Mounting Hardinge Speed chuck

[yarm2111]

I have D1-5 spindle on my lathe and was going to get good used Hardinge 5C speed chuck from eBay. It was almost impossible, either price is way to high for me, or chuck looked like junk. So I ended up buying nice plain back chuck and got a D1-5 back plate separately. Machined back plate to fit the chuck and was about to make mounting holes. Plain back Hardinge chuck came with 4 holes from the front to mount it with 7/16-14 bolts. That is were I got in trouble - there is no space for the holes in the back plate - they overlap with two of the six D1-5 studs!
Per Hardinge drawing chuck mounting holes are on 4.125" (104.7mm) bolt circle. D1-5 studs are on 104.8mm bolt circle per ISO 702-2. Not sure, the cam lock mount has metric or inch origins, but both bolt circles are within 0.1mm? Possibly just rounding error.
Anyway, my plan is to use 2 out of the 6 D1-5 holes for chuck mount. The other 2 holes are going to be between the studs, no problem. D1-5 studs have M12x1 thread about 20mm deep. I'm going to make threaded insert with M12x1 outside and 3/8-24 inside, 10mm long. So these 2 holes will be shared by D1-5 studs with shortened threaded ends and chuck mounting bolts. The other 2 bolts will be standard 7/16-14, to drilled and tapped holes in the back plate.
Appreciate any suggestion and advises.
Thanks Mike

 

[mksj]

A few things to consider, it is not uncommon when mounting a small chuck like a 5C to a back plate with 6 studs to only use every other one, i.e. 3 studs. You can get a semi-machine back plate and and drill the studs/mounting holes. Alternative might be to use an extra thick back plate to give you a bit more thickness to work with. The Shar's one below does seem to manage to get 4 mounting holes with a D1-5 back plate.

7.12" D1-5 Fully Machined Lathe Chuck Back Plate for 8" Independent Chuck

www.shars.com

 

[yarm2111]

Thanks, but I have a lot of money and time invested in this back plate and would like to try to use it before buying another one.
Edit: I was able to mount this chuck as described in my first post.
Mike