# Lathe Spindle Bearings (question) ?



## graham-xrf (Dec 12, 2021)

I have found several videos showing "scraping in bearings". The kind using blue, and working with a variety of small "curved up" scraper tools, sharpened along their sides. We see bronze split-bearings, and poured babbit bearings, being worked to perfection, but none so far about the plain bearing journals bored into the cast iron of the headstock.

South Bends, like my 9A and 9C, have the hardened, and super-finished spindles run in the iron casting bores. The bearing bores are adjusted on the spindle by tightening down onto shims mounted in a slot cut into the journal casting. They are supposed to run on a film of oil supplied by capillary wicks. The setup specification is there should be 0.001" to 0.002" indicator change when the spindle is "pulled up" from a position of being "pulled down". If figure from this that the clearance for the oil film to be there without problems is 0.0005" to 0.001".

My question is.. does one ever check out a cast iron bearing journal with blue, against a spindle, maybe with intentions of giving it the kind of scraping in to bearing surface I see done for the other kinds of bearings? Are the cast iron types ever scraped?

There seem obvious practical difficulties in even getting the blue mark on. One cannot simply lift the spindle off. Given that there has to be "clearance", I wonder there is any point in trying? That said, clearly the bronze types, also relying on oil film, are definitely scraped in.
Now that I think on it, I ask, would that be scraping for bearing surfaces fit, or "flaking" for oil retention?

Please forgive that the question seems a bit basic. This is something I simply don't know anything about!


----------



## C-Bag (Dec 12, 2021)

If I was going to try and figure clearance I’d use what I used for checking rod and journal clearance on engines called “plastigauge“.


----------



## graham-xrf (Dec 12, 2021)

C-Bag said:


> If I was going to try and figure clearance I’d use what I used for checking rod and journal clearance on engines called “plastigauge“.


Oh sure! There are various ways, but the one mentioned in the rebuild book is where you stick a steel bar up the spindle, and haul upwards, and also press downwards, while using a DTI on the spindle. I am sure Plastigauge, or stuff like it, can be found in UK, but measuring it is a separate question, and one I have also to get to soon.

It seems there may be scraping strategies designed to encourage oil from the place it arrives, into a slightly deeper scraped region, and so distribute onto bearing regions. Some bearings have a oil distribution slot along the bearing, but stopping short of the bearing ends, I suppose so as to not have it running out oil excessively. I read that plain bearings like this can be very accurate, and if given oil, can go for many decades without apparent wear. I guess that might apply to the spindle. I am not so sure about the cast iron journals.


----------



## C-Bag (Dec 12, 2021)

I’d use both methods just to make sure.

I could see honing a spindle bearing to fit, but scraping IMHO was never meant for the speeds a spindle runs at. And besides being hard to do(scrape a journal) it’s just going to wear out quick. If done right and with the correct clearance gravity fed oil delivery and oil wedge is more than sufficient to not wear out prematurely.


----------



## Weldingrod1 (Dec 12, 2021)

Cast iron journal bearings would be a "ream and lap" job in my book. The inner structure of the bearing is also important for load carrying and oil feed. It shouldn't be just a round bore...

Sent from my SM-G892A using Tapatalk


----------



## graham-xrf (Dec 12, 2021)

Weldingrod1 said:


> Cast iron journal bearings would be a "ream and lap" job in my book. The inner structure of the bearing is also important for load carrying and oil feed. It shouldn't be just a round bore...
> 
> Sent from my SM-G892A using Tapatalk


Hmm. A reamer for this would be all of 1+13/16" diameter chuck-side, and 1+25/64" the other end. Quite big tools!
I had wondered about lapping. Making up some aluminium ones would be OK - but here is where you need another lathe to fix a lathe.
It may be I need only clean up and put it together, but until I measure and inspect (with blue), I won't know exactly the shape of it.

That you say "it shouldn't be a round bore" checks in agreement with one Jan Sverre Haugjord, who has a video that does explain some of that. Unfortunately, I don't think he has one of any actual fixed journal scraping.

1. The recipe seems to be to scrape lower along the region where the oil channel is, but not all the way to the ends.
2. A "high region" is left at each end, looking to be about 0.15" or so, all the way around.
3. There are two further "low runs" along the length of the bearing, like sort of "passive oil distributionn channels", but not actually being deep cut. They are just low enough to not show blue.
4. The above leaves three bearing regions showing blue, set about 120° apart.

The question remains - is this sort of stuff done to cast iron plain journals? So far, I have only seen it done to softer metal shells.
Even if one were lapping, the whole rigmarole to check it with blue is a bit intense. Not easy at all!


----------



## Weldingrod1 (Dec 12, 2021)

It's been too many years since I pulled the spindle on my previous Sputh Bend... sorry I can't offer first hand lathe info. 

Sent from my SM-G892A using Tapatalk


----------



## matthewsx (Dec 13, 2021)

The spindle in my Seneca Falls lathe runs well when it's tightened just about so....


----------



## matthewsx (Dec 13, 2021)

I work in a support role for a company that has many accomplished engineers, occasionally they ask a question that makes me wonder why it matters. As a practical person I find myself asking if there is actually a problem with the item in question, or if they simply wanted to know how close to perfection it could get.

Bottom line, every tool designed should have a specification it needs to meet in order to perform as required. If it is within that specification you are more than welcome to attempt to make it better, but it shouldn't be necessary for it to perform as designed.

I say this because I've learned the hard way that I'm not usually better than the folks who designed and built my tools to begin with. I tried once to improve the sight on my British 303 rifle which I was able to hit a can at 300 yards one time. 

I didn't make it better....

John


----------



## C-Bag (Dec 13, 2021)

matthewsx said:


> Bottom line, every tool designed should have a specification it needs to meet in order to perform as required.


SHOULD being the operative word. I’ve been waiting for Bob Korves to chime in here as his plain bearing B&S surface grinder has some crazy precise plain bearings in it that if failing memory serves me he got sorted where others couldn’t. But it seems way more precise than the OP’s lathe.

I would not be messing with the bearing until I knew there was a reason to mess with it. Dabbling in water color painting taught me the value of being able to recognize as good as it gets without it turning into a mess.


----------



## graham-xrf (Dec 13, 2021)

matthewsx said:


> I work in a support role for a company that has many accomplished engineers, occasionally they ask a question that makes me wonder why it matters. As a practical person I find myself asking if there is actually a problem with the item in question, or if they simply wanted to know how close to perfection it could get.
> 
> Bottom line, every tool designed should have a specification it needs to meet in order to perform as required. If it is within that specification you are more than welcome to attempt to make it better, but it shouldn't be necessary for it to perform as designed.
> 
> ...


I do understand being practical, and it's not that I desire to work it up to a specification way above where it needs to be.
I only end up asking the question because I start from a position of being completely ignorant about what _does_ matter in this context. I simply don't know what the norms are.

In this forum, there are likely to be folk who do know. They may have had to fix something totally wrecked. More often, they will have seen some wear, whatever, and known whether it is just not a problem. They will have some judgement on what is bad. Generally, I know that even apparently trivial departures from "running properly" are often the beginning of a more rapid deterioration.

When it comes to these bearing journals, even if they be in great condition, I cannot know that without at least checking. An adventure with blue is not fixing, nor "improving" anything yet. It's just the stage of good/bad news discovery. If it is found to be in a mess, I am likely to attempt a rescue which need not exceed the designer's dreams - but it might, if I have no idea where to stop!

As to "improving" on already designed stuff, I have done it all my life! Most stuff I engage with, sooner or later, shows me a feature I would like to "design out". 

[Edit: Thinking on it, that info about up/down play clearance for oil is not actually a "specification" about bearing area. Actual numbers about stuff like that were probably not available outside the factory, even in it's heyday! ]


----------



## graham-xrf (Dec 13, 2021)

I eventually found some real close-up video of the nitty-gritty on scraping in a complete circular journal, as opposed to the split-block types. This one looks to be in bronze, but you can see the oil channel, and the detail of the tool technique.

That this trick exists at all, and seems documented, starts to convince me that my original question was somewhat justified. Folk do this stuff, though possibly, the original manufacturer might not have.

Scraping in a Myford MG12-M cylindrical grinder / part 7 (the end)


----------



## Weldingrod1 (Dec 13, 2021)

AH! Tapered bearings! Makes much more sense now!

Yes, that multi-zone bearing is the way to go. The scraper's 0.0001" metal removal is what you are looking for on clearances.

Sent from my SM-G892A using Tapatalk


----------



## graham-xrf (Dec 13, 2021)

Weldingrod1 said:


> AH! Tapered bearings! Makes much more sense now!
> 
> Yes, that multi-zone bearing is the way to go. The scraper's 0.0001" metal removal is what you are looking for on clearances.
> 
> Sent from my SM-G892A using Tapatalk


I thought that too - at first. The truth of it, I think, might be more subtle.
Since way before taper rollers were ever around, it was known you could have a spindle with run-out too small to properly measure, all held in plain bearings adjusted "just right". Here I now learn the four bearing zones support a film of oil, and everything else in there is about maintaining the oil layer. Hydraulic fluid dynamics - or something, but the oil in that confined layer can take a large sideways pressure, and not allow the metals to contact. The internals may be cut to within 0.0001" tolerances, but the oil layer is over 0.0004" each side. Fortunately, it's a stable layer, and it would not establish unless the bearing surfaces matched the journal really well.

There are limits, and a large enough load would probably defeat the phenomenon. Bigger cuts, larger work, higher speeds, and the like, would need something like taper rollers. Modern matched pairs of offset taper roller spindle bearings with built-in thrust pre-load would have their day. Plain bearings can match their accuracy, when run within their design capabilities.


----------



## Grendel (Dec 14, 2021)

my take on this is if you have wear in your split bearings, this is taken up normally by removing the shims and putting thinner ones in, so to my way of thinking all that should really be necessary at some point when the wear means that a shim is no longer needed, then maybe take a skim cut off the mating face of a bearing half shell to take up the wear, scraping is only going to remove more metal.
I think the proper procedure involves skimming the shells and bearing faces then reboring the hole to the correct diameter.
My Southbend has split shells with bronze inserts, its 100 year old and yet I can still manage to tighten the spindle bolts to the point that it locks the spindle, which says to me that its not worn to the point any adjustment is required yet.


----------



## graham-xrf (Dec 14, 2021)

@Grendel  Agreed!
Looking at the condition of mine, the 9C bearing surfaces looked smooth and slightly shiny grey. I would have thought, nicely "run-in". There was a shim clearly added after manufacture, probably by the previous owner, and perhaps needing a change. It's too thin!

The 9A is a different story.  It had clearly been left standing without rotation, long enough for a corrosion pitting to happen showing where the hole in the cone pulley was against it. I stoned it to remove any high spots, but the mark remains.  The bearings are OK (I think).


----------

