Switching from 3 jaw to 4 jaw chuck

What's the make and model of your lathe?
 
It's a Hamilton 14". Not sure of the model#. The spindle is a 2 1/4" x 6TPI. There is also an adapter for the 3 jaw chuck which increases the spindle to 2 3/4" x 6TPI, so either would work for me. I have looked at Shars, and several other places, and no one has a back plate that will fit.
 
What if you bought a 2.25x8 TPI backplate and bored and threaded it for 2.75x6 TPI?
 
I've thought about doing that, but for what it would cost me for a 2.25x8 back plate that I would basically have to completely remake from scratch to get it to my specs, not to mention, I would only have one chance to get it right, I can purchase enough round stock to make 9 adapters. Being a complete novice, I kind of figure that I'm going to mess up at least the first one or two attempts. I talked with the guy who has the bar stock to see if he has any round cast bars, but he doesn't. All that he has is 12L14 or 4140HT. He says that the 12L14 is easier to machine, so I am guessing that would be the better choice for my application. I assume that this is a softer metal, and would be less like to gall the threads on my spindle.
 
12L14 has lead added to the mix, hence the "L". It is really nice to machine.

Making a plate from flat stock is fair bit of machining so lots of practice. I'd suggest practising threading both external and internal to get familiar with the dance steps.
 
I have figured out how to thread. As a matter of fact, I have made several parts for my off road Jeep. Haven't done much internal threading though. I just bought some PVC pipe to practice on.
 
mriplaybass said:
My next dilema is finding some 5 1/4" diameter steel bar. I just called the local steel yard, who sells all their steel by the foot if you don't need an entire 20' piece. $123.00 for one ft.!
Click to expand...
That happened to me with our local steel supplier. I told them that I only needed a short piece and asked if they knew of anyone locally that could accommodate me. They gave me the name of one of their customers, a welding shop, and sure enough the owner of the welding shop cut me exactly what I needed. Of course it was not free but very reasonable (if you show up when they are not too busy or can wait until they can get to it). But steel is getting expensive any way you look at it.
 
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