Another bush drilling question

Since the oilite bush thread is drifting off topic can I ask a related question? My Myford S7B runs beautifully smoothly but the right hand countershaft bearing eats oil and has for a long time. I recently dismantled it to take a look and both the shaft and the bearing seem fine, but I bought a new bearing bush anyway. I was a bit surprised to find that the existing bushes are drilled through to connect with the oil cups, given that it was my understanding that these bushes are essentially self-lubricating and I’d assumed the oil cups were simply to keep them topped up. If I put in a new bush, should I drill it?

I would drill it, I am a great believer in lots of nice clean oil be it for a machine or an engine.

My lathe is the same. The strange thing is that if I top up the oil cups and run the lathe in forwards, one bearing immediately sucks up the oil and the other throws it out of the oil cup. If I top up the cups again and run in reverse, the first bearing throws it out and the second sucks it up. Very odd. Anyway, as these are self oiling bushes, they should run for years without needing replenishment. I now do it once every six months or so and don't worry about it.

Andrew M

Norman, are you sure the old bushes were Oilite, I wouldn't be surprised if they were plain bronze. With the Oilite bush plug the hole. In a Boxford A that I seem to be in charge of, the counter shaft runs in the cast iron of the counter shaft frame, and is lubricated with grease.

Ian S C

Ian

The bushes in question on the Super 7 were originally specified as "Oilite". What may have been changed over the lathe's life is another matter

I have a S7Plus and mine is the same, I top up both cups every time I use the lathe the right one swallows oil more than the left.My other lathe is a S7 mark 1 and that needs an oil gun but still reqires more on the right.

Frank

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In my opinion, Norman, your understanding was correct; and the answer to your question is NO.

At the risk of being ridiculed for debating 'How many Angels?' ... let's try thinking about this:

• Oilite bushes are engineered to retain oil within the structural interstices, and to release it gradually to the bearing surface.
• Capilliary action is involved in both aspects of this process.
• Between the rotating shaft and the bearing surface, there will be a small but finite gap [if the gap is large, something is already worn, and this analysis may not apply] which fills with oil.
• The shape of that oil-layer will, in reality, not be a 'cylindrical tube' because of side loads on the shaft. [it also differs in orientation, in the two bushes; producing the 'odd' behaviour]
• Rotation of the shaft, combined with surface tension of the oil, acts as a pump and draws fresh oil through the Oilite bush.
• Drilling the bush would change the dynamics; for the worse.

Over to the drillers, for their counter-argument

MichaelG.

My ML7 had Oilite bushings, with no hole drilled through them. From the state of them, it would seem they were factory original. So new ones were installed and left undrilled. One drop of oil in the hole in the casting every time the lathe is used is enough to keep them topped up without making a mess.

I wonder if it makes any difference though? Oil goes in the hole and if undrilled, enters the matrix from the top surface of the bushing and spreads from there throughout the whole. If drilled, it goes through to the gap between shaft and bushing and enters the matrix from there. Possibly more loss of oil out the ends of the gap in the latter method but in practice probably much of a muchness really.

So Occam's Razor and all that good stuff, I opt for the simplest way and don't drill the bushings. This also hass the advantage that swarf particles falling in the oil hole can't get into the moving parts, being held back by the matrix.

Edited By Hopper on 17/07/2018 10:01:50

In response to a similar enquiry of mine (but in a different application) on this board the weight of opinion then appeared to be:

Fit two oilite bushes of such length that there is a small gap (say 1mm) between them coinciding with the oil-feed hole.

I adopted this suggestion, which superficially to me at least, appears to exploit the characteristics of the oilite bushes and allows easy oil replenishment and 'top-up' without any drilling or machining of the bushes. It appears to work very well for me.

Regards,

Phil

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I think the difference is ...

Undrilled: The oil is drawn into the bush by the pumping action that I tried to describe.

Drilled: The oil goes straight to the bearing surface and is pumped out ... The bush then risks drying-out.

MichaelG.

Somewhat dubious as to the value of simply adding an undefined "oil" to Olite bushes. As supplied oil and bush will have been engineered to work well together over the projected life of the bush. Adding a different oil could well affect the flow characteristics within the bush leading to oil starvation making things worse. As with so many things steady development over the years has resulted in modern components having much better performance than older versions when used as per book recommendations. Flip side being that straying outside the book is often a very bad idea. Back in the day being inspector meticulous and careful about how you did things could often win much better performance in your specific applications. Not so much today. Its hard to beat millions of development hours!

Inclined to think that the "soak in oil before fitting a bush that has been on the shelf for a long time" are more about ensuring there is a local oil film on the surface immediately on start up than actually getting oil into the bush proper. Penetration into the bush is probably minimal so the proper oil soon drives out the added oil.

Always felt that a felt wiper between oil hole and a plain bush is much better than simply pouring oil into a hole. Especially Southbend countershaft style where a rectangular felt sits in a groove distributing oil all along the bearing. Steel on cast iron lasts forever so long as the felt is kept wet.

Clive.

Also, if the bush is drilled the oil and any contamination goes straight to the shaft, undrilled the bush acts as a filter.

Ian S C

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Clive,

I can't argue against that ^^^

But I would mention that Myford offered [as the politicians say] "very clear" advice regarding lubrication of the countershaft bearings, on pages 17-19 of the manual:

• Use ESSO NUTO H32 oil
• Replenish the two oil cups daily
• 'The hardened steel countershaft runs in oil impregnated bronze bearings which are located in the swing head. Oil cups are provided for occasional lubrication.'

MichaelG.

Replenishing the oil cups daily sounds like an awful lot of oil even if the originals are simple porous bronze bearings rather than what we know of as Oilite. Of course the $64,000 is what vintage is that advice.

At 64 as of last Friday I know only too well that things change over the years so, eventually, what you know ain't so anymore except for historical applications. Which can seriously catch you out if you haven't been paying attention.

As I understood things porous bushes needing regular oil feed came first giving self filtration, as Ian S C mentions, and better distribution without needing grooves as compared to simple plain bushes. I've always thought Oilite was a later development where the bush is able to retain a reasonable lifetimes supply of oil.

Clive.

I suspect the daily replenishment of the oil cups is for a machine in regular daily use for a fair spell of use each day, too much oil will do less harm than too little so a bit of mess can soon be wiped off.

Mike

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I beg to differ, Clive

Replenish means 'replace what is missing' ... and therefore could involve the addition of a minute volume.

Sorry but the document I have to hand is not dated. It does, however, mention that

UNDER I.S.O. SPECIFICATION 3448/1975(E) NUTO H32 REPLACES NUTO H44

MichaelG.

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This is worth a look: **LINK**

http://www.bowman.co.uk/news/a-brief-of-oilite-bearings

MichaelG.

As a matter of interest, are there any oilite bearings with lubrication holes drilled through them? Seems to me to be like expecting sealed bearings to be fitted with grease nipples....

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Well ... there's the two that are currently fitted to Norman's S7

[see the opening post]

But, I suspect that those have been 'improved' by some previous owner.

MichaelG.

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P.S. ... I should have said that you make an excellent point 

Edited By Michael Gilligan on 17/07/2018 22:44:11

You are right. I should have included the words ‘new’ or ‘supplied’, appropriately, in my post, to ensure that post-purchase modifications were excluded.