tapered roller bearings | Model Engineer & Workshop Magazine

I’ve spent hours over the last three days looking for tapered roller bearings with tighter than normal tolerances and didn’t find any. Timken and SKF sites list tapered roller bearings with standard and tighter tolerances but I couldn’t find any. So I spoke with their technical support people and was told that, while they list them with tighter tolerances they don’t make them but if someone ordered they might make them. I’ve also searched many bearing distributor sites, in the US, UK and Japan and even sent emails to a few and got replies that they only have standard class K or class 0 tolerances. Does anyone know where to get tapered roller bearings with tighter tolerances?

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Thanks,

henryr

But tolerance and clearance are two different things. You can adjust clearance as you say but tolerance is the machined finish of the races and rollers and the exact size there of.

Sounds like you have to buy the close tolerance bearings from the machine tool supplier who get them made in batches to special order. Hence the hundreds upon hundreds of pounds for Colchester taper roller headstock bearings.

You might try some of the quality Japanese suppliers like Koyo and Naachi. Or the German FAG?

But, depending what you are doing with your little Prazi lathe, the standard grade bearings will probably do the job.

Maybe talk to Ketan at ArcEurotrade. He is pretty up on these small lathes and various bearing upgrades and suppliers.

Edited By Hopper on 10/03/ 05:48:33

Edited By Hopper on 10/03/ 05:49:33

No. I think it was a genuine response to an ongoing debate trying to convey the latest technology to the grumpy old gits of pre-internet days. I doubt that Mr Timken cared too much about the model engineer's lathe market when they were selling wheel bearings to every car manufacturer in the world. It was a different world back then. And I think he was right: roller bearing lathes went on to become the norm and generally speaking seem to perform better than the old plain bearing machines. Compare a roller bearing Boxford or other South Bend Clone with an ML7 and you will soon be a believer. Plain bearings are so .

I recall reading that really fine workers always used solid bearings because rollers caused vibration

Certainly true in the good old days because it's much harder to make roller bearings than plain bearings. Balls and rollers were especially challenging because roller bearings run rough and wear quickly if only one of them is slightly out.

Ball-bearings were popularised by push-bikes because plain bearings exhaust the rider, but early attempts to make them were only moderately successful in that they soon wore and became bumpy. The best early bearings weren't good enough for a lathe – they didn't last long enough before vibration set in.

In the lathe 19th and early 20th centuries many companies tried to find ways to mass-produce high-tolerance rolling parts and failed! During WW2 both the UK and Nazi Germany imported top-end bearings from Sweden because SKF was one of the very few makers in the world capable of producing really good rolling bearings. (Better than anything UK, Germany, Japan, France, Italy or the USA could do, even though all these countries were all in the race, ho ho, geddit.)

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But this was in the long gone world of Trade Secrets, active patents, and semi-understood engineering. 80 years later it's not rocket-science to mass-produce good bearings anywhere in the world. Whilst the best bearings are still premium products, it's because of the extra care, exotic materials, and quality control typical of aerospace and other hi-tech requirements, not because there's any magic in it!

Although plain bearings are the easiest and cheapest way of making a precision smooth running lathe spindle there are disadvantages:

• Essential to keep them well-lubricated. Gravity is good enough for small tools but big ones need pressured oil systems, which cost money to maintain especially if the machine runs continually.
• Plain bearings waste a lot of energy stopping and starting. Doesn't matter in a home or jobbing workshop, but it does in a factory full of big machines restarting around the clock, year after year. While the operator might be completely happy with the machine, the accountant will periodically do the sums to see if it's worth replacing it with something more efficient. This causes consternation on the shop-floor when fine machines are suddenly scrapped despite being good for another 50 years work! Many engineering businesses went bust because the accountant was sent for far too late, or his bad-news advice was ignored.

As always, horses for courses, but today 'good enough' roller bearings are usually the best bet for most purposes, even lathes! Low maintenance, high-reliability, and standardisation means they're relatively cheap and easy to replace. Probably best not to 'save money' by rushing to nastyRubbish.com and buying the cheapest possible bearing you can find on the market though! Very cheap goods are rarely top-quality…

Dave

Edited By SillyOldDuffer on 10/03/ 11:31:51

Remember, tolerance in this discussion is how close fitting the parts will be.

I would expect that the "tolerance" described by the OP is more likely the accuracy of the bearing under operating conditions compared to a "standard" bearing – reduced axial and radial runout that would translate directly to improved part accuracy on a lathe.

Machine tool accuracy bearings were troublsome and expensive to source several years ago. My previous employment was for a CNC machine tool rebuild company & spindle bearings were replaced during a rebuild. Mostly we had specialist bearing factors searching for them & most were NOS. Timken quoted 2 years delivery on one direct enquiry, which led to the original bearings having to be refurbished rather than replaced (crossed roller bearing for a vertical borer). The races were reground and a new set of rollers manufactured. SOD's assertion that " roller bearings run rough and wear quickly if only one of them is slightly out " was not true in this case – a surface finish issue with the finished machine was eventually traced to the remanufactured rollers not being made to the required dimensional accuracy. The table ran smoothly and quietly, and the total axial displacement was within spec. , but the axial error was not in the same place every rotation of the table. Another set of rollers made to a tighter tolerance fixed the problem – suprising the effect of a "roving" 0.04mm error on a machine with a mm diameter table !

On one occasion a precision ball thrust bearing just couldn't be obtained, so BSL (as it was at the time) sent us their entire stock of standard grade bearings & I had to unpack each one, clean it, set it up on a surface plate and measure the axial runout. One ended up being only just outside the specification for the precision grade – we used that & returned the rest. Some of the others were only just within spec for the "normal" grade !

I doubt that a Hobbymat's turning performance would be substantially improved by fitting precision grade bearings over standard grade for a reputable maker.

Nigel B.

A few years back I needed to acquire a number of abec 7 bearings for some spindles that were in the early design stage. Before going too far with the design, which was flexible on size at this stage. I contacted my usual local bearing supplier only to be told that no bearings were available in the particular size I quoted. After ringing round and getting the same answer I contacted SKF themselves, I think they were somewhere like Luton at the time, they were able to tell me that if I placed an order shortly for the forty odd bearings I wanted they would be available as they were going into manufacture in a few weeks. It seems like most things semi specials are produced in batches when a suitable quantity is preordered or likely to be.

Only used taper roller bearings on larger spindle designs for milling or slow revolving shafts. Bearing manufacturers used to produce documents showing bearing configurations for different machine tool spindles, they probably still do. Dependant on spindle size and weight capacity you could probably get away with a set of angular contact bearings and roller bearing.

I made a spindle and thought I could just buy tapered roller bearings. The spindle run out was 0.015 or so mm tir. It turns out that the bearings I bought were just the commercial grade for trailer wheel bearings. It was the concentricity of the inner and taper of the inner ring, as well as the roundness of the taper on the outer ring. At first I thought it was my housing not being true. I bought another bearing from a different batch and that was a lot better, but was 8um of TIR. So instead of messing around and reworking the bearing rings, I just replaced them with spindle grade angular contact bearings. Now it is less than 2um TIR so super happy with it. But the spindle grade are very expensive compared to the regular grade of angular contact bearings. Had I made it to the dimensions that are used in some milling spindles, then I could have got the right roundness and concentricity in a tapered roller bearing. The rollers that I checked were very good for roundness.

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