On Sep 27, 3:27*pm, Jamie M wrote:
Hi,

I bought a 4" 3jaw lathe chuck off ebay, and am adapting it as a 4th
axis for my milling machine. *The lathe chuck has a backplate with a
1.5" (1 1/2") spindle bore, and 1-1/2"-8 threads (8 threads per inch)

Is there an off the shelf pipe I could buy to thread into this and put
a couple bearings on the pipe to function as the lathe spindle? *I think
I might have to make this spindle on a lathe but it would be nice to
not have to!

cheers,
Jamie

1-1/2" x 8 is available thru McMaster Carr as threaded rod (and nuts),
but the thread class fit is 2A. You might want to spend the time
making your own piece where you can get it to fit more to your liking.