Spindle problems: Potter bench lathe

[jim rozen]

Working on an older Potter bench lathe and the sindle has a bad oil control issue. The oil cups will keep oil in them for days as long as the spindle's not turning. I recently (finally) rigged up a motor and coutershaft, and the oil is pumped out of the bearings in minutes - rear bearing worse than the front. These are dual-angle cone bearings and the oiler cups are original I believe.

I don't understand the triangular grooves on these - top and bottom, both bearings.

Any suggestions to investigate?

 

[jim rozen]

Remaining photos:

 

[JST]

With just the one pic of the oiler, it's a little hard to be sure, but I would expect that the oiler was supposed to have felt in it, which would retain the oil and somewhat meter it out. I'd have expected to see a tube up the middle, and a felt "rope" coming up out of it and dipping down into the oil outside of the tube.

The spring-looking piece in the last pic reminds me of other machines here that have a spring lightly pressing felt against the journal. With those, the felt is supposed to be saturated with oil, which it then supplies slowly to the journal. That spring looks stiffer than I am use to seeing, if it actually is a spring.

One old fan has two similar setups, but upside down from that. The felt goes up the middle of the spring, but it is not pressed hard, just held by the spring. The reservoir has a screw thread that pushes the felt and spring upward, like a grease reservoir, but much smaller.

 

[Joe Michaels]

Jim:

This is a WAG on my part. In the last photo, the cap of the oil cup is shown partially raised. There is a compression spring inside the oil cup. Could there have been round felt wicks inside those springs ? This would act as a 'choke' and meter the amount of oil dripped to the bearings. While the oiling, from what I see in your photos is total loss, the wicks would reduce the oil flow to the bearings. The trick is to get just enough oil into the bearings to maintain the 'wedge shaped film' without flooding the bearings. Being a precision bench lathe with close-clearanced plain bearings, it would not take much oil to establish & maintain that 'wedge shaped film'.

Southbend accomplished something similar with spring-loaded round felt wicks, and relied on capillary action to move oil up to the bearings/journals. In the case of your Potter lathe, gravity provides the means for the oil to flow, and the wicks would serve solely in a 'choke' or 'metering' mode. There was some old wisdom associated with felt wicks used in this sort of lubrication system. Namely, the wicks served as a final filter for oil going to high-precision spindle bearings. Most particulates suspended in the lube oil will be filtered out by the wicks. Speaking from experience around the powerplants, we used to get DTE series oils in 55 gallon drums. It was quite common to find a bit of particulates settled out of the oil at the bottom of some of the drums. We had a portable oil processing unit which used a vacuum tank to pull moisture out of the oil, a heater, and a series of progressively finer filters. This was oil used in babbitted hydro turbine bearings, which, given their size/clearances, may as well have been giant precision spindle bearings. Back in the good old days, clean lube oil, particularly if transferred from barrels or cans and stored in a shop's lube oil dispenser, then into oil cans, may never have been really clean. With the kind of bearings on the Potter lathe, even a little fine grit could wreak some real damage. I'd look in McMaster Carr's catalog for round felt wicks and see if they have something that fits in the springs on the oil cups.

 

[jim rozen]

To the best of my knowledge the oilers never had a wick/riser tube setup. This is the one bit I have not had apart - but it's possible there
was supposed to be a felt in the oiler base. At first look the springs only hold the cover down tight on the oil cup. If there were a wick inside
the spring it would probably not do that job. But possibly in the base... The spring in the photo is an *extension* spring, not compression. I've got a pair of hemostats holding the cover open so I could shoot the photo down inside.

I also wonder if the wedge V-shaped grooves in all the bearing shells possibly had felt in them? Or if the brass covers that fit outside the bearings had felt seals on them? There was some debris inside the grooves which I've since cleaned out. The similar lathe I own of this vintage also has hard steel conical bearings but no oil grooves of any kind on them. Although that machine has a cylindrical rear bearing.
I blued the outer and inner cone of both bearings, and there's good contact between the shells and the inner pieces. I really don't understand the lower oil groove on these, they would only serve to pass oil from the small angle cone region, to the large angle outer areas.

I purchased this lathe at a junk shop in Wappingers, and it was missing the tailstock, which I've since made up from an old southbend unit. It takes 4Cs right in the spindle, and while the bearings *look* nearly perfect, and feel perfect when spun by hand, the oil issue is a killer. I'm not really running it fast (the motor pulley is quite small) but it pumps the oil out like crazy. I was hoping to second this machine to my daughter who's recently bought a house....

 

[JST]

The grooves are for oil distribution. It seems a little odd that they are triangular, and come so close to the front thrust bearing edge, but otherwise they seem pretty normal.

The triangular shape may distribute oil a little more evenly over the area it is needed. And the setup seems made for oil supply that is externally metered, not an "oil flood" system.

That is another indication of a missing oil metering arrangement such as Joe M and I suggested.

How sure are you that those are the original oilers? They do appear like they are. The Rivett 608 that I am working on has drip oilers for the same type bearing. However, if supplied with felts, the oil would be metered in a similar amount as with a drip.

Those bearing retain oil more than one might expect. But yours, with the grooves, seems as if it would "scrape off" oil and redistribute it in a different way. The 608 does not have any lower groove, only an upper one.

I mssed the fact that the spring was holding down the cover. But I don't know that it would change the idea of felt. Triangular grooves would tend to press felt outward, but I cannot see there being felt in the thin extension to the rear. Possibly in the front.

Where does the hole in the lower groove go? Is it just for a locating pin?

 

[jim rozen]

Yes, a locating pin. It lines up with the oiler port in the top of the shell, so it probably was assembled by pressing in from the interior of the bearing through that hole. I just took the oilers out, and theres no way there was a felt in the port at their lower part - the spring is retained at the bottom by a loop of steel wire that exends out the bottom. So the assembly for those was a longer hairpin of wire has the spring captured, the the wire is passed through the lower hole, the ends bent sharply out to the sides and cut off shorrt so they clear the ID of the 1/8 NPT port in the casting.

The oilers are apparently cast bronze and have the designation "00" (zero zero) and an "L" inscribed in a circle on the wrench flats. Most likely Lunkenheimer. They were only installed in the headstock casting *very* loosely. I wonder if air being allowed into the top of the oil column might make it flow faster out of the bearing.

I'm going to dismantle these so I can clean them well, one had a bit of sludge in it. Will photograph the parts.

Oil BTW has been 0W20 mobil one.

 

[jim rozen]

This is basically the lathe - although without the original TS:

Potter lathe

Oilers similar, but not the same from what's visible.

 

[JST]

Yes. The ones in the pics appear to have a knurled cap, which would seem to suggest they are threaded. That in turn would probably allow felts of some type, either in the feed, or coming up through a tube, and over into the oil.

Or, these might be the same sort of deal as what you have, just with a different cap. It does seem that they might run through oil pretty fast.

However, my small Boley has absolutely no reservoir at all. It has small brass/bronze rings with slots that can be turned to let you drip oil into the bearing, or to block dust etc from getting in. No felt, no reservoir, seems to just rely on the oil held in the bearing itself. It works fine. Oil seems to stay in the bearing fine through at least the time to make a part.

I have no idea if it has any oil distribution grooves.

 

[jim rozen]

Possibly the answer, yes. After the oilers ran dry, I ran the machine for a half hour - there was a constant film of oil around the edges of both bearings, and there was no slowdown or heating at all. On shutdown the spindle was free and felt smooth.

 

[IrbyJones]

I can't offer any opinions on this except to say the Stark #3 and #4 lathes had the same basic design for the spindles and headstocks. I have an old #4 headstock here and it has the V groove in the bottom of the front bearing just like this one. When I took it apart, there was just crud in it, nothing like any felt like I would have thought. Although the steep taper of the groove wouldn't hold the felt very well. Rather than upload a new picture of the front bearing, I found one already posted by aninventor back in 2017 when asking about spindle speeds for a Stark #3 headstock:

Spindle speeds for plain bearing headstocks - Stark

So maybe someone with a Stark #3 or #4 lathe could chime in with a comment. The oiler on the lathe aninventor had looked like this, if it's any help.

Irby

 

[MrStretch]

I have a Stark #4 that has oilers like the one above. No trace of any wick or felt. I've always just filled them up before using the lathe.
The Mobil 1 might be part of the trouble. Did you try a light spindle oil?

 

[MrStretch]

Maybe the groove is meant to work in conjunction with the knurled brass cap or cover to act as an oil reservoir? I think the spindle end caps are important as they help seal the outer joints of the bearing.

 

[esbutler]

I wonder if it has little to do with the oilers or the grooves. What if the steeper taper bottoms out before the shallow taper (either due to a bugger on the seat for the steep taper or excess wear on the shallow taper) and the shaft bounces around enough when turning that it essentially milks the oil out?

 

[jim rozen]

Thanks for all the comments.

1) I've tried a variety of differerent oils, including Gen-U-Wine southbend spindle oil (basically DTE light, or 'turbine' oil), 5 wt ATF, and the aforementioned 0W20 mobil one. They all behave the same as far as operating well in the spindle for lube, and the same in terms of how rapidly the oil reservoirs empty. More and more I'm suspecting the only reason the bronze cups are there is to make it easy to give it an occasional shot of oil and the covers are there to keep junk out of the bearings.

2) the bearings are indeed double angle type, a sharp taper at the ends and a gradual taper on the interior. I blued them up and lo and behold all the bearing areas are in full contact. It's a highly over-defined geometry but they did it right so all angles contact fully. Amazing.

3) I have gone and put the brass knurled cover rings in place, and this does not seem to slow down the pumping rate.

4) I've also gotten a much larger motor pulley which means the spindle is moving a good deal faster, and does not heat to any great degree
at all even after 1/2 hour operation with the oil cups emptied, but again with a film around the periphery of the spindle on both ends.

I've taken to setting the clearances on the bearings by measuring the axial play, at this point the total play is around 0.0007 and 0.0008 inch. Basically just push the cone pulley to the rear, zero the dial gage (held in the tailstock) and then pull forwards and read the total reading. This all seems to work well.

At some point the next job is a small three phase motor and a VFD as the present motor is working pretty hard.

 

[MrStretch]

Interesting. I wonder if the bearing clearance has anything to do with it. I adjusted my stark just like a watchmakers lathe - adjust the take-up ring on the back until the spindle moves without any binding.
I asked about oil because I tried Mobil 1 and the headstock was noticeably warm so I switched back to 3-in-1. I think the oiling cups on the stark are meant to work by capillary action drawing the oil up & over into the central tube. It drips all the time, no need to worry about changing the oil.

 

[MrStretch]

The more I think about it, shouldn't the bearings provide some sort of back pressure for the oiling? The oil draining while it's running suggests that there is maybe too much clearance?
Here's how I was trained to adjust the bearings on a watchmakers lathe- tighten the adjuster on the back while rotating the spindle by hand until it starts to bind. Now, carefully back off the adjuster until it turns smoothly. It is adjusted properly when it's on the hairy edge. The brilliance of the design is that as long as the bearings aren't worn oval or heavily scored, they can be adjusted and will run true, or true enough for a clockmaker that doesn't have any dtis or anything.

 

[jim rozen]

I did the 'tighten till it binds then back off a bit' approach and measured that - it was just about one thousanth clearance. I snuck up on the 8 to 7 tenths number.

Agree that a normal plain sleeve bearing like that should develop a hydrostatic wedge - but with the two large wedge-shaped grooves, those might intercept that? Another point is the iron headstock casting will have a larger thermal expansion than the steel spindle - so as things warm up the clearance will increase, so it's self correcting for bearing snugness to some degree.

 

[MrStretch]

Sorry Jim, out of ideas. In 12+ years of use, I've never had the headstock apart, but l would presume that it has the same grooves as the stark pictured above.
These old bench lathes are absolute marvels, I'm sure you'll figure it out.

 

[MrStretch]

I lied, not completely out. If my comment about the existing oiler on my lathe using capillary action to draw oil into the bearings is correct, then the oil consumption would be independent of whether the lathe is running or not. The center tube from the oiler cup into the headstock is open, so there is no atmospheric or oil pressure forcing oil into the bearings.l