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.

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

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.

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

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!

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

Tony

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

(ABA is an abbreviation for "Absolutely B*gger All&quot.  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

As the most likely result of overheated bearings is worn bearings that need replacing, and perhaps the risk of starting to get a poor finish (I think you would need a MUCH more alarming temperature rise to risk then seizing suddenly) perhaps the answer is just top keep half an eye on the machine making sure it continues to operate smoothly?

Really we could do with Ketan's view on this – he is 'Mr Bearings'.

Neil