My lathe is old. Quite old. 76 years old. As such it also has a 76 year old 8" three jaw chuck.
The chuck is worn out. Runout is awful. At the lathe's highest spindle speed (1100 rpm), the whole lathe vibrates and therefore that spindle speed is unuseable. I know it's from the chuck because there is no vibration when I have the faceplate attached.
It's time for a new chuck, but what kind?
I still wanted a three jaw for most work. I have an 8 inch four jaw when needed. So what size of 3 jaw? Usually people always want to go bigger, but 8" (and larger) chucks have an issue, the smallest stock they can clamp on is limited. In my case it's 5/16" diameter.
I wanted smaller clamping, so I need a smaller chuck. After doing some research, a 6" seems like a good option, but what kind?
There are various types of three jaw chucks:
Two piece jaws
As for the mounting, I was kind of stuck with a plain back with a backing plate. My lathe spindle is 2 1/8" - 8 thread. It's a bit of an oddball.
In the end I decided on front mounting, plain back 6 inch with two piece jaws:
I wanted two piece jaws so I could make soft jaws if necessary and front mounting is just easier than back mounting. I went with Shars tool for both price, availability, and that the specifications are about the same.
I also needed to order a faceplate. I purchased a finished metric threaded plate knowing I'd need to completely re-machine it. No big deal though...
Decision made I purchased the parts. When they arrived, the tricky bit of machining the back plate can begin...