1921 11" Spindle Wear and New Bronze Bearings

Hi guys,
A month or so ago, I finally popped the spindle caps of my recently acquired 1921 11" SB27A, after finding my headstock was 0.050" lower than my tailstock (which should not have been the case, and after all other potential causes were dispelled). The worn bearings were nasty (see photos), and had been improperly shimmed, and at least the large bearing was subsequently starved of oil from the shim blocking oil flow, etc. I was able to get the spindle fairly well adjusted, but it needs new bearings, which is my current project. I have the 932/SAE660 bronze for the bearings, but grabbed some aluminum round for a trial and test-fit. I have OD of the large test bearing complete (on the working lathe), and am working on the ID of the large test bearing. This is where I could use some recommendations...

I was targeting ~0.001 > spindle diameter for the plain bearings, then planning to split, similar to as described here. When taking spindle dimensions, for boring the bearing ID, I've run into a snag. The spindle is tapered on both contact patches, from wear (pictured below). 0.012" taper on the large contact patch, and 0.008" taper on the small contact patch.

I could use some recommendations on how to proceed. The options apparent to me are below, with one of the first 3 being preferred:
1) Bore bearings to 0.001" > spindle smallest diameter, and hope the bearings wear in to the spindle taper.
2) Try turning the spindle contact patches back to round; easiest method coming to mind being to run the spindle with one bearing cap off at a time, while trying to stone the contact patches back to round.
3) Taper new bearings to match the current spindle wear.
And with a much larger hurdle to clear (cost and time, both of which are limited):
4) Buy a replacement spindle.
5) Make a replacement spindle.

Any recommendations would be appreciated. This is my first time making split||plain||bronze bearings, so if I've missed something big, please let me know.

Thank you,
SB27A

Original lower bearing halves:

Large lower bearing half:

Small lower bearing half:

Current spindle wear:

The idea of rotating the spindle in the lower half bearing shells might work if you had only a "thou" or two to take off but .012" is a lot of material to remove with a stone and the chances of getting it round are not good.

As a practical matter finding a different spindle might be the simplest solution.

I would offer another suggestion and I really don't know if it would work. IF you could find a really competent automotive machine shop that can do crankshaft regrinding, they MIGHT be able to index your spindle off the bore and then grind the journals straight and slightly undersize. I thought about doing that for my 9 Jr but in the end I decided to just polish up what I had and run it with new bearing shells. It's run that way for close to 20 years now and it's satisfactory for most jobs.

You can also "shoe" or "line" the original bearings (they already fit the head stock) similar to what I did to these bronze shifting forks

https://www.practicalmachinist.com/...ory/shoeing-shifting-forks-159832/#post911532

have fun

Hi Dobermann, when you say polish and run with new bearing shells, do you mean you essentially did my option 1? What kind of taper or wear were you looking at?

Hi Johnoder, I’d actually found your shoeing post, while investigating about my bearing options (prior to learning about the taper issue). Any recommendations about the taper? I already have the bearing material and other lathe booked, and was also battling the 0.050” drop issue, from the P.O. shimming them improperly. I’m not sure tapering the bearings is an option, as the bearing taper would be 0.3°, and the taper attachment isn’t that precise, so am hoping there is either some experience predicting that option 1 would work, or someone has recommendations for #2 or #3.
I suppose if I could get the chuck off the spindle, running the spindle in the other lathe would be an option, to remove the 0.012”D, however, that’s not been successful, even after heating the chuck and alternately freezing the assembly and some brute force in each case.

you should be able to leave the chuck on the spindle and center the spindle in another lathe using the chuck to hold onto a piece of stock.

or turn a center in the lathe long enough to reach through the chuck and hold the spindle in its taper. the chuck left on the spindle can be used as a dog.

for the tail stock end of the spindle a live or dead center would be adequate.

have you tried putting an ice cube inside the lathe spindle while the chuck is uniformly warm while applying torque? the hotter the chuck is to start with the better.

SB27A said:

Hi Dobermann, when you say polish and run with new bearing shells, do you mean you essentially did my option 1? What kind of taper or wear were you looking at?

Click to expand...

I was only polishing off some high spots on the spindle. It was scored and grooved so I just took off some of that with an India stone. The journals were not tapered and I doubt I could have measured what I took off.

Your existing bearings look fine to me, and are probably already tapered to match the spindle. I'd re-cut the oil channel, shim them up, file the split down a bit if they won't close, and run a heavier weight oil.