Square cross-section tailstock quill (lathe)

[extropic]

I am posting this in the Machine Restoration forum because I think followers may have the experience to provide the best answers.

I've been thinking about building an alternative tailstock for my 12x36 (Taiwan) lathe.
Why, you may ask? We'll just call it a mental exercise for now. I may never get around to building it.

My existing tailstock quill has the typical (to low quality lathes) slot in the bottom. The tailstock housing mounts a setscrew which engages the slot and prevents (very poorly) the quill from rotating. That design is so poor that it makes me a bit angry just to think about it.
One way to improve the design would be to cut a matching keyway in the quill bore and securely mount a long, square key. Maybe I will.

My question here is, has anyone ever seen a lathe with a square cross-section tailstock quill? I never have.
However, I'm attracted to the idea and can't think of any reason why it's ill advised. Anti-rotation bearing area would be greatly improved.
What say you?

 

[JimDawson]

It should work. I think the reason that all tailstocks are round is that it is much easier to bore a round hole than a square one. But a square hole with adjustable gibs should work well.

The long key might be easier to implement.

 

[darkzero]

I've never seen one either but like Jim my guess is that the TS ram is round cause it's easier to make the TS. A square ram TS would need to be made 2 pieces or perhaps with a shaper? Do they make square broaches that big? And how would it be honed or whatever?

My import lathe doesn't use a set screw for anti rotation. It has somewhat of a key but yes mine was sloppy too. I made a new tighter fitting one when I installed a DRO scale on the TS. My stock one had a groove on it which I assume was put there to help it shear if a mishap were to happen. I did not cut a groove on the one I made, I just made it out of mild steel. Not sure if I should have used a better grade of steel. Probably fine for what I do.

 

[extropic]

Thanks fellas. I agree with you on the ease of making the cylindrical quill in production.

As far as making a square quill, I was thinking surface grind the outside and scrape/flake if necessary. Turn the internal features in a 4 jaw w/steady rest (put a diameter on the outside of the taper end for the steady rest). For the TS body, mill and scrape an open top channel. Bolt on top cover with dual clamp screws. I wasn't thinking any gibs at all. On a privately owned hobby lathe, I was thinking it would never see enough wear to get as sloppy as the OEM new out of the crate. Incorporating a gib would certainly complicate things.

Like I said, it may only be a mental exercise. I appreciate your feedback anyway.

 

[darkzero]

Like I said, it may only be a mental exercise.

I hope it may be a physical exercise.

I sure would like to see it. Hmm, thinking about it, maybe not actually square would be needed. Say round with one or two flats? One flat would be much easier to make. Make the round ram, then put a flat on it. Then the top cover could be used for the flat. Heck you could even do that to your existing TS, just lob off the top & make a top cover. That is if there is room for screws & you are brave enough. I know I wouldn't be.

 

[benmychree]

Ever heard the phrase about "reinventing the wheel"? A tailstock should definitely have a key to prevent quill rotation, but it need not be very long, perhaps less than one inch on small lathes.

 

[petertha]

My '97 Taiwan 14x40 lathe has a similar looking POS key that looks like it was freehanded with a grinder (and then nicely hardened go figure). But the slot was in great shape so the issue is the gap fit and the short length. Both easily remedied with a new key. I lapped mine up a bit just to make it slide better but have plans to make an improved one.

Before you go hog wild on a new tailstock, there are quite a few other little sub-projects to deal with - bearings, lubrication, leadscrew insert nut, perfect fitting MT socket (likely hardened).... etc. I'm sure its feasible but only you can decide if its worth the effort. What I would prefer is one of those 'action handles' where you can move the entire quill range. Very useful for pecking or feeling the drill progress. Can still be locked for TS support. Stefan.G did a video showing his mod. I've contemplated buying a new/used TS just to have a complete spare in case things didn't go according to plan.

 

[extropic]

@petertha,

You've given me more food for thought.

I watched Stefan Gotteswinter's video that included descriptions of his tailstock mods.
Very good ideas.