Help with Bison Chuck, can we save it?

[rakort]

Looking for help with a Bison chuck, trying to set it up for my SB 10K with a 1.5” threaded spindle.
Chuck ID:# 3205 on brass Bison tag
# 6012 stamped on face of chuck body
Chuck has 3 reversible jaws, it is a 6” chuck (160 MM ~ 6.25”)
Based on the 3205 I believe it started out life as a Bison “Universal three-jaw self-centering scroll chuck” with a plain back. I haven’t figured out what the 6012 is.
Near as I can tell, someone trashed the OEM plain back and cobbled on a threaded back plate. See pictures. The back plate looks real thin and whimpy. It is obviously not an OEM back based on the ****ty machine work.
OK So the question is how do I make this right for my spindle?
Bison back plates for plain back chucks are available, but looks like they expect the plain back to be there (and mine is gone).
The OEM plain back ties the back plate to the center of the chuck body with three screws (see pixs of plain back chuck and my chuck pix showing three threaded holes on the backside of the body near the center of the chuck). Looking at other chucks I suspect tieing the back plate to the center of the body with these bolts is a good idea from a structural integrity standpoint. If I get and modify a universal back plate it wont have these bolts to tie things together and restrain the scroll gear with the spacer show in my fingers.
Thoughts on path forward?
I think the chuck is worth saving as I believe these are good chucks, other option id fleabay it and buy a cheap import *grits teeth*

Pictures are available here:

http://www.flickr.com/photos/12814289@N08/

Thanks
Rakort

[SGW]

It looks as though somebody was after minimal overhang.

I think I would see if Bison will sell the missing part. They sell other chuck parts, so they may sell that one. That would be the simplest solution. Otherwise, I guess you could buy a 6" disk of cast iron from a place like www.mcmaster.com and make the part.

You may also want to make the threaded adapter plate to specifically fit your lathe spindle nose. I bought a Bison 3-jaw with a 1 1/2-8 threaded backplate for my lathe and found that it was a "rattling good fit." I suppose it's because a generic threaded backplate has to fit every 1 1/2-8 spindle nose ever made. I ended up boring out the threads, Loctiting in a cast iron plug, and reboring and recutting the threads. I was also able to take at least a quarter inch off the length of the spigot on the backplate so there wasn't so much overhang.

BTW, I've got a Kao Fong milling machine like yours, except it's a rebranded Jet.

[Dr Stan]

Good advice from SGW, I'd follow his recommendations.