Twin Engineering’s heavy mill/drill quill removal

[PeteParticipant @pete41194]

Old seals that have degraded and lost there flexibility will even rub grooves into hardened shafts. It takes awhile, but they can do it. And I’ve seen that happen many times. But if seals were used with the manufacturers original bearings, then there was good reason to do so. Unless it’s on something specialized and well outside what any machine tool would use, no machine tool bearings are designed to run that hot that you can’t keep your hand on the outer area of where they are. The grease or oil lubes were usually using will begin to break down if that temperature starts getting over 120-150C. And all that excess heat probably helped a lot to kill those seals anyway.

Any greases or oils are NOT equal.I spent most of my career dealing with and having to use lube products for some of the largest open pit mining equipment that’s made on a daily basis. Any grease or oil that’s handy or available isn’t what you use. Especially if those bearings are creating far too much heat. Something is guaranteed wrong. Either the incorrect use of grease verses oil or visa – vis. Excess bearing preload etc. Either grease or oil might be correct, but which grade and type of grease or oil is just as important. You need to accurately measure with indicators how much radial and axial play there is for preload when cold as your base line starting point. But I’d first contact the bearing manufacture, tell them what the bearings are being used in, maximum rpm and ASK what the proper lube should be for that specific bearing and use, how many mls of grease and what exact type to be packed into each bearing if grease is the recommendation, or what specific oil and how often is to be used. Then ask about bearing preload and the minimum amount of axial preload clearance before bearing damage. They may even still have old records from the original mill manufacturer and what they recommended to them at the time when these mills were still being produced. Doubtful maybe, but you can’t know that for sure without asking.

In general, that preload and just how tight can usually be estimated if the bearings are starting to get hot, but you can’t even do that if the heat is being caused for other reasons. And bearing heat temperature stabilization usually requires at least half an hour at continuous rpm to then be certain the temperature has stabilized to it’s maximum operating temperature. It cost me over $800 to learn I’m not smarter than the manufacturer’s lube recommendations while paying for a very expensive European manufactured lathe motor replacement. The wrong, too thick and heavy oil was a full on Dunning Kruger level mistake, and no one but myself was at fault. And if the incorrect lube was used and the seals are old enough to be causing any issues at all, I’d just replace the bearings and seals with brand new no matter how good the old bearings look. There’s obviously no new spindle or bearing housing parts available anymore, so you can’t afford to play around at all. You solve problems like this by using basic logic, some known facts about lubrication, and not guessing.

 

[Clive FosterParticipant @clivefoster55965]

Having made a similar error, albeit not quite so costly, I know Pete is absolutely right about the need for correct oils in highly specified applications.

But the Twin is a product from a small manufacturer made to a satisfactory, workman-like specification so one would expect a common, normal for the period in such applications, oil or grease to be satisfactory. If, as had been suggested, most sales went to educational or small workshops needing a not too expensive mill of decently useful performance its extremely unlikely that the maker would have specified an uncommon lubricant.

Martins idea of a teflon labyrinth seal is good but it’s quite practical to make a basic light contact single lip seal. I found stopping the material running away from the tool on the thin section was bit tricky but I managed it. Once! Never again.

I’ve just done a two lip labyrinth in delrin for a modified motorcycle speedo drive that seems to be working well. I’d have preferred more lips but no space. Machined to nominal gnats eyebrow under zero clearance with a touch of drag it settled back to free running but no perceptible clearance after an estimated hour or so of running. Stripped for inspection after 300 miles running, looks good for many thousands more.

Clive

[PeteParticipant @pete41194]

Nope I don’t think the mill manufacturer would have specified anything unusual Clive. But almost for sure they would have consulted with the bearing manufacturer before finalizing the design and lubrication type. Then almost for sure they would have run long term operation tests. That I think would non optional just to not have problems with future warranty claims. So to me, finding out if it’s oil or grease, how much, and which specific weight and type would be the first place to start. Properly installed, lubricated and with the correct preload. Spindle bearings don’t create that amount of heat unless one or more items are incorrect. That should have been the first warning indications.

Moore Tools in the U.S. used quite complex spindle bearing installations, and the heaviest amounts of preload I’ve ever read about with no reports of excessive heat from the bearings on there jig borers and jig grinders. That high preload did result in less lifespan from the spindle bearings, but it was there chosen method to get the spindle rigidity and accuracy they wanted.

[old martParticipant @oldmart]

As already mentioned, the spindle is basic like our Tom Senior and the round column mill, just two taper rollers and modest rpm. When it was common for cars to have a pair of taper rollers on their front stub axels, it was normal practice to do up the nut to a couple of foor pounds and then back it off a set ammount, in my car it was one flat of the hex nut and then lock it there. This prevented heat from braking from overloading the bearings. My experiance with Castrol LM grease is it seems to hold the record for oil separation over time, other brands are not so oily.

My firm used to manufacture transfer machines for car makers. A part would start one end of about 20-30 automatic stations and come out about 200 feet along the line with most of its machining completed. The machines were running non stop 46 weeks every year before being shut down for servicing during the 6 week shutdown in production. When the many spindle bearings were assembled, the fitters brought special Kluber grease to be weighed to the nearest 100mg so the exact ammount went into each set of bearings. I dread to think just how expensive that grease was.

Our Smart & Brown model A is at least 76 years old, with plain bronze bearings running directly on the steel spindle. We feed it 5W30 fully synthetic motor oil in it’s total loss lubrication system. I recon it’s better than any oil available when the lathe was new.

[Martin of WickParticipant @martinofwick]

I hear what you say Pete, but the Twinmill, for all of its doughty qualities is no Aciera, Schaublin  or Deckel. It is the product of a small company in the heroic age of British manufacturing – seat of the pants, finger in the air, hand and brain, time honoured tradition etc. I doubt if anyone involved with its design and manufacture ever bothered to shake a slide rule at it!

Yes, they would have consulted with a range of quality bearing providers, but only to get the lowest possible cost quote for supply and bearing manufacturers would have responded in kind – ‘Not for industrial or manufacturing use sir?, we recommend these open cup and cone taper roller wheel bearings, low cost, tolerant of setting and abuse, adjustable, easily lubricated…etc’ And the lubrication recommendation in 1960 would be ‘install with lithium grease sir’ with a cautionary ‘avoid overpacking’ just as it is today for this class of bearing with SKF!

No guesswork involved with solving the heating problem on this mill. Numerical and empirical investigation proved the bearings were just fine on their own, the killer was the oil seal generating about 70 watts of heat at 3000 rpm- imagine a 70 watt incandescent light bulb (remember those!) stuffed inside the nose of your spindle! It will warm up real quick!

As the bearing is an open cup and cone type, it would need protection from swarf, so as far as the manufacturer was concerned, an oil seal would be the simplest and cheapest approach. I doubt that potential heating issues from friction occurred to anyone at the time. If the customer latterly complained, the standard customer service response would be given ‘yes well, they all do that sir, you should really try to avoid running it at high speed….’.

Those prophetic words explaining one of the factors that condemned British mass manufacturing to its doom.

In the end, the bearings for this machine are just low cost wheel bearings, practically cheaper than dirt. If you are not squeamish you can have replacement Brand X for £10 a pair, if you want to go posh, a pair of SKFs or Timken can be found for less than £40. When installed, it is not practical to re-grease without dismantling, so lubrication will be 1ml of 140D to each bearing at the the scientifically prescribed interval of ‘once in a while, when needed’.

I can report that now the bearings have been run in for a while, even at highest speed heating is no more than lukewarm. No longer any risk of third degree burns from the spindle nose! I shall recheck when I install one of Old Marts cut down expertly modified oil seals.

 

 

 

[Nicholas FarrParticipant @nicholasfarr14254]

 

No guesswork involved with solving the heating problem on this mill. Numerical and empirical investigation proved the bearings were just fine on their own, the killer was the oil seal generating about 70 watts of heat at 3000 rpm- imagine a 70 watt incandescent light bulb (remember those!) stuffed inside the nose of your spindle! It will warm up real quick

 

 

 

Hi Martin, yes I can remember those incandescent light bulbs, and I’ve still got a dozen of each 60 & 100 watt unused ones, along with a really old 150 watt one that still works, all of which are Pearl ones.

The socket it’s in is quite interest, as it has an integrated switch, which can only be operated when a bulb is inserted, therefore you can’t get an electrical shock if you stuck your finger in it, if the light switch is left on.

As you can see, the two pins are mostly covered without a bulb in place, and both are disconnected from the electric supply.

It has 2A with T2 underlined with 250V ~ and BS EN 61184, and HS9696, moulded into the plastic. I’ve never seen one of these before.

Regards Nick.

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