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Appropriate grease for milling Spindle

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Joseph Noci 118/06/2021 21:21:17
1030 forum posts
1272 photos

I have a Milling head that comprises two taper roller bearings - ID 1.8inch / OD 3.5inch. The spindle was last re-packed with grease some 17 years ago by its then owner. I have used the mill expensively since then and it has behaved well.

Of late it sounds a little noisy, so I stripped the spindle down, and found the grease needs replacing. I have cleaned all and the bearings still look good. Problem is what grease should I use? The head is an old British make, no handbook or manuals, and the previous owner is no more...

The spindle has often worked at speeds up to 3000rpm with mild heating.

I have looked at similar spindles and the grease they seem to use, but most are esoteric and available only in first world places...

Common to me is Castrol greases, but limited varieties - NLGI-2 seems is what is needed, which I can obtains, but BNS - a bentonite clay based grease, an MS grease - a lithium soap grease with Molybdenum Disulphide and and LM grease - a general purpose Lithium soap grease...I suspect these are all typical automotive type greases - for wheel bearings, and bonnet hinges..

Any ideas?

Joe

Nicholas Wheeler 118/06/2021 21:36:02
823 forum posts
59 photos

I'd use the LM grease as for wheel bearings. I have some that's in a metal tin priced in shillings that Dad bought for his Bantam...

HOWARDT18/06/2021 22:05:00
837 forum posts
39 photos

Kluber NBU15, if you can afford it. Seriously what ever you decide to use ensure you keep to the recommended amount according to the bearing type and size. Too much can be as bad as not enough.

Graham Stoppani19/06/2021 08:26:34
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109 forum posts
21 photos

When I bought my round column milling machine I found that the top of the two taper bearings was running bone dry and the lower bearing was nicely lubricated with the grease that had melted and dripped down from the top bearing! So I would recommend a grease that has a higher melting point. I'm currently using a Castrol LM grease and haven't seen any evidence of it melting so far.

Dave Halford19/06/2021 09:35:24
1891 forum posts
22 photos

BNS or LM which ever you can get in sensible amounts. Like Nick I have some ancient 50 year old tins that are still good.

Joseph Noci 119/06/2021 10:18:18
1030 forum posts
1272 photos

Thank you.

Both BNS and LM are very common here, in 500gram tubs. It seems very difficult to find definitive usage specifications for these greases though - the Castrol datasheet is so sparse its not worth the two sheets of Epaper its printed on!

The BNS grease has Bentonite in it, which raises it operating temp, but they indicate nothing wrt bearing speeds, etc. All these data sheets refer to wheel bearing use, which is very low speed..Ditto the LM greases.

All the 'Pro' greases relate performance to the bearing DN ratio , or Ndm ratio, normalising bearing speeds, but these Castrol greases glaringly omit any such info.

Maybe I should cease my pedantism and stuff the grease in and get on with it!

Thanks Chaps!

Joe

Kiwi Bloke19/06/2021 10:34:54
625 forum posts
1 photos

I had hoped that someone would by now have provided authoritative information that would let us all understand more about the myriad grease types and specifications. I'm little wiser after grinding through no end of data sheets, over the years. One thing seems widely accepted : don't use greases loaded with moybdenum disulphide in ball or roller bearings. Water-resisting greases tend to be calcium soap types.

As I understand it, the NLGI classification refers to the 'thickness' of the grease, but I don't think it tells you anything about how the grease behaves as it warms up. NLGI-2 greases seem to be good multi-purpose (for our purposes) greases. My memory of Castrol LM grease, half a century ago, was of an almost transparent, soft, lithium soap grease, described as low melting-point, usually with a little separated-out oil on its surface, in the tin. (Memory could be faulty, of course...) Now it seems to contain opaque fillers (bentonite?), is much stiffer, is called a high melting-point grease, and doesn't separate out as readily. It's still commonly used in wheel bearings, etc. Same name, different stuff. Confusing.

Will a friendly tribologist help us, please?

Edited By Kiwi Bloke on 19/06/2021 10:38:46

old mart19/06/2021 18:59:28
3524 forum posts
217 photos

LM is what I use, and avoid overpacking. At least 50% airspace should be left when assembling.

Nigel Graham 220/06/2021 00:20:53
1898 forum posts
26 photos

A valuable discussion.

Kiwi Bloke -

I accept your advice that it is widely accepted that Molybdenum Disulphide greases are unsuitable for ball and roller bearings, but that information is new to me! Could you explain why they are, though, please?

Kiwi Bloke20/06/2021 02:22:39
625 forum posts
1 photos

Hi Nigel, good question! We live in a world where any idea has the potential to become popularly-held, and popular is often mistaken for authoritative. The 'no moly in rolling bearings' idea is much repeated in fora. As you know, lack of knowledge is no impediment to the dissemination of viewpoints, especially in fora inhabited by people without relevant specialist knowledge. I make no claim to specialist knowledge about lubrication of bearings, but I have at least dug around in manufacturers' literature, to try to get to the bottom of this.

As far as I can tell, in spite of warnings to the contrary, moly-containing greases get used widely in, for example automotive wheel bearings, with no apparent problem. However, these greases may contain only 5% solids. It is probably when the solids content gets above this that problems may occur. Two possible mechanisms are suggested. The balls or rollers may skid, causing micro-flat spots. The solids may clump into particles large and hard enough to indent the balls, rollers and/or tracks. Unfortunately, the manufacturers don't really talk about this, perhaps because of liability concerns - or, perhaps, because it's a non-problem.

It does seem to be accepted by the manufacturers that solids-containing greases (including those thickened with clays like bentonite) may cause bearings to run noisily, so I guess one has to be careful about solids. Noisy running doesn't necessarily mean damage, apparently. My impression is that, in easily-available 'multi-purpose' greases, solid thickeners are commoner than they used to be.

So, is the moly worry an old wives' tale, or popular dogma? I don't know for sure. Perhaps for our precision spindles, etc., we should play safe and use soap-thickened greases, rather than ones thickened with clay or other solids.

RMA20/06/2021 08:59:40
302 forum posts
4 photos

Ordinary LM grease is quite adequate for the purpose. If there's no seal in the assembly, it would be prudent to check more regularly than 17 years if the machine is used regularly and speed is a concern if you run for long periods.

The amount of grease is very important to bearing life. Pack the cone fully to ensure grease is where it's needed, particularly at the thrust end of the rollers. The easy way to do this is by putting a quantity of grease in the palm of your hand and rolling the cone through it until all the voids are full.

Nicholas Farr20/06/2021 09:54:28
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3154 forum posts
1435 photos

Hi, it is always best to use the lubrication type specified by the machine manufacturer, wherever possible. Lubrication is a fairly involved science and many factors play their part including; type of bearing, speed, operating temperature, temperature dissipation, load, shock load, vibration and frequency of use to name some of the important things to consider. SKF Lubrication may give you a bit of insight on the many considerations of what type of grease to use.

Regards Nick

RMA20/06/2021 10:31:39
302 forum posts
4 photos

I agree, always best to follow the manufacturers recommendations but in this case the OP doesn't have a manual. He does say it's an old British make but doesn't give the maker of the bearings. If they are Timken, my advice is as I mentioned above. I served my time there and spent a while as a tech rep for them. We advised all manufacturers/customers as to lubrication matters depending on the application.

Lots of fancy products have emerged over the years but sometimes you just can't beat the basics. Regular servicing is paramount to anything of course.

Joseph Noci 120/06/2021 14:14:31
1030 forum posts
1272 photos
Posted by Nicholas Farr on 20/06/2021 09:54:28:

Hi, it is always best to use the lubrication type specified by the machine manufacturer, wherever possible. Lubrication is a fairly involved science and many factors play their part including; type of bearing, speed, operating temperature, temperature dissipation, load, shock load, vibration and frequency of use to name some of the important things to consider. SKF Lubrication may give you a bit of insight on the many considerations of what type of grease to use.

Regards Nick

Well, I tried that site - read through each of the 8 sections. All I discovered is that you need to be a rocket scientist to understand any of that!

Those that suggested a LM NLGI2 grease have it - I have just packed the bearings and re-fitted them. The bearing showed no signs of heating at all - they just looked ok..so after 17 years with the same grease in them - they did fine!

Joe

Nicholas Farr20/06/2021 15:44:44
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3154 forum posts
1435 photos

Hi Joseph, well I did say it is involved, but thankfully, in my maintenance years, I didn't have to worry about it, just used what the tech sheets for each plant said in the book that the tech guys produced. Myself, like you and others had suggested, would use the LM grease, as I don't think these machines come into a high speed bracket.

Regards Nick.

Nigel Graham 220/06/2021 23:50:16
1898 forum posts
26 photos

Kiwi Bloke -

I suppose the clue is in that "widely accepted"...

Anyway you set me off on a little simple research.

I have a nearly-empty tube of Dow-Corning 'Molykote 44' - a silicone grease with Molybdenum-diSulphide (MDS) additive. The nearly-worn away printing seems to mention light-duty bearings.

My new tin of Molyslip 'MLG EP' (extreme pressure) grease, carrries small print revealing it contains MDS and Lithium, and is suitable for ball and roller bearings.

I had bought some lubricants from a military-surplus stockist, including 'Grease XG 274'. My admittedly out of date copy of the "Blue Book" - an MoD directory of NATO-stock fuels and lubricants - showed it is a general-purpose compound suitable for race-type bearings. That contains no MDS but careful browsing of the book showed a few other oils and greases that do, and used for bearings. Indeed, it includes Molykote 44, for radar bearings, it says, [and steam-oil for saturated-steam, was used for oiling torpedo-tube mechanisms!] T'net shows this MDS-holding grease is sold for bearings.

'

So where does the "widely accepted" wisdom come from? As the 'Blue Book' shows, and as we ought expect, no lubricant is right for all applications and conditions. Some oils and greases are universal enough for our relatively modest uses; others are designed for very particular purposes. Some will mix with others, some will not; and so on.

I reckon someone somewhere misinterpreted a specific ban on MSD-greases (or a particular type) for lubricating ball and roller bearings in some specific situation, as general for the compound; and went and spread the incorrect message far and wide.

Kiwi Bloke21/06/2021 02:41:13
625 forum posts
1 photos

Posted by Nigel Graham 2 on 20/06/2021 23:50:16:

Kiwi Bloke -

I suppose the clue is in that "widely accepted"...

Yes, agreed, I think I should have said 'widely held opinion...'

Whereas it seems to be a challenge to select optimum lubrication for a particular bearing application, I think that in our workshops one can't go far wrong by using a lithium-soap-thickened NLGI-2 grease in rolling bearings. Cheap and easily obtainable, too.

The bearing manufacturers say 'consult the lubricant manufacturers', and the lubricant manufacturers say 'consult the bearing manufacturers'. Since the choice of optimum lubricant appears to depend on so many things, it's not surprising...

gerry madden21/06/2021 12:15:21
228 forum posts
119 photos

The fundamental problem is that lubricants and bearings are two of the most highly marketed engineering products you can get, which results in reams of apparently confusing / complex / contradictory information which proliferates undue quantities of folklore and old wives tales. The fact is the minutiae are generally only applicable in the cases where you want to push products to the limits of their performance, for example trying to get that last 5% of life or 2 degs lower running temperature at max speed and high loads in some predetermined product test cycle, or 1 anderon less in noise.

There is really nothing I come into contact with in my 'hobbying' where I get anywhere near having to meet industrial performance standards and I suspect the same is true for many others on here.

So, as a life long bearings engineer, I can recomment not getting too hung up on things like what grease to use in you spindle bearings or other popular devices. If the manufacturer says use 'LM' and you only have a tin of Dow Corning Molykote LT2 containing 'moly' use this instead. It may not be the "technical best" but it will do your spindle no measurable - on a hobby workshop basis - harm, and will probably still outlast you !

Of course there are some exceptions to this general guidance, but not too many.

Gerry

Nigel Graham 221/06/2021 14:10:03
1898 forum posts
26 photos

The question of lubicating milling-machine bearing is particulalry slaien tpo me because my Myford  VMC mill spindle and quill need attention but there is no obvious way at all, even with the diagram available, to dismantle and service it safely.

However, something of a digression credited to Gerry...

An " anderon " ?

I appreciate that's what your company presumably used internally at least, but is it a recognised unit or a local-convenience one, like calling a potential-difference so-many AVOs?

Puzzled, I looked it up!

It seems to me either coined by the inventor of the particular test or the manufacturer of the test-instrument, of the name Anderon; or become a local-name given by its users, rather as we might loosely refer to "Stillsons" rather than "pipe-grips" : the maker's rather than generic name.

'

The recognised unit of sound pressure level in air, is the dB, the decibel, not on its own because that would be meaningless but " re[ferred to] 20µPa " .

So 0dB re 20µPa is equivalent to 20µPa. (from log to base-10 [20/20] = 0).

It was chosen because it is the incredibly tiny minimum pressure detectable by a fully healthy human ear, and =

5 X 10^(- 9) Bar,

if my arithmetic is correct. Puts the Bar*litre in its place and says something for the whispered sweet nothings!

The scale is fully logarithmic but the results for environmental health and medical purposes are sometimes weighted, indicated by the letter A, to compensate for Nature not giving our ears fully-linear frequency responses over their mean 20hz - 20kHz bandwidth.

In water, for marine sonar and biology, the reference 0dB level is a mere 1µPa; 1 X 10^(-11) Bar

.

The Anderon meter measures vibrations in bearings, vibrations in steel that become vibrations called sound in air, and if I recall properly though it wasn't my field, vibrations in solids are measured in dB re a fraction of g (gravity, as the sensor is an accelerometer).

So whilst the machine no doubt give you a very accurate diagnosis of the bearing's condition  and presumably, directly or indirectly, the sound pressure level at the conventional 1 metre from it, I would be very surprised if the name is no more a standard unit than AVO for volts. If the results are given to customers, nowadays at least they would expect standard units.

My work used sound and vibration instruments, mainly but not only from one of their leading manufacturers, Bruel & Kjaer (Danish but now foreign-owned). They only ever used SI units, not things called "BK", in their advertising and instruction manuals!

 

Edited By Nigel Graham 2 on 21/06/2021 14:16:31

gerry madden21/06/2021 15:16:04
228 forum posts
119 photos

Hi Nigel,... its been 20 years since I was in the inspection field but 'anderons' are indeed structural vibrational acceleration values. These are then modified mathematically for the speed and the size (i think) of the bearing under test. The overall signal signal was then split into 3 frequency bands, with each band being applicable to the signatures typically produced by different components of the bearing. An inner ring defect would give high vibration in the low band. Grease on the other hand can cause vibration due to the crystaline additives and other hard particle contaminants that gets into grease during manufacture. The 'crackling' sounds that emanate from grease would tend to appear in the high band.

These anderon frequency bands enabled one to track down production issues more easily.

Gerry

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