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Timleech
07-20-2009, 12:51 PM
I'm trying to sort out some oil leaks on the headstock of my 'new' DSG lathe, there are leaks from around two shafts where they enter the headstock.
One is the 'overdrive' shaft which has a straightforward open bearing & separate Weston lip seal. The bearing is a bit noisy anyway, so I've ordered new bearing and seal.
The other leak is from the 'No1 shaft' (input shaft), this relies only on a 'sealed one side' (neoprene seal) ball bearing to keep the oil in.
Question is, is this a 'normal' arrangement, or is it being a bit optimistic to expect the integral seal to be adequate for that job? It's near the oil level, and there is a *lot* of oil flying around when the spindle is engaged, though to be fair there is another (open) ball bearing between this one and the 'main action'.
Subsidiary question, as single seal bearings are twice the price of double sealed, so the way to do it is buy a double sealed unit and knock out one seal, what if I put in a double sealed bearing? That would presumably reduce any leakage, but how long could I expect the bearing to last without a free supply of oil? It's running at 1200 rpm all the time that the lathe is switched on, 6308 bearing, carries the (substantial) tension of the main L16 Polyvee drive belt.

Thanks

Tim

Forrest Addy
07-20-2009, 01:06 PM
Bearing seals are only effective for retaining grease and excluding foreign material. They're not intended to seal against pressure of any kind, not even an inch of water column. A little external oil drool may stop at the seal but if there is any vertical head on the oil it will likely seep through.

Timleech
07-20-2009, 01:45 PM
Bearing seals are only effective for retaining grease and excluding foreign material. They're not intended to seal against pressure of any kind, not even an inch of water column. A little external oil drool may stop at the seal but if there is any vertical head on the oil it will likely seep through.

There is no actual 'head' unless pressure builds up within the headstock.
So far as I can tell it was designed this way and has been so for 35 years, but I might try to speak to 'someone who knows' tomorrow to find out whether they improved the design after mine was built. There's just about room to bore out the bearing retainer to include a seal to run on the pulley hub.
I think oil was cheap when they designed the lathe, the headstock holds 7 (Imperial) gallons, maybe they thought a few drops wouldn't be missed but it does make a mess, as well as getting on to the drive belt.

Tim

Evan
07-20-2009, 02:01 PM
In my experience the term bearing seal is an oxymoron.

tdkkart
07-20-2009, 02:15 PM
In my experience the term bearing seal is an oxymoron.

Quite, and more often than not the seals seem to do more to hold IN any contaminates that happen to enter, especially water.

My favorite seal issue is on the motorized right angle conveyor gearboxes. For some reason the brainsurgeons that design the conveyors always mount them so that the motor is below the gearbox. When the gearbox seal starts leaking it fills the motor with bearing grease.
I guess it's a failsafe, the motor stops working before the gearbox gets damaged.

lakeside53
07-20-2009, 03:21 PM
If there is room before the pulley, a common way is to screw on an external flange (only slightly larger then the seal) to hold a seal. If the shaft isn't "seal quality" at the point or some wacky size, use a sleeve. There are off-the-shelf sleeves called "jiffy sleeves" for repairing shafts worn at the seal points in sizes that will fit almost anything.

Knocking ("picking" is a better decription for rubber) out bearing seals is common. I often leave them in place until I'm ready to do final shaft assembly - minimizes the junk that can get into the bearing. If you leave both in place in a oil environment, they will leak and the oil will slowly remove the grease, but... you won't get oil back in the bearing at startup in the desired quantize. Take at least one out... If you put a shaft seal after the bearing, take both seals out - you need oil on the shaft to lubricate the seal.

You might find the existing bearing seal is just worn, and replacing it with a new bearing will resolve the issue. There are severl forms of seal - some of which are contact, light contact, no contact... A full contact seal (typical "RS" type) will general more friction, but at big lathe speeds, it's not likely to be a problem..

Timleech
07-20-2009, 03:27 PM
If there is room before the pulley, a common way is to screw on an external flange (only slightly larger then the seal) to hold a seal. If the shaft isn't "seal quality" at the point or some wacky size, use a sleeve. There are off-the shelf sleeves called "jiffy sleeves" for repairing shafts worn at the seal points in sizes that will fit almost anything.

The pulley actually clamps the bearing in place on the shaft, but it's a 'hollow' pulley with a 2.5" dia boss the same depth as the pulley itself. There's a very chunky bearing clamping piece, for the OD, which this boss runs inside, it should lend itself nicely to boring out to take a seal. It does seem a bit crazy, though, planning a mod like that on a high quality machine which has run without any such seal for 35 years!

Tim

lakeside53
07-20-2009, 03:39 PM
I might have added to my post after you quoted it...

I'm doing a similar thing on my "new" 30 year old Polamco. My motor mounts low, and there a shaft seal in the bearing retainer to stop gearbox oil getting to the motor. The seal has gone "hard" and has worn the shaft. I'm moving the seal retainer forward with a spacer to get to a new "wear point".


ha.. and just 'cos it's 35 years old doesn't mean they designed it right in the first place! I've added shaft seals to three bridgeport 6F drive motor now...

Willy
07-20-2009, 03:41 PM
Subsidiary question, as single seal bearings are twice the price of double sealed, so the way to do it is buy a double sealed unit and knock out one seal, what if I put in a double sealed bearing? That would presumably reduce any leakage, but how long could I expect the bearing to last without a free supply of oil? It's running at 1200 rpm all the time that the lathe is switched on, 6308 bearing, carries the (substantial) tension of the main L16 Polyvee drive belt.

I used to have 2, 10hp, 3600rpm motors that ran water pumps for years without bearing problems. Both motors used 63082rs bearings which were factory lubed with grease.
Oil being more viscous has a tendency to migrate past both inner and outer bearing races where they interface with the bore and shaft, unless the shaft and bore are free of nicks and scratches and the fit is snug. Sometimes a sealer applied to these surfaces makes all the difference in the world.

John Stevenson
07-21-2009, 03:43 AM
Subsidiary question, as single seal bearings are twice the price of double sealed, so the way to do it is buy a double sealed unit and knock out one seal, what if I put in a double sealed bearing? That would presumably reduce any leakage, but how long could I expect the bearing to last without a free supply of oil? It's running at 1200 rpm all the time that the lathe is switched on, 6308 bearing, carries the (substantial) tension of the main L16 Polyvee drive belt.

Thanks

Tim
Looking at it logically exactly the same amount of time that your main drive motor bearings will last given they have the same belt load and will be running at 1425 rpm.

[ Edit] Willy beat me to it with the previous post but depending on design can you fit a thick felt to the inner side to stop any oil splash soaking the bearing and washing the grease out.

However I think it's more a text book case as even in regular use Tim this lathe isn't going to be running 20 hours a week ?

Timleech
07-21-2009, 04:49 AM
Looking at it logically exactly the same amount of time that your main drive motor bearings will last given they have the same belt load and will be running at 1425 rpm.

[ Edit] Willy beat me to it with the previous post but depending on design can you fit a thick felt to the inner side to stop any oil splash soaking the bearing and washing the grease out.

However I think it's more a text book case as even in regular use Tim this lathe isn't going to be running 20 hours a week ?

Agreed it's not going to be working huge numbers of hours. I only want to do the job once, though, while I still have good access to the end of the lathe ;)
The idea of a felt ring might be a good one, I have some solid felt available.
Actually the main drive motor bearings are single shielded with spare grease the other side, & they're life expired which is what started me on this job. I'm sure it's done many many more hours in the past than it'll do in my ownership, though.

Thanks to all
Tim

macona
07-21-2009, 05:10 AM
In my experience the term bearing seal is an oxymoron.

I dont know about that. Bearing seals seems to keep crud inside the bearing quite well.

The rubber seals will seal OK up to the bottom of the shaft.

Yes, you can remove one of the seals with a small screwdriver. Just make sure you are careful and do everything in a VERY clean place. Clean your tools with solvent before using them to install the bearings

John Stevenson
07-21-2009, 09:03 AM
In my experience the term bearing seal is an oxymoron.

Unless fitted to Das Plank.

.

Timleech
07-21-2009, 09:43 AM
I dont know about that. Bearing seals seems to keep crud inside the bearing quite well.

The rubber seals will seal OK up to the bottom of the shaft.

Yes, you can remove one of the seals with a small screwdriver. Just make sure you are careful and do everything in a VERY clean place. Clean your tools with solvent before using them to install the bearings

When I said they could be 'knocked out', I didn't mean literally, with a mucky cold chisel and mason's lump hammer :D
I've ordered bearings, as well as a suitable seal which I might fit, still undecided. The bearing in question is at the outer end of a housing, maybe 3" long, with an open bearing at the inner end. Maybe the reasoning was that there wouldn't be a huge amount of oil coming past the first bearing and struggling to escape through the outer seal.

Tim