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seals for mini lathe tapered roller bearings?

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Martin of Wick01/04/2019 12:00:51
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Having had a knock down - drag out fight with my Chinese mini lathe to get the spindle and bearings out of the headstock, it occurred rather belatedly that the TRBs I was about to fit would be completely open with no protection (very much a Doh! moment). The carefully applied grease would puke out of the bearing fore and aft and every species and class of swarf, abrasive dust, moisture etc would pile in, cue dead bearing in short order.

Scouted about on the web and could find very little discussion of this particular, rather embarrassing elephant in the room from those that wax lyrical of the subject of bearing replacement.

Question is to those who have opted for this mod - what, if anything, can be done to resolve this problem ?

I can think of various solutions but all seem to involve significant extra work and expense in making new or modifying the bearing covers to accept rotary seals on the external bearing faces. Cant think of any solution to seal the back of the TRB so lubricant will be ejected into the headstock cavity no matter what- the existing headstock has most definitely not been designed for TRBs.

I am hoping there might be a simple, cheap, reliable, fix but I suspect that the choice will be restricted to two of the above. My possible quick fix may be to chuck the TRBs into the roundtuit box and go to sealed angular contact bearings (cheap and simple). Would prefer to use TRBs if there was a reasonable solution though.

Would certainly welcome others experience and solutions with this irritating problem.

Martin.

AdrianR01/04/2019 12:22:50
272 forum posts
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Sealed TRBs? **LINK**

Neil Wyatt01/04/2019 12:54:07
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I just turned the existing plastic covers so they would fit with the roller bearings in place, I can't remember exactly what I had to do but it was fairly obvious looking at the job. Over many years I haven't had any problem with swarf getting past them to the bearings.

Also don't pack the bearings solid with grease, best only to fill about 30%. This should also avoid significant squeeze out of the grease.

Neil

Edited By Neil Wyatt on 01/04/2019 12:55:56

Neil Wyatt01/04/2019 13:06:21
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I found this from when I wrote up my bearing swap:

"It is now possible to remove the 45-tooth bull wheel, wangle out its key and remove the long plastic spacer, followed by the plastic bearing shield which is held in place by three cap head screws. The two ends of the mandrel are covered by these plastic bearing shields. I found that I had to recess the inside of the bore of each shield by 2mm to clear the inner races. Unfortunately this only came to light once I had swapped the front bearing. I therefore had to recess the front shield by hand using a burr in a mini drill. An alternative is to recess the rear shield before removing the mandrel, swap it for the front one at the appropriate time, and recess the other shield when the mandrel is re-assembled. Unfortunately, to do this you will have to temporarily replace much of the drive gear. Whichever way you decide to proceed, the front shield will also need to be released before the mandrel is extracted. This is easily done by poking an Allen key through a hole in the mandrel flange."

recessing shield.jpg

moly grease.jpg

Niels Abildgaard01/04/2019 17:49:33
236 forum posts
74 photos

A Boxford headstock drawing.

There was about 0.05mm clearance between staionary headstock parts and rotating spindle parts.

It was part-filled with grease from factory and sold as Sealed and Greased for life needing no further attention.

Mine worked fine for ten years on two teaspoonfull of grease.

The drawing shows a very early model.There is two things that look like contacting felt rings.

There was neither felt rings or cut outs for them in my lathe.

 

Boxford A spindel.jpg

Edited By Niels Abildgaard on 01/04/2019 17:54:17

Edited By Niels Abildgaard on 01/04/2019 17:58:41

XD 35101/04/2019 18:05:53
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I made new ones from aluminium and fitted a lip seal - was it worth it ? Normaly no but the,plastic ones were cracked so i had a choice of but new plastic units or make my own . I have also cross drilled from the rear of the headstock and fitted grease nipples ( zirk fittings ) so i can easily grease the bearings without disassembly the grease is forced in between the bearing and seal and exits through the bearing and into the cavity in the headstock.

My other lathe just had a steel disk on the spindle that sat in a recess in the headstock separating the bearing from the outside world and in 15 yrs of use and abuse i never had a problem with swarf or dust getting into the bearings.

Ifyou were going to run flood coolant then I would look at something like lip seals or felt wipers .

 

f96f5c22-cf45-4678-84ab-6b90951234a1.jpeg

Edited By XD 351 on 01/04/2019 18:14:44

Martin of Wick01/04/2019 18:30:22
93 forum posts
4 photos

Thanks for that Neil, Adrian

as you say did notice as a minimum, the bearing covers will need to be relieved slightly to make space for the TRB roller cage. Still leaves quite a big gap, but apparently this does not appear to be as big problem as I imagined (visions of loose tools, dogs and small children, etc being sucked into the exposed bearing). Just still feel queasy about exposed bearings.

It is possible that oil seals of 48x60 would probably do with some further modification of plastic covers, but the covers are 8mm thick and the thinnest seal I can find is 7mm. Similar solution, differing sizes on the internal faces. Perhaps this is overkill and quite expensive at about £5-6 per seal.

There is a possibility that a 48 x3mm O ring could be used if the external cover was adapted a bit more - not a seal as such, but would minimise the gap on the external faces and help keep out coarser muck. Partially shielded TRBs are also available but I have not located any at the required size (at a price).

Think I'm leaning to cheap ACBs as a trial/quick fix while I ponder the requirement for TRBs long term.

Martin.

Martin of Wick01/04/2019 18:43:14
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Neils,

Thanks, as you point out, the Boxford was properly designed from the start for TRBs - so no issues. Fitting TRBs to a Chinese mini lathe is a kludge that raises a whole bunch of issues, unfortunately not a simple 'drop in' solution as is often presented .

In practice, need to be looking at a solution similar to XD351 if wanting to use and protect MTRBs long term.

Michael Cox 101/04/2019 20:21:38
515 forum posts
27 photos
Posted by Martin of Wick on 01/04/2019 18:30:22:

There is a possibility that a 48 x3mm O ring could be used if the external cover was adapted a bit more - not a seal as such, but would minimise the gap on the external faces and help keep out coarser muck.

This is the approach that I used when I did my taper roller conversion. I figured that at the very least the o-ring would act as a thrower ring and prevent oil and swarf migrating along the spindle shaft. I did the conversion at least 6 years ago. Every year I remove the plastic endcaps and inspect for debris. I have never found anything after the o-ring.

Martin of Wick01/04/2019 21:36:58
93 forum posts
4 photos

Michael, thanks.

That is interesting, can I ask if you modified the end caps to accommodate the O ring, or just 'squished' them down on the O ring and let them wear their own groove in the cap if needed?

As a supplementary, when you inspect the bearings, does it look as if they have retained their grease reasonably well, or does it look as if the lubricant has been thrown out of the back of the bearing? - I assume if the latter is the case, you take the opportunity to try to squeeze some extra grease in somehow before replacing the caps?

I suppose if the headstock fills up with grease over time no harm done as it can be scraped out and recycled to lube the gate hinges or garage door etc!

Thanks,

Martin

Michael Cox 101/04/2019 21:42:24
515 forum posts
27 photos

Martin,

I do not remember having to do any work on the end caps, but it was 6 years ago. I will have a look tomorrow and give you an update.

Mike

Martin of Wick01/04/2019 21:56:16
93 forum posts
4 photos

XD 351,

I have been studying your picture, but can't quite grasp it.

I get the new end caps, I see the black ring in the end cap which I guess is a rotary oil seal of some sort.

My question is regarding the black cylindrical object on or following the 40mm spacer with the circumferential grooves that apparently passes through the oil seal. Is it also some sort of rubberised sealing material, or just a piece of metal turned to fill the void space and allow a semi labyrinth effect? Does it sit on the spacer, or follow the spacer so it is compressed by the spindle nuts (if soft)?

Thanks

Martin

XD 35102/04/2019 00:51:32
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1326 forum posts
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Its the drive pulley , if you click on photos under my avatar you will find a file  named C2-2 there are more photos in there on the set up.

Edited By XD 351 on 02/04/2019 00:53:45

oldvelo02/04/2019 00:54:54
156 forum posts
43 photos

Cut them from a brass or plastic shim or any thin flat plastic

john carruthers02/04/2019 09:10:51
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I read that the original mini lathe design was of Russian origin and used TRBs. The later Chinese version used ball races.
Maybe an old drawing could be tracked down?

Neil Wyatt02/04/2019 09:52:20
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Posted by Martin of Wick on 01/04/2019 18:43:14:

Fitting TRBs to a Chinese mini lathe is a kludge that raises a whole bunch of issues, unfortunately not a simple 'drop in' solution as is often presented .

I think 'kludge' is more than a bit unfair. It brings many benefits and the only challenging part is the actual bearing swap, additional work required is minimal. The only other modifications are relieving a bearing cover and shortening a spacer.

One little mentioned benefit is that it moves the spindle flange a few mm further from the headstock making chuck fitting much easier, while, counter-intuitively, reducing the spindle's overhang.

Neil

Martin of Wick03/04/2019 00:59:16
93 forum posts
4 photos

Yes well, as you say Neil, a bit unkind but having had such a struggle to get the spindles out and bearings off I wasn't feeling kindly disposed to the little tinker. The front bearing removal took 2 attempts with the hydraulic press and came off eventually with a hell of a bang!

After much spindle and counter shaft polishing I can now put the new bearings on with only a gentle press fit, then replaced the nylon spindle gear with metal, left the countershaft with the nylon gear.

skimmed the bearing covers to accommodate the new bearing and put a slight chamfer on the front cover to allow it to mate with O ring used to seal the gap between spindle and cover. Will leave the back open for the time being pending trials.

I hope TRBs will be a worthwhile mod, and as you say, there is only a modest amount of work involved for a basic set up, but it is not trivial work and it does take quite a time. It looks like the O ring trick to fill the space between spindle and bearing cover is viable. There is a little bit of friction, but I expect that will ease with use.

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