Servicing Machinery Bearings Properly

Some of the online bearing removal/installation articles and videos that I have reviewed make me cringe. Although all bearing work should be carefully planned and carried out, bearing work on precision machinery requires extra care in order to preserve the accuracy of the machine and extend its serviceable life. Several manufacturers have posted standards and techniques on the subject. This site is a good example:

http://www.nsk.com/services/maintenancerepairs/properhandling.html

Bill, there are some pretty horrible videos on Youtube about rebuilding lathe chucks too -- using hammer on the chuck key and screwdrivers to get them apart instead of using the jacking bolts! So misinformation is not uncommon.

Good bearing guide you linked to there.

One thing I did not notice there was mention not to over-grease bearings. Always leave 30 to 50 per cent "air space" in the bearing or bearing block otherwise it will overheat, cook the grease and wear prematurely. Saw this happen time and time again in industry. Probably one of the most common causes of premature failure on large air-con plant blowers and the like.

I should think the same principals would apply on miniature bearings. In fact, if you open up brand new sealed bearings you will see the manufacturers use the barest skerrick of grease, less than 50 per cent full by far.

There are a lot of people out there who have a very poor understanding of how to treat bearings. Even "skilled" fitters, mechanics etc. often have no real idea of the principles behind the modern ball or roller bearing and even less when it comes to some of the older type technology such as plain or white metal bearings even wood is used in some circumstances. As the works engineer in a large factory I am in charge of the maintenance and installation of a large number of different types and sizes of machines and one of my first tasks with any new maintenance apprentice or employee who we take on is to educate them into the mysteries of bearing removal, fitting, and maintenance.

I have fitted many thousands of bearings over my lifetime of every description (yes even wood ones) and my major findings are this:

Never ever let a hard hammer anywhere near a bearing. This includes using them on assorted drifts, bits of pipe etc.

When ever possible always use either a purpose designed press or some arrangement of screw, spacer, push or pull device to fit bearings.

When removing bearings the above advice is the same unless you are intending to scrap the old bearing.

When fitting medium to large bearings it is a good idea to GENTLY heat the bearing first to fit it to a shaft. Never use naked flame always use either an induction heater or even a hotplate but remember we are talking 100 or so degrees Celsius not cherry red heat!!!

Never fit a bearing to a shaft by pressing on the outer ring or fit into a recess using the inner ring.

As Hopper advised do not over fill a bearing with grease. I always show new starters a brand new bearing to demonstrate this point.

The maximum speed for a bearing is attained when running in oil if this is the design of the machine carefully remove any manufactures grease before fitting using a suitable solvent.

Never ever dry or "clean" a bearing using compressed air !!!!

When fitting new bearings cover the work surfaces with a plastic sheet and do not remove the packaging until ready to fit the bearing . Cleanliness is vital.

If you follow the above instructions then you ought to get a long trouble free life from your bearings. Remember that over 95% of bearing failures can be traced to fitting or contamination problems.

I agree with everything that Max has said.

I would just add that if a bearing has had its lubricant removed by solvent washing never spin it dry in your fingers to see if it rotates smoothly. If you must spin it always lubricate it with a little light oil first.

Eric

Fantastic Responses!! Professional wisdom based on years of experience is worth its weight in gold. I have learned a great as a result of posting this as well as other bearing related threads. I am replacing the spindle bearings in my Myford Speed 10. Based on what I have learned not only from ME folks but also from various manufacturer online technical data, I will be taking much greater care with the new bearings during the reassembly. In my professional career as a safety officer, I conducted many training courses. One of the issues that I stressed to subordinate safety officers and tradesmen was the important difference between training people and educating people. When we train people, we tell them and show them WHAT to do. When we educate people we tell tehm WHY they need to do it that way. This provides them with knowledge of what could happen to the work or the person if they deviate from the prescribed standards.

THANK YOU. I HAVE BEEN EDUCATED.

In fact, if you open up brand new sealed bearings you will see the manufacturers use the barest skerrick of grease, less than 50 per cent full by far.

There is a reason for this, and it is not to extend the life of the bearing!!! I have fitted many thousands of bearings in automotive , electrical and mechanical equipment. I have always packed the bearing full, rotated it by hand, and then removed any excess. I only began to notice premature failures of bearings when the "sealed for life" junk came out. not putting enough grease in a bearing is a sure fire way of increasing sales. If I cannot get an unsealed bearing, I pop out one of the seals ( they are not actually dust tight anyway, most are all metal) and repack the bearing FULL. after all, a bearing with a grease nipple (Zerk to our overseas cousins) will be greased until grease is seen issuing from the relief hole, or the seal, and this means the bearing, and the surrounding casing is absolutely full. When I started my apprenticeship in 1967 one of the first jobs I had to do was recondition a huge pile of electric motors which had been removed from an old powdered milk plant. They were all between 2 and about 10hp and had been in continuous use since 1937 when the plant was built. They were greased daily, and the air vents and windings blown out weekly. They were stripped, washed out, bearings repacked, and put back into service. very few if any of the bearings needed replacing. Granted they were all Brooks of Huddersfield cast iron framed industrial motors, but they had seen 30 years virtually continuous use! I have seen bearings fail with over greasing with a grease gun, because the grease finds its way into the inside of the machine, where it tracks dust back into the bearings, but this is rare. There is no surer way of making a bearing fail than not putting enough grease in it.

Roller bearings need little lubrication purely because there is virtually no rubbing friction, so half full is more than plenty.

For taper roller bearings the oil or grease is mainly there to lubricate the roller ends and for ball bearings it's there to lubricate the cage.

Martin..

I have recently been on an SKF bearing maintenance course as part of my apprenticeship and we were told that bearings should be completely filled with grease and housings should be about 30% filled. We always use bearing installation tool (basically a plastic drift) in the workshop when we're installing bearings.

It's worth mentioning that it does depend on the job. Overpacking does little harm at low circumferential speeds but can be catastrophic at high speeds due to the grease churning and overheating. Truly high speed spindles have circulated oil or oil mist systems, sometimes using the pumping effect of the taper bearings themselves. In reality, the speeds and sizes commonly seen don't need such measures.

From Page 161 of the Timken Industrial Bearing Maintenance Manual

http://www.timken.com/en-us/products/Documents/Industrial-Bearing-Maintenance-Manual.pdf

“Grease should be added any time the amount in the bearing falls below the desired amount. The grease should be replaced when its lubrication properties have been reduced through contamination, high temperature, water, oxidation or any other factors. For additional information on appropriate regreasing cycles, consult with the equipment manufacturer or your Timken representative. It is important to use the proper amount of grease in the application. In typical industrial applications, the voids in a roller bearing should be filled from one-third to two-thirds with grease. Less grease will result in the bearing being starved for lubrication. More grease may create churning which generates additional heat.”

The (e.g. Timken) manual is well worth a review especially the section on lubrication and lubricants. Most of the information is generic. I am a firm believer in following the manufacturer’s instructions for any machine or device. Industries consider the machine design, materials and components when they compose the instruction manual in terms that can be easily understood by the majority of prospective users. Some machines, such as my Myford Speed 10, pre-date present-day lubricant technology by many years (my Atlas 618 lathe is over 50 years old). It is therefore prudent for me to assess both the lubricant’s technical data and the bearing's technical data in relation to the machine manual and the functions that the machine will be called upon to perform. A little additional advice from ME certainly helps me decide the best course of action.

Cheers to all

Hooray. It’s Friday evening - Fish ‘n Chips night at my house

When I was a young feller, Friday night was pay night, fish ‘n chip night, and fun-with-the-wife night.

Now that I am much older and retired, all I get is the fish ’n chips.

Hi, below is an extract from a SKF bearing maintenance handbook.

Bearings in general should be copletely filled with grease, but space must be left in the housing for any grease that the bearing does not need onece it is first started.

On the subject of fitting bearings, the first thing is cleanliness, and then the fits and tolerances followed by the right method and the correct tools. The methods and tools depend largely on the type and size of the bearings and thier applications. However sometimes where you have to replace a rolling element bearing in non ideal conditions and when production rules, unorthodox methods may have to be used for mounting the bearing onto a shaft and into its housing and the correct tools cannot be used, therefore you may well have to use a drift. If you do use a drift it should be used cautiously and never be made of brass, because contary to belief that it would be less damaging is a myth. Using a brass drift on a hardend bearing will chip fragments of brass (which can be as tiny as a shiver in your finger) off, which will end up in the bearing eliments and will cause premature failure of the bearing. If you do have to use a drift it should be of mild steel as this will just mushroom.

Regards Nick.

Bearings in general should be copletely filled with grease, but space must be left in the housing for any grease that the bearing does not need onece it is first started.

Not the case with machine tool spindle bearings, though. It is usual to fill 20-30% of the airspace within the bearing, as excessive grease leads to overheating. I visited the Bridgeport works in Leicester some years ago & their spindles were assembled in a clean room, with the grease pre-weighed in syringes that were used to evenly fill the spaces between the balls. The completed spindle assemblies were then run-in on a special test rig that built up speed gradually while monitoring bearing temperature - if it got too warm the spindle was stopped, allowed to cool then run again at a lower speed for a while before the speed was increased again.

At my last employment (machine tool rebuild & retrofit company) we worked in a similar way, though the grease insertion was not as precise as Bridgeports. We used Klueber grease (not all greases are equal !) & followed Klueber's recommended running in proceedure, keeping a temperature log to monitor running in. Starting by running at a low speed for 15 minutes, the speed was increased in stages for 15 minutes at a time & the temperture monitored (measured as close as possible to the bearings - usually up the spindle taper). The temperature was not allowed to exceed 50 degrees C - it it got close to that, the spindle was stopped, allowed to cool completely & then the running in started again at the speed below which the temperature had increase. The running-in procedure could take two or three days to complete on high speed (12,000 rpm) spindles, but if too much grease was used then the running-in period was either excessively long or it was not possible to complete it at all - then the only recourse was to strip the unit, clean out the bearings & re-grease more sparingly.

I recenlty replaced the spindle bearings on a Cincinnati Sabre machining centre at my current employment - a "matched set" of 3 RHP precision angular contact bearings that came pre-greased. The grease applied was a single line about 2mm diameter that looked like it had been applied with a syringe to one side of the balls only. Running-in after the bearing change took about a day and a half to get to the 9000 rpm maximum without generating excessive heat.

Regards,

Nigel B.

Phil Whitley, well said !

This is very interesting. I have always assumed that you plaster a new bearing with grease, but that the excess is rapidly squeezed out into the surrounding void. I suppose this isn't too bad an approach having read the above comments and the SKF guide - as long as the excess really has somewhere to go.

Neil

Buy the best you can. Not cheap Chinese copies.

I have a Maximat-Compact, 1966 era. As I understand, the Austrian manufacturers were attempting to compete with/copy? the MyFord and they do bear some similarities to a MyFord. The spindle bearings are SKF tapered roller bearings. Each bearing has a grease nipple, aka Zerk fitting and the instructions say to grease every 500 hours.

Since it is not a good idea to fill the bearing/housing with grease, how would one know that the bearing/housing was 40-50% full? From correspondence with other Maximat owners, who in earlier years were able to correspond with the factory or the factory's representatives, I learned that the factory assemblers would slowly fill the bearing until grease oozed out from the rubber seal. The new owner was told that grease would come out from the seal and that the new owner should not run the spindle at higher speeds until this stopped occurring. Another tip was to feel the spindle housing and if you could not comfortably keep you fingers there, the speed should be reduced or the lathe stopped and allowed to cool.

Any thoughts or advice?

Paul

There is a big difference between different applications of rolling bearings. Consider a hobby lathe spindle and the wheel bearings on a car. Get your lathe a bit too hot and it might make a bit of a mess. Get your wheel bearings too hot and the excess grease will go into the brake drums or disc pads. And then bearing failure is not your major concern.

it is alwa\ys important to look at all the circumstances, not to apply general advice as though it always applies.

cheers, tim