Mounting 4 Jaw Chuck.

[ironwrx]

Hi. I’m still learning and improving my old 16” SB lathe. I decided to try using a different chuck and learn the ways of the 4 jaw. I have a couple of four jaw chucks that came with the lathe, but the one with the chuck plate attached, has jaws that have been hammered on, (literally, and pretty beat up), also a couple of cracked jaw screws as well. The other four jaw was pretty dirty and surface rust covered, but actually in better shape. Unfortunately this one doesn’t have a chuck plate, and I’d swap the plate for the other one over, but it already has been remade and drilled out for different chucks multiple times. My question is this… there’s a fellow on marketplace who’s got a plate for $50 from a 14-1/2” SB, already has 5” diameter flange (the size of the recess in back of my chuck). Unfortunately, the bore and thread are small. Mine is 2-3/8”-6 and his is 2-1/4”-8. #1, would it work to reuse a plate that already has the od that fits the chuck mount recess, and #2, will I be able to rebore and thread for my spindle which is only 1/8” bigger? I guess # 3, is there anyone out there that has, (or know where I could get) the correct lathe plate?

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[talvare]

I don't think you'd be able to bore and thread your existing back plate successfully. According to Machinery's Handbook, the major diameter for the 2 1/4-8 thread is 2.250. The minor diameter for the 2 3/8-6 would be 2.195 to 2.226.
Shars has back plates that would probably work for you.

Lathe Chuck Adapter Back Plates - 2-3/8 - 6

Shop Shars Tool today and see why customers choose our high quality lathe chucks at a great value, same-day shipping, and dedicated customer support.

www.shars.com

Ted

 

[matthewsx]

I'd get one that's the right thread for your lathe and cut to fit the chuck, not the other way around.

John

 

[markba633csi]

Easiest route is to just buy one; might take some searching
Options are:
1) Shars, 10" dia. 2.375 x 6 = 140$
2) Shars, 6" dia. 1.5 x 8 rethread to your size = 60$
3) Make one from scratch = essentially free if you can find a chunk of cast iron (barbell?) and can cut internal threads
Personally I'd go for #3

 

[markba633csi]

If you decide to make one using your 3-jaw, make sure you can remove the chuck easily so you can carefully take it off with
backplate mounted to turn it around and test the fit. You want to leave the backplate chucked up until the internal thread is finished.
You will need to de-mount and re-mount the assembly several times as you get close to the thread finish size. Takes time and patience.