a flat surface towards the outer edge where the chuck rests
against and the bolts go through (a spigot). I left the inner portion
.001" over so the chuck has a very tight press fit.

I measured the flatness of the backing plate where the chuck will rest
against, and it was around .0002". I did all the machining operations
to the backing plate in one session. So the plate was never removed and
re-installed again.

I then drill the mounting holes and made sure there were no burrs and
mounted the Bison chuck by using the mounting screw to suck it in
against the backing plate. I torqued all the screws in a cross pattern
(don't know if that really mattered). Then I mounted the assembly onto
my lathe.

I first checked the run-out of the chuck and it was .002". I then
mounted a 3" long standard into the chuck and checked the run-out
exactly 2" from the jaws. It was also .002". I removed and installed
the chuck assembly a few times from the spindle. I also loosened and
tightned the bolts and the runout did change slightly to .003". I had
it down to .0015" at one point, but messed with it some more and it
came back up to .003".

I am wondering why I am off by this amount. The backing plate mounting
surface was perfect. Is this normal for a Bison chuck?

Are there any tricks to getting the chuck perfectly flat against the
backing plate? I have 6 bolts so I assumed those would do the job.

Also, I was not sure if I should counterbore the back of the backing
plate for the bolt heads. Right now, the bolt heads are sticking out
past the rear of the backing plate. Is this typically done. It would
allow for more threads to enter the chuck.

Thanks for any info.