Machine spindle bearings - how delicate are they actually?

This is more or less idle curiosity, hence tea room. It's often said that whacking out MT tapers through the spindle bore is 'bad for the bearings'. Yet this seems to be the standard way of gettting them out on MT spindle milling machines which don't have 'self ejecting' drawbars. My wee Warco WM14 has a self-ejecting system, so I've never had to abuse it in this way, but I confess that I've had an MT5 stuck in the lathe spindle and whacked it out with a mallet - without any obvious ill effect. My car wheels presumably run on bearings ( I have no idea about cars!) and have managed over 100 kilomiles - bumping into stones and stuff (my wife is an atrocious driver ) - so must have been been subjected to much heavier loading than I could manage with a mallet.

I suspect that worries about knackering bearings by hitting them with a mallet blow might be unfounded, but I'd be interested in informed opinion. I have no 'gut feeling' for the forces involved.

Rob

Edited By Robin Graham on 23/08/2017 23:14:23

Hi Robin

Followed this subject on another forum and offered my solution.

No Bearings were damaged in these photos

LINK

Good question. Maybe it's more a case of pounding on a bearing CAN damage it, rather than WILL damage it. But if done repeatedly over time, sooner or later the time when it WILL do damage is sure to come up.

Certainly bearing manufacturers recommend very definitely against pounding on bearings. I'm sure they know their stuff when it comes to bearings.

Wheel bearings on cars are subjected to a radial loading, and are sandwiched between springloaded shock absorbers and inflated rubber tires, which is a different ball game from a direct hammer shock axially. You would never get your MT4 arbour out of a spindle if the spindle were mounted on springs and you pounded on the drawbar with an inflated football on a stick for a hammer.

How sensitive are roller bearings? I remember when there was trouble with bearings on large electric motors installed in the car factory I worked at in Australia. Turned out the problem was caused by the motors being shipped on a vibrating ship from the USA, with the motors laid down flat in their normal operating position. Weight of the heavy armature on the bearings, sitting stationary but vibrating from the ship's engine, put dents or flats on the rollers and races, causing early demise. So they started packing the motors to sit with spindle vertical for shipping and problem stopped. Weight was born on the ends of the rollers, which did not impact thier performance in normal use in the horizontal position. So it is possible to wreck bearings, or at least cause rapid wear, by simple mistreatment, for sure.

MOVED FROM OTHER THREAD.

I found this old post from 2013 and relates to the recent posts, M3 milling chucks and machine spindle bearings. On my sx2p mill I follow the procedure as stated by ARC, but also use a piece of wood supporting the area near the chuck when hitting the drawbar as to not strain the jibs on the Z axis. My point is when hitting the drawbar how will this affect the bearings on the mill, as stated on the post M3 collet chucks to be aware of damaging the bearings on the lathe this is the same procedure when I fit the stud drawbar.

Alfie

Edited By Alfie Peacock on 24/08/2017 02:33:47

Edited By JasonB on 24/08/2017 08:10:09

At the opposite end of the scale, it has been found that cleaning very small ball bearings in an ultrasonic bath to get the grease out prior to using them in clocks (where the grease viscous friction is not wanted and the loads very small), ruins the bearings.

People will always have anecdotes for bearing failure. I used bearings in rotating assemblies all my life and had few failures during normal life of the bearing, talking of three shift work in production environment.. In most cases failure will happen fairly quickly if all is not right. Design will take care of a few knocks, with correct or over sizing. For the work they do I think the small mill/drill bearings will take many hard tool withdrawals before failure. The cause of most failure is prolonged excessive load with incorrect lubrication causing heat buildup then metal failure in one form or another. Most car wheel bearings are now not separate ball bearings by merely balls or rollers between the wheel shaft and housing, hence the cost of replacements if ever needed.

I have a SX2P and don't worry about hammering the draw bar when necessary, and I'm one that overtightens in most cases.

MOVED FROM OTHER THREAD

Hi Alfie,

Like you I use a piece of hardwood between the table and the lower end of the spindle on my X2 milling machine when hitting the drawbar. As far as I can understand this procedure should not affect the bearings (someone with more knowledge than me will surely correct me), I also don't tighten the drawbar much so a light blow with a copper hammer is all that's needed.

Thor

Edited By JasonB on 24/08/2017 08:09:31

Edited By JasonB on 24/08/2017 08:10:34

Well my X3 is just over 11yrs old now and I change tooling several times a session by tapping the drawbar with a copper hammer. Only adjusted the bearings once when I got it and they are still running fine.

If you are not monkey handed when you do up the drawbar it does not need the living daylights belted out of it to free the taper. I tend to hold the tooling in my hand and tighten drawbar, you do see people adding spindle locks or long spanners on the spindle to hold it still, this I assume is to allow them to tighten the taper more than needed!

J

In the 60's i bought a SAAB 95 and was a nice car, in the snow I slid with the wheels slightly turned and hit the kerb. From then on as i went around a slight bend i could hear a ticking noise from the wheel hub.

I stripped it out and replaced the double row bearing (£10.00 in those days)that the steering turns on which was very easy and the noise was gone. Examining the bearing I could see indentations of the balls in the outer ring. Brinelling is the term I think?

This is akin to belting the lights out of a bearing in a machine and as stated by others the tooling should never be tightened so much you need a sledge hammer to release! The tapers make their own tightness and need only a light tap to release, I turn the spindle as I do it.

Clive

Absolutely right that over tightening is a mistake, but so is a loose grip. I started by hand-holding the tool on my WM18 whilst tightening the drawbar and found that the taper sometimes slipped whilst cutting.

As spinning the tapers will damage them, I now use a spanner to hold the spindle and finish off with a nip; up to 1/16th of a turn after reaching hand-held tight. The extra step may only be necessary because I don't have strong hands.

Dave

I prefer to hold the chuck when tightening, thinking a slip may be better than braking something. I was caught out by hand-holding an MT3 face cutter in my son's X2.7 though. When I came to remove it I found there wasn't enough clearance between cutter and spindle for the pin spanner, so I couldn't use the self-eject and had to resort to a copper hammer.

Brian

When I started selling engineering tools and machines some 17 years ago, I too thought that whacking the draw bar with a mallet would have adverse effects on the spindle bearings. However, I was proved wrong, as it has been extremely rare for ARC to supply replacement bearings as a result of damage caused by hitting the draw bar with a mallet.

If such an occurrence took place, it was usually due to over tightening, and/or use of a hammer in place of a mallet, combined with inadequate force being used... as if one was driving a nail into a piece of wood... slow and steady, instead of a short sharp blow with a mallet, and where the user would forget to lock the hear in place (probably not critical... but possibly a good idea... specially if the spindle has been running hot over a long period resulting in the MT fit becoming tight.). Where the fit has become tight - due to over tightening or heat, sharper blows may be required. Even so, rare to see replacement bearings being sold resulting from this.

Replacement bearings for spindles has been seen more due to people converting their machines to belt drive, where abnormal wear is seen on the bearing near the top of a spindle.

Ketan at ARC.

The only exception to the above could be high speed spindles... say above 15,000rpm for example, which use high precision bearings, where self ejecting systems would be preferred, and in most cases, such spindles would have tapers other than MT2, MT3, R8.

Ketan at ARC.

Edited By Ketan Swali on 24/08/2017 12:32:33

...As spinning the tapers will damage them, I now use a spanner to hold the spindle and finish off with a nip; up to 1/16th of a turn after reaching hand-held tight. The extra step may only be necessary because I don't have strong hands.​..

​Same here, I use a small 4" ratchet handle, to 'nip up' when I change tooling & just pull enough to 'feel' the tapers mate up.

George.

A few anecdotes.

1) In USA, at one time cars delivered by rail, (on Auto Racks) were found to have damaged wheel bearings, "Brinelling", caused by the vibration of running over the track. Setting the vehicles on their tyres, instead of standing them more or less up on end, solved the problem. The rubber tyres decoupled the bearings from the vibration; being, literally rubber mountings.

2) A particular Lanchester balancer, in an engine used to Brinell the shafts. It was found that: the key way for the driving gears threw the shaft slightly out of balance, and that the ratio of needle roller diameter to shaft diameter was an almost exact integer. This combination meant that a needle was regularly hammered against the same area of the shaft, leading to the damage. Dimensional changes, solved that problem.

3) I once wrecked a set of taper roller wheel bearings by failing to adjust for endfloat.

4) The feel of the steering and self centering were improved on one make of car, by adjusting the taper roller bearings in the front wheels to provide 0.002" - 0.004" endfloat.

5) Disliking pounding bearings, I made up an extractor that could be screwed to the drive pulley, and used to thrust on the slackened drawbar, to "break" the 3MT taper in my Mill/Drill. After over 15 years, the bearings still seem to be in good condition. A long time ago, I had to replace the 3/8 BSW thread on the lower end of the drawbar!

I know that taper roller bearings in machine tools are deliberately adjusted to give a preload, but the bearings are selected, by design, and are presumably "oversized" to live in these conditions.

Howard

Look on page 3 of this Nachi publication - brief intro to preload. They seem to be supplied in several levels of preload.

If you look at SKF 7305 angular contact bearings as an example, they supply 3 preloads (GA, GB and GC). They are defined in a table here. For my milling machine X axis I used a pair of the 7305BEGBY version with medium preload, which seems to be a very similar spec to the original Nachi bearings.

There is clearly a whole world of expertise in bearings.

Murray

Edited By Muzzer on 24/08/2017 14:53:34

I have a Wisconsin engine with taper roller main bearings. As I recall, the end of the crank can be clouted with a soft hammer/mallet, but a steel hammer of any description should not be used directly on the crank (they mention using a softer drift, if using a steel hammer). This was not to prevent mushrooming the end of the crank and the instruction was pertinent to bearing life.

Thanks for replies. It was a comment on Alfie Peacock's thread about mounting an MT3 milling collet in the lathe saying that tapping a taper into/out of the taper would be bad for the headstock bearings that turned my mind to this question. I've heard this before, but I wondered if it was one of those things that seem a really bad idea, but actually mightn't be so terrible. I have a problem in that not having an engineering background I've never developed a 'feel' for the sort of forces involved in machining metal or the (obviously superhuman) strengths of machine tools and their components. I'm clearly not alone in that - there's a video on youTube showing a guy trying to stop an industrial lathe from starting by holding on to the chuck key.

From what Hopper said and the discussion on the forum link Oldvelo posted it seems that that there is no real analogy with car wheel bearings - different situation altogether.

As JasonB (who must spend at least 36 hours a day in the workshop!) has been disengaging tooling from his X3 by tapping the drawbar for 11 years without ill effect on the bearings, and Ketan at ARC has said that it hasn't been a problem with the machines he sells despite his initial misgivings, it sounds like whacking (sorry, tapping) out Morse tapers is OK. In moderation at least!

Cheers, Rob

.

Don't be silly. ........... That is far, far too much of an exaggeration.!

It's 33 1/2 maximum as he spends at least 2 hours on the phone listening to my drivel and trying to explain things. Another 15 mins on here and the last 15 eating, poo-ing, drinking tea and deciding to answer the phone or not.

Nick

One thing to bear in mind is that mill spindle bearings are usually opposed taper roller bearings, so when pounding downwards on the draw bar, the force and impact are being absorbed by the top bearing. When atcually using the machine, most of the cutting load is on the bottom bearing. The top bearing is just there to hold the spindle in place, so to speak. So the top bearing could probably sustain a certain amount of minor damage to the races and rollers before it affected the performance of the machine in operation to a great degree. Maybe?