I'm making steady progress on my Clausing 4914 rehab and in anticipation of finally being able to make some chips I'm starting to plan out my first few projects.
Absolutely no tooling came with this lathe, so I have to start from zero. I bought a backplate adapter from AMTOOLS that fits the rare 1-3/4 x 8 spindle nose of this lathe. I plan on using this backplate on a new Shars 6" 4 jaw independent chuck.
The problem is that the diameter of the spindle register is slightly undersized so that the backplate can not be screwed completely on to the point that it abuts the spindle face. I judge the discrepancy as less than a 64th of an inch (sorry I'm an architect I'm still getting used to using decimal dimensions). As I understand backplates and chucks, the accuracy of the surface of the spindle abutment face is what really dictates the alignment of the backplate, NOT the accuracy of the threads.
My plan is to mount the backplate on the spindle backwards, and bore out the spindle register diameter so that the it can fully thread onto the spindle. However I will be relying solely on the threads at this point to machine that diameter. My question is how accurate does the clearance need to be for that spindle register diameter? Can it be slightly over sized since the real workhorse in accuracy is the spindle abutment face?
Which brings me to my next question. Can I rely on the machined surface of the spindle abutment face from that factory? Or while I have the backplate mounted backwards should I also machine that face so that it aligns with my lathe? Again, same question as before, if it's only being held on by the threads how accurate can I expect that face to be machined? Am I worrying too much at this point?
Finally, I have one more concern. Since I have absolutely no way of holding anything in the lathe until I get this backplate fitted to a chuck I have no way of practicing any machining. So this boring and facing of the backplate could possibly be my first operation ever on a lathe. Obviously I don't want to screw up my brand new backplate. What are my options for mounting something in the lathe to practice on without a chuck? I was thinking of mounting some practice stock between centers, however I don't have a faceplate to drive a lathe dog, as well as wouldn't that also require me to center drill the practice stock? How do you center drill the stock without first being able to put it in a chuck? I could just center drill in a drill press but I don't know how accurately on center I can get that way. Although I'd assume for practice it won't matter all that much.
I guess I have a sort of chicken and egg problem. Or maybe more that I can't get there from here.
Here is a sketch just to illustrate the terms I am using in this post.