Quill bearing temperature

Another question I've been meaning to ask here for a bit.

My VMB is now driven by a 3 phase motor and inverter, I can run it up to over 2000 rpm which is nice. It runs very sweetly, but at higher speeds the lower quill bearing gets more than warm, though not too hot to keep my hand on, if it runs for 10 minutes or so. The bearings are sealed I believe so there's no way to re-lubricate them. Should I worry please, or is this par for the course?

Hi John,

I'm sure somebody will say different but I'd be looking to replace them (all).....for me, I would say this is a warning that all's not well..........they may run 10mins this time then 8mins next time.....and so on......

European bearings are never that expensive, it'll be cheaper to change them in the long run.....besides they prob have done a million mile already..........

Just think of the damage that will be done to shafts and or housings if the bearing locks-up......

bin em and sleep easy..........Clogs

2 options, as I see it. As clogs above, or there is some means of preload/axial thrust which has been set too tight - any warming may well exacerbate the preload - and into a downward spiral of too much heat causing more pre-load/thrust.

Most of my machine tool spindles run warm after a period, but 10 minutes is pretty quick to warm up. Can we assume that 2000rpm is above the normal maximum spindle speed? If so it may be that the bearings are grease packed, and running at higher speeds is causing the grease to be churned around, which takes work, which ends up as heat.

Andrew

Two most likely causes would be preload & grease - too much of, too little of or gone hard.

While at the last employment I was able to go on a couple of DTI "Inside UK Enterprise" factory visits, one of which was to Bridgeport in Leicester. Their spindle cartridges were assembled in a clean room, with the grease being precisely pre-weighed into syringes & applied evenly throughout the bearing air spaces. The grease was Klueber Isoflex NBU15 - a soft barium soap grease that costs a small fortune. The assembled spindles were then placed on a PLC controlled running-in rig that ran the spindles gradually up to full speed while monitoring the bearing temperatures - if the temps got too high (over 50 dg C) - the spindles were stopped until cooled to ambient, then run for longer at the speed below which the heating occured before trying to go higher.

We employed a similar - though less high tech - process when assembling greased spindles of rebuilt CNC milling machines & routers. The bearings were lightly greased & lightly pre-loaded, then run in starting at 100 rpm for 1/2 hour before stopping & checking the spindle temperature inside the taper nearest the bearings. When the temperature had stabilised at 100 rpm, the speed was increased to 200 rpm & the process repeated. If the temperature got to 50 C, then let it cool & run longer at the lower speed etc. Running in a high speed spindle usually took at least a couple of days.

In your situation, I would suggest dropping the spindle out, then washing out the bearings in solvent. If the bearings feel OK then dry, lightly grease (NBU15 can be bought in 50 gramme tubes from Ebay of about £25 - otherwise a soft (NBU15 is toothpaste consistency) lithium grease). Too much grease just gets churned around and generates heat ! Difficult to be specific about what "lightly greased" is - some bearing catalogues give an air space volume for the bearing & IIRC the recommendation was about 30% of the volume as grease. If it looks like you haven't got enough grease, then that's probably enough ! I changed the spindle bearings on a Cincinatti Sabre maching centre at my current employment - the bearings were pre-greased with the correct amount of the correct grease & looked like they just had a light, even "shipping" coating, with no obvious accumulations of grease, For preload, adjust to take out the play & then a touch more torque on the locknut. Then run in as above. No temperature measuring device ? 50C is about the most you could hold your hand to - if it gets to that point, stop & let it cool down. As you progress up the speed range, the highest speeds take the longest to settle down.

Quills are particularly picky to set up, as heat transfer out of the bearings through the quill into the head casting is not great. As the running clearance is (should !) be small, expansion can cause the quill to get stiff or seize at higher temperatures.

HTH

Nigel B

I agree with all that Nigel has said. I used to design machines with multiple spindles running at all sorts of speeds up to 8000 rpm. These were lubricated with grease or oil, the higher speeds ran with one shot metered oil systems. If you do change the bearings, go to a bearing supplier and get genuine European manufactured bearings of the correct type. Don't rely on what came out as to what should go back in, find exactly what was put in when the machine was built and duplicate that.

Howard

Nigel,

Given the price of NBU15, I have to ask if you know ...

is Weldtite TF2 'White Lithium Grease' in any way comparable ?

**LINK**

http://www.chainreactioncycles.com/weldtite-tf2-lithium-grease/rp-prod5959

It is very good, but obviously might not be in the same league.

MichaelG.

Well adjusted bearings should run warm, but not so hot you can't keep your hand on them.

The 'counsel of perfection' method for adjusting the preload on roller bearings is to monitor the temperature rise with an infra-red thermometer, and back it off very quickly if it rises too quickly or two high.

Your quill sounds just right.

Neil

All of the advice that Nigel B gives is good information. I rebuild machines for a living, although most are woodworking. We rebuild router spindles that run at anything up to 24000 rpm and they are all "run in" in the same manner as he has detailed. The only couple of points that I would add is:-

a) If you are going down the route of stripping and cleaning /regreasing bearings then please be careful as to how you remove the bearings from their housings and shafts - its very easy to damage them. In fact its so difficult that we would never consider refitting a set of used bearings and would fit new bearings every time (although it's slightly different for the amateur as there is not the financial implications that we have to work with - stripping and rebuilding a router head will cost our customer a minimum of around £2k and there is the cost of lost production as well).

b) If the bearings are sealed type (rs or zz type) it is very difficult to remove and refit seals without damaging them so its not worth trying to open or lubricate them.

c) Lubricating high speed bearings with kluber is a good move because its one of the best lubricants around. However if you go down this route then you need to remove any other oil or grease that's already there (Kluber is not compatible with normal grease sand oils) , we use thinners to clean and wash new bearings to remove any traces of the manufacturers lubricants. You also need to clean out any grease from lubrication ways and grease nipples to stop ordinary grease being pushed into the bearings during servicing etc (the grease points need to be marked so that ordinary grease is not used during subsequent servicing).

d) When using your machine always allow the bearings to warm up before starting cutting. Two or three minutes with the machine idling will allow the lubrication and the bearings to warm and achieve the correct clearances before loading them up with cutting forces.

Martin

Edited By Martin Cargill on 21/12/2016 22:31:40

Well. 5 answers say replace, Neil says don't worry. Just to emphasise they don't get too hot to keep my hand on. Anyway, Maplin are selling infrared thermometers at 20 squids at the moment so I've ordered one and will check the temp rise over a period and see what heppens before replacing. Thanks for the input!

I only counted 3.

The option, to start with first, is reducing the preload, if that is an option in your case and it is more than necessary/prescribed. The same situation would arise with the next set of bearings if the preload is excessive. Sort out the simple possibilities first - it is generally easier, faster and less expensive.

But you should have some idea (as clogs intimated) if this is a new problem or one carried over from before overspeeding your spindle (may have still got hot, given sufficient time, at a lesser speed), or is a developing fault.

Is the temperature rise continuing or terminal at this ten minute interval? If it only occurs when overspeeding, the answer is simple enough. Stop doing it!

How often is speed, in excess of design, really required? I could run my VFDs at x4 (or even x8?) of normal frequency, but I don't. I know it is not safe to do that.

Going into the red area on your car tacho, regularly, is not going to do the engine any favours. Ocasionally for a short period may be OK (or they should have fitted a rev limiter!). A similar analogy, here, I would sggest.

I, for one, did not categorically say 'change the bearings'. That is your choice. Bearings often give some warning of imminent failure. Noise is one, overheating is another, vibration yet another. Lewis Hamilton's engine failure in Malaysia(?) occurred without warning, apparently, and totalled the engine. That was an expensive failure! But they do continually run close to the mechanical limits!

Just FTAOD, the maximum speed on the standard VMB is about 2300 rpm while the varispeed version will run at 3000. So I haven't been actually exceeding designed (?) speed.

FTAOD = for the avoidance of doubt. Just so other people don't waste their time as I had to.

Tony

Thanks Tony, saved me the trouble. I do wish people could avoid these shortcuts.

Doug

So, FTOAD, it has ABA to do with a three phase motor and VFD.

(ABA is an abbreviation for "Absolutely B*gger All".  So much for the context conferred in the OP, then?

* = u

Edited to get rid of the smiley! But not successful.

Edited By not done it yet on 22/12/2016 09:49:46

Edited By not done it yet on 22/12/2016 09:50:41

Edited By not done it yet on 22/12/2016 09:53:12

Edited By not done it yet on 22/12/2016 09:54:26

.

The simplest work-around seems to be; use square brackets instead of parentheses.

MichaelG.

Just done an interesting informal experiment - needed to square up a block of beech as a base for repairing a toy for grandson. Used a 1/2 inch router cutter at max speed which is ~3100 rpm. The bearing did get uncomfortably hot after quite a short time, so maybe things are not well. Once the thermometer gets delivered after the Christmas rush I'll do some more careful experiments and look at either adjusting or replacing the bearings as advised. Will have to fit in around Plan A which is fitting a VFD to the Super 7.

As for the context of my OP, before fitting the VFD rearranging the belts to run at max speed was a real trial, with a 4-step intermediate pulley, supported on a plate bolted down to the top of the column, where you needed to take both belts off and re-fit them in a different order, tighten the quill belt by sliding and clamping the plate, then fit the rear belt and tension that. Also the drive was far from smooth for some reason I never fathomed. So I seldom if ever used the highest speeds and had not noticed the heating issue. The 3ph motor drives the spindle direct through a link belt, I have 4 mechanical speeds plus the variable speed, and everything runs much smoother and quieter. Top speed at 50 Hz is 2160 rpm, I can push that up by 50% by running the VFD at 75 Hz when I absolutely need a high speed. With the VFD I tend to use higher speeds and now notice the heating.

Sorry folks, but FWIW this is an Internet forum so people will use these shortcuts I'm afraid. Saves a lot of typing. You learn a little every day.

Michael - not sure about white lithium grease, as I have not had cause to use it. I found a lower cost, directly interchangeable, substitute for NBU15 from a company called Brit Lube (near Manchester) called "High speed DN Plus) that costs about £40 for a 400 gramme cartridge. We have a Correa CNC milling machine that uses this to lube the gears & bearings in a double angle universal head.

Martin - I had forgotten the miscibility bit. IIRC the old company used gunwash thinners initially, then a blow down to dry (being careful not to let the dry bearings spin with the air), then a wash in some special Klueber cleaner to remove any residues from the gunwash & another blow down. We were somewhat spoiled in that Klueber had (at that time) a depot on the other side of Halifax to the works, so their technical people were easily accessible for advice. We also changed bearings as a matter of course - but easier to do so when someone else is picking up the tab !

Things are quiet at work today & as I have done my pre-shutdown chores (changed back-up batteries & oiled up anything bright), I had a play on an XYZ KRV2000 turret mill to see how that warmed up. The KRV is a Bridgeport clone, R8 spindle & 85mm diameter quill. I put a 16mm end mill in a collet (to stop the drawbar rattling) & fully extended the quill so the head casting wasn't acting as a heatsink. Initial temperature (measured with an un-calibrated non-contact IR thermometer) at the bottom of the quill just above the end cap was 12C, with the workshop ambient temperature around 15C. Spindle started at 3000 rpm (max 4200 - 3000 is the start of the "red line" area, suggesting maximum continuous revs).

After 5 minutes - 15C. 10 minutes - 16C . 15 minutes - 16.5C. 20 minutes 17.3C. 25 minutes 17.9C. 35 minutes (got talking & missed 30 minutes !) 19.7C. I stopped at that point & the quill felt (in local vernacular) "aired" to the touch i.e. the chill had been taken off, but not warm by any means.

This machine runs quietly - at 3000 rpm there was slight noise from the gearbox, but I had to get within a metre of the machine to hear it was running above normal background noise. It also cuts well & leaves a very good finish, so I think the spindle bearings are nicely set up. Hopefully this could be used a sort of benchmark ?

To kill the accursed "smiley" - try leaving a space or two before the closing round bracket.

Nigel B

Nigel, that's very useful information, thanks. My quill was definitely getting more than "aired"!

.

Thanks, Nigel ... It was just a seasonal [Scrooge-like] thought.

I use the Weldtite [an inappropriate name if ever there was] TF2 on slow-moving parts like focussing mechanisms; because it gives them the right 'feel' ... but I have no idea of its high-speed characteristics.

MichaelG.