Hardened Lathe Bearings Refurbishment

Morning all,

I am currently in the process of restoring the little George Adams 2 1/2" lathe that I recently purchased. Most parts seem in good condition and I am hopeful that I can turn it into a really accurate lathe for precision work.

The head stock cone bearings (look to be press fitted into the casting) and mandrel are both hardened and in overall good condition. I have blued the mandrel and I am getting good contact with the internal surface.

However, on the outer edges (that form a type of thrust bearing surface) there is some wear and galling, on both the bearing and mandrel and even a lip where it has worn in. This is causing some slight stiffness and roughness in half the headstock rotation.

Image below, but not my lathe, and actually showing the other end of the mandrel, but gives an indication of where I mean on the chuck end, which is broadly the same, but a feature of the mandrel.

Can you please help me with the following.

1/ Would it be possible to have just these surfaces reground?

2/ Would they be able to do this with the bearings in situ, or would they move them from the head stock? If they have to remove them from the headstock, will the other bearing surfaces realign again one re-fitted?

3/ Any suggestions on who to approach?

4/ Before I took the headstock off the lathe I measured the 8mm collet holder that sits in the main bore and got about 0.0001" run out. I also measured the amount of upward movement the mandrel could achieve within the bearings and this was about 0.001". This was without any adjustment - just as the lathe came. On this type of lathe, where I am looking to achieve as much accuracy as possible, how much movement should there be to allow for oil and heat expansion.

All and any other thoughts very welcome.

Many thanks,

James

I would imagine they ground them in situ originally so as to guarantee alignment so any remedial work done now would have to tackled in the same manner. the mainshaft would have been ground between centres.I also think you will be surprised how much room oil takes up!

Where I first started work there was a Lorch lathe with similar all hard spindle and bearings, now that lathe had a flat leather belt drive and oil cups for spindle lubrication,as the company were instrument makers the oil to lube the bearings was known as poilshing oil ,very similar to three in one oil,if the Shell vitrea oil (around 30 sae) was used to lubricate the spindle the belt came off as the spindle would struggle as the bearing clearance was very small.With an elderly lathe like the Adams I would be very loath to remove the bearings or put it out for grinding as there wlll not be many of todays grinding operators who understand the quality of these precision machines,I would try careful use of an oil stone to remove any imperfections and possibly some lapping with very fine abrasives,I remember our employer telling us apprentices that those Lorch bearings and mandrel were taken to a very high hardness which he described as glass hard,I consider myself very fortunate to have received a very good apprenticeship under his guidance.

I agree completely with Nigel’s analysis

This style of bearing was also used on the ‘Geneva Pattern’ of watchmaker‘s lathe, and the relationship between the steep and shallow tapers is absolutely critical.

I would only ever consider removing any ‘high spots’

Leave any pitting alone … just treat it as an additional oil reservoir !

MichaelG.

I'm with the "high spots" people, I see no need to go overboard if the main journels are good.

Thanks so much for your input everyone, looks like caution is the way forward.

I stoned down the bearings and mandrel, which has improved the feeling of 'grinding' I was getting. There is still a small difference in resistance around the rotation (i.e. one half of the turn feels lighter than the other half).

Refitting the lock screws also improved the radial play dramatically. I was getting 1 to 1 1/2 tenths just trying to lift the spindle by hand, so I am guessing with a 6" rod it would be closer to 2 or 3 (that's a guess). What would be a good radial play setting for these bearings?

Thanks,

James

The play you have just achieved would actually be less with the hydrodynamic cushioning from the oil, and I think you would try some actual turning now. The lathe is small, and you will be able to make the measurements greater by bending the spindle, which would also be the same with a factory fresh lathe. Keep monitoring the heat build up at max rpm, the headstock should not get above luke warm.

Edited By old mart on 12/06/2023 19:43:56

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Hypothetically … zero is a good number … but you do need to accommodate an oil film !

This double angle bearing arrangement is ‘quite clever’ because the thrust portion of it is designed to only-just prevent the shallow taper from locking like a Morse taper would. [hence my extreme caution about the effects of any re-grind]

Lubricants have changed a lot, and it would be very interesting to see how your lathe performs with some modern oils.

The biggest risk will come from thermal expansion of the spindle, which could lock the opposing thrusts … you must avoid that avalanche effect.

Adjust it as tight as you dare … then be prepared to back-off a little if it gets warm to quickly.

[ easy for me to say … tricky for you to judge ]

MichaelG.

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Edit: __ Old Mart is on the same wavelength 

Edited By Michael Gilligan on 12/06/2023 20:02:57

You say the image shown is not your lathe - it might help to see yours! The problems with these bearings as they wear is that most wear is on the steep taper as it is about a ten times smaller area than the shallow taper. Due to the angles involved, this can allow the wedging action that Michael mentioned, and prevent oil flow. Without seeing your actual bearings I would suggest "Timesaver" lapping compound would be worth trying ( it looks as though the image you have shown is in the process of being treated to honing of some sort)

dave8

Recommended, and reasonably relevant, reading: **LINK**

https://archive.org/details/watchmakerslathe00good/mode/2up

Note: Book page 20 appears to be missing from the PDF, but is present in the flip-book

MichaelG.

Good find, Michael, thanks for sharing! Page 20 is there in my .pdf download (but I haven't checked that all the pages are there...)

Edited By Kiwi Bloke on 13/06/2023 01:51:00

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You’re welcome

I first downloaded it in 2019 … so I was hoping that your comment meant they had corrected it

Sadly, No

… Although I should have been more explicit

The PDF does contain a notional Book page 20 [which is file page 22] … but it appears blank.

MichaelG.

As an aside:

Chapter III offers probably the definitive description of the ‘split chuck’ … and it contains [p65] the tabulation of dimensions that has been copied [without due credit ?] elsewhere.

MichaelG.

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For clarification:

Edited By Michael Gilligan on 13/06/2023 06:33:00

Possibly a glitch at your end of the download - it's all present and correct in my copy. (Bloody computers!)

.

Many thanks for that confirmation

… I will try, try, again

MichaelG.

You want to be careful not to take too much off that steep angle thrust face. If you let that spindle move very much at all axially, the long shallow tapered surfaces could come in contact and form a nice driving fit like a Morse taper.

Half to one thou is a good oil gap to start with on the main shallow taper.

Morning all,

Thanks so much for your messages - really helpful.

I will check out the book suggested - it looks very interesting.

I should have said, the readings above were with oil in the bearings.

Please see images of actual bearings below - these are after stoning.

Am I right in thinking the correct way of testing the axial load is with the tail stock? It's not a very beefy tailstock, is there a better way?

James

Edited By James Jenkins 1 on 13/06/2023 09:36:18

Edited By James Jenkins 1 on 13/06/2023 09:36:52

Your best way of testing it might be put it all together and try using it, taking a few cuts etc. Nothing like real world conditions to really see how things are.