need to make a new spindle for my ancient mini lathe

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mattthemuppet2

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hmm, not sure this is the right sub-forum, but here goes :) I've been having problems with runout/ wobble on my ancient mini-lathe (http://www.hobby-machinist.com/showthread.php?t=19650) where a piece of rod would swing in a circle instead of rotate around its axis. I thought I'd diagnosed and fixed the problem with help from the homeshopmachinist guys as a damaged chuck register from someone using vice grips on the spindle. Unfortunately, after some heavy use the spindle is either bent or the headstock (the bearing surface) is worn, with daylight visible between the back of the register and the headstock on the toolpost side, but not the motor side. It also drinks oil - pretty much as soon as I put oil on the wicks at the top, it runs out the bottom, even though the spindle preload is just right.

So, I've been doing some thinking, head scratching and reading, and in my mind the best fix would be to make a new spindle, this time with proper bearings (angular contact or taper roller at the chuck end, not sure about the other end). However, this would entail boring out the head stock to fit the new bearings. I'm not especially precious about this lathe, it's a tool and as it stands, not an especially accurate one. I also have the help of the machinist at work who'd be happy to give me a hand and has some big machinery and decent measuring tools to hand.

However, before I even get that far, I'm hitting issues finding appropriate bearings. The problem is the width of the headstock. Here are the dimensions:

headstock
width (widest point) 1.4in/35mm
width (chuck register) 1.1in/ 28mm
depth 1.3in/ 33mm

spindle
length from face of chuck register to end of preload nut 5.8in/ 150mm
diameter at chuck register 1.1in/ 28mm
diameter at pulley mounting point 0.7in/ 17.5mm
spindle thread is 3/4in 16tpi

The largest ID bearing I can fit would be a 7002 with a 15mm ID/ 32mm OD, but that leaves just 1.5mm either side in the headstock give or take. 7001 would be 12mm/ 28mm which I'd be happier with, but then the spindle diameter would be even smaller which is the opposite direction I want to go in. I'm starting to think that I may be better off thinking about making a new headstock from scratch, even though this would be more money and work, just so I can fit a more suitable bearing, like a double row angular contact or even a taper roller bearing if I can find one small enough.

What do you all think? Any other ideas that I've probably missed?

If/ when I do end up making a new spindle, I was thinking about using 4140PH/HT for the spindle and tapering the nose to take an ER16 collet (making a matching 3/4in 16tpi chuck nut) while I'm at it. Thoughts?
 
Matt, as nice as roller bearings are, I'm thinking you might be better off turning some new ones from oilite bronze. As you indicate, there isn't much available room on that headstock casting. (Thanks for the link to the pictures - I was having a hard time visualizing a headstock that narrow.)

My big Swedish lathe has bronze bearings, and it's still pretty solid for 70 years old. They may have forgotten to squirt in some oil from time to time. Easy to do.
 
thanks Hawkeye, you know I hadn't even thought about using olite bushings, that's a great idea. Wouldn't that require a hardened and ground spindle though? I can reuse the rear spindle insert thing (keyed to the spindle), but I'd have to do the chuck end taper from scratch. It'd certainly give me a lot more flexibility with the design.
 
Matt I doubt the spindle on that wood lathe would satisfactorialy replace your original.
Most likely as your original appears to have cast iron bearings your spindle is already hardened and ground from new. Pretty rare to find a "soft" spindle.

Cheers Phil
 
thanks Phil. I was more wondering if I could modify the whole headstock as a replacement, rather than just the spindle. I don't think replacing just the spindle on my lathe is going to work, mostly due to the hardening and grinding of a replacement is beyond my means, so I'm leaning towards replacing the whole headstock+spindle. I saw a lovely Taig headstock on eBay, which would be perfect, but the $150 asking price is way beyond what I can afford right now. I would try and work around the problem, but I'm starting to work on jobs longer than a couple of inches more frequently and the runout is getting pretty frustrating.
 
Matt
Your probably doing so but I wanted to remind you to find the true source of the problem before spending money on fixes.
It's really hard to warp a spindle but it could be put on V-blocs and checked for run-out. You'll have to remove it to replace bearings anyway.
I didn't notice how far out the chuck wobbled on you.
I like the idea of oillite bearings. A bit of old school that has served well for generations.
 
thanks Jim, good advice. A while back I spent a bunch of time hunting down some runout and traced it to a mangled register using a DTI. After I faced the register and knocked down a couple of burrs on the back of the register (from someone using a vice grip on the spindle) it ran relatively straight, even without using a dead center. There also wasn't the gap behind the register on the toolpost side.

I'll borrow the DTI again and check the inside of the spindle bore and the face of the register. To be honest, I'm probably dreaming if I think I'll have the time over the next 3 months before we move to do anything about this anyway. Most likely I'll just work around it and hope that I'll end up somewhere surrounded by cheap quality iron :)
 
Matt are those headstock bearings split? Maybe just a matter of removing some shims to tighten it up again.

Cheers Phil
 
Have you considered straightening the original spindle? I'm sure you could get it close and then skim the face of the register true.
 
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