Reboring the tailstock

[jwmay]

I've been trying to figure out what to do about the sloppy tailstock quill on my lathe. This seems like a good solution. Anyone have any thoughts for or against?

 

[T. J.]

That's an interesting line boring setup. The methods I've seen in the past have used the carriage to push the tailstock along the ways while the tail end of the boring bar is held with a fabricated temporary tailstock. The method shown above might actually be easier to accurately set up the boring bar. You could bore the hole for the tail end bearing assembly with it mounted in place on the carriage, ensuring that its concentric to the spindle. Another advantage is that you don't have to fiddle with getting the tailstock to slide along the ways smoothly without being too loose. Of course, the size of the spindle bore dictates the diameter of the boring bar you can use, which could be a detriment on some small lathes.

 

[rabler]

I've seen variations on that. You still need to work out what to do with the quill to match, make a new one and lap it to the bore would be one solution. Moglice is another? The preferred solution from classic machine rebuilders seems to be to have the tailstock cylindrical ground, then the quill chromed and ground.

With the method shown, I'd want to bore the collar in the chuck in-place in the chuck without removing it before doing the tailstock, to eliminate any runout from the 3-jaw chuck, or dial it in using a 4-jaw. He does mention in the comments using a boring bar in the chuck to bore the carriage support.

I'm going to need to do something with the tailstock on my CK but haven't come to any conclusions on how I'll proceed.

 

[Alcap]

I wouldn’t have thought a tailstock would get worn enough to warrant such repairs ! Is the wear just at the headstock end ?

 

[Richard King 2]

In my 50+ years of machine rebuilding I have bored out 2 tail stocks. I use to send them to a shop with a Sunen hone machine (adjustable size, not on that is spring loaded) then grind the quill and chrome plate it, then re grind to the size of the honed hole minus .0005 as you need room for oil. I suspect that guy isn't a pro and it's his first one.

 

[benmychree]

I rebored an old American High Duty lathe tailstock back in the 1970s by pushing the tailstock with the carriage with a heavy weight attached to the tailstock under the bed, and held the tail bearing for the boring bar in the steady rest and chucked the boring bar in the 3 jaw chuck. Before boring, I recut the keys in the base and top casting which were loose and rescraped the base to fit the ways, after boring, I made a new keyway for the barrel that was in the form of a dovetail and made a key that was a very tight fit, then made a new barrel and fit it with a hone in the bore.

 

[jwmay]

I wouldn’t have thought a tailstock would get worn enough to warrant such repairs ! Is the wear just at the headstock end ?

There's no play left to right, but the ram can be raised or lowered .009" by hand. I don't actually know if that's enough to warrant a repair. I tried to run the anti rotation pin up against the key way at the bottom of the quill, but it'll have to be remade if I want to do that. I thought having it .009" high at all times may be better than starting out -.003 and flopping back and forth during drilling. Honestly I'm out of my depth.
Another thought I had was to counterbore the casting and install a piece to support the working end of the ram.
It's not a machine that I can freely spend money on. So if there's not a home solution, then I'll just have to get good at boring small holes I suppose.

 

[Alcap]

I think I understand what you want to do . Machine the end that’s worn , install a bushing in the tailstock , then bore to size ? Probably wouldn’t need a very long boring bar if the bushing was short .

 

[mikey]

It's not a machine that I can freely spend money on. So if there's not a home solution, then I'll just have to get good at boring small holes I suppose.

I would try to find a replacement tailstock on ebay before I would try to bore the tailstock. Drilling holes is not a big deal; you can use a chuck on your QCTP for that and bore the rest. The real problem is supporting longer stock with a live center; that has to be accurate ... really accurate. If it isn't, you'll be living in Taper City.

 

[mattthemuppet2]

First figure out if the bore or the quill is worn. If it's the quill then plating it and having it ground back to size would work. I'd it's the bore then a light skin pass, then played to that dimension (or make a new quill of you had to take allot off)