Preload on Roller Bearings - Tom Senior Mill

[districtgrandmaste]

I bought a Tom Senior Model E Mill three years ago. I find it excellent but now extremely noisey - specially at top speed - and I run it fast often when drilling.

This noise is undoubtedly due to the roller bearings in the quill being - shall we say - worn. The quill is now in pieces and new bearings are being fitted. I've handed the job over to my local machine shop and they say - do I know how much 'preload' is recommended.

Has anybody any technical information please? I'm out of my depth!

[Noddy]

Now now John,
"a good Chinese one" may be, but what if it needs a rebuild BEFORE you use it?

Keith

[mutley]

"a good chinese one" that may be a contradiction in terms.

Andy

[alanstepney]

The bearing manufacturers should be able to tell you what preload to use.

Assuming that they came from one of the major UK bearing stockists, they are probably Timken or one of the Japanese makes. All of the reputable makes are interchangeable, so contact Timken (with the part numbers or bearing type + size) and see what they suggest.

[mutley]

I did. I got a chinese bench drill and if you push to hard the column and table bends, net result is a drunken hole. I now do all accurate drilling in the Tawinese mill and only light work in the drill press.

Andy

[Noddy]

I've any amount of Chinese stuff, e.g. Nikon DSLR and lenses, also little brother is off to visit his future in-laws in Northern China later this month (-20 to -30 celsius, ouch!).

It is just that, labour and environmental costs aside, you get pretty much what you pay for.

Japan and now Taiwan both produce machine tools as good as any, but we don't see them now, because the niche for those products is pretty full of the remaining European or US makes.

China is shipping products to a price and is doing it well.

It is probably one of those 80%:20% things; you get 80% of perfection in 20% of the time. Getting that other 20% of fit and refinement would probably raise their costs five fold (I'm sure the Chinese are capable of it (out of 1.5 billion, they are sure to have some analy retentive types), it's just not worth their while at this time).

For the Rt W Bro, Replacing the bearing will hopefully have his little machine producing accurate work quietly again for longer than we're around.

PS with Chinese diggers, there's a good reason why most get sold brand new at auction - no warranty !

Keith

[districtgrandmaste]

Thanks Alanstepney for your very sensible suggestion - I will follow it up.

I would prefer HELP when I make a posting and not find it hi-jacked to persue various agendas!

[ianengr]

I have been down this track with my Chinese Turret Mill about 4 years back, and found that the Bearing suppliers/agents would not give me any sort of indication of pre-load value.

From what I was told, they abdicate all responsibility of this to the machine manufacturer or repairer because there are so many variables in aspects of design and manufacture requiring great care and precision, of which they have no control over.

I would have to say when looking at the working attitudes of many of those who care to call themselves "tradesmen" I would do exactly the same.

In my case the pre load for the angular contact bearings was determined by the difference in size of the tubular spacers between the inner and outer races of both bearings. when fully tightened, the retaining nut on the spindle compresses the inner spacer, the amount of pre load can then be felt on the outer spacer, this can be increased or decreased by removing very small amounts from the ends of the inner or outer spacer respectively on a Surface Grinder. I was able to slide the outer spacer easily by hand when loaded, which I doubt would have exceeded 30 - 40 Kg. the 80 x 50 mm. bearings had load ratings well into the hundreds of Kg. from memory. This assy was an easy but very close sliding fit in the Quill with a retaining ring / seal housing on the bottom which clamped the outer races and spacer against a shoulder in the bore of the Quill. There was nothing wrong with the original bearings except they were 80 x 35 mm., the parallel bore of an R8 spindle is a little over 25 mm. leaving a wall thickness of only 5 mm through both lower bearings the rigidity was as one would expect...
I was able to locate 80 x 50 mm. bearings and then replaced the lower half of the spindle, the top half with driving splines being pressed in.



Regards,

Ian.

[alanstepney]

DGM. try wading your way through this lot.!
Lots of information there.
www.google.co.uk/search?hl=en&q=bearing+pre-load+&btnG=Google+Search&meta=cr%3DcountryUK|countryGB
(You will need to copy and paste that lot I reckon.)

Engineers Emporium did have the manual for the, or one of the, Senior mills, for sale.
Dont know if it had the information you want in it, but perhaps worth asking them, or even b-b-b-b-b-uying it. (Sorry about the bad language! lol)

[Noddy]

Another possibility is to google machine tool re builders, and ask around them.

Is the nut for pre-load easily accessible? (I'm not familliar with the E type head).

If it is, and failing everything else, your two boundary conditions are:

Lower boundary: excessive end float causes chatter

Upper boundary: most likely, bearing runs warm, and as there will be significant conduction losses, the contacts of the bearings in the races will be hot by the time the outside feels warm!

If all else fails, then I would set a reasonably heavy cut on a piece of scrap and tighten the adjusting nut a little at a time (by finger or finger and rag pressure at first), until any chatter disappears.

perhaps some of the members with more experience than me would like to comment on this.

Keith

[alanstepney]

The "quick and dirty" method is to tighten the nut until the bearing starts to bind, or run it and see if it runs hot, then slacken off one flat of the nut.

[circlip]

Oh dear hindsight is a great teacher, perhaps districtgrandmaste should smack the hands of whoever stripped the head for bitsing something they obviously knew nothing about. If memory serves me right, I think I read somewhere that pre-loads are set by fixing a bar at right angles to the spindle and checking the pull with a spring balance a certain distance away from the spindle centre whilst tightening the clamping nut. Bearing manufacturers may be able to help, but I wouldn't be surprised if Uncle Tom's assemblers didn't have their own "little black book" on the subject. I say this having worked in engineering in the locale of their plant. Flat cap and oily rag engineering, "Leave it there lad, we'll sort it art for thi"
Noddy highlighted it for you, machine tool rebuilder.

[steam4ian]

G'day all

I don't know Tom Senior from the legendary Jack Schitt; BUT I do think Alan is right regarding bearing preload, it is after all how wheel bearings are set up. It is important that both bearings remain loaded under all normal conditions and this will depend on the cutting thrust. If the main thrust is in the axis of the shaft then the preload needs to be higher.

Regards,
Ian

[districtgrandmaste]

Thanks for the helpful contributions. I've had new bearings installed, enjoyed myself making a couple of wrenches to tighten things up and now know how to take apart and put it all together.

It runs much quieter now and I shall keep the helpful comments in mind!

Was it me that caused DrJ to disappear? - if so I apologise unreservedly!

[Noddy]

Hi DGM,

Please to here that you got it sorted.

any chance of a quick writeup with a few photos for future info?

regards
Keith

[abby]

Districtgrandmaster - what are the torque settings ? handy for us all to know , and don't worry about Drjohn as I am sure several members have taken offence at his rude and often ill-informed style of communication , the fact that he has removed his posts says it all , pity I wanted to know more about drawn cast iron bar !

[districtgrandmaste]

Hi Abby - thanks for the interest but my wrenches are nothing clever and I don't do photos I'm afraid!

What I did was to tighten up the 'Bearing End Cap' - that's a screwed fitting at the bottom of the quill and then tightened down the 'Bearing Locknut' at the top of the assembly until there was no shake in the quill and then tightened the crossscrew of the locknut. Then I screwed down the 'Bearing Adjusting Screw' until it bottomed on the outer ring of the bearing - that was where the wrench was really worthwhile!

The quill is now reassembled and running nicely but I'm wondering how long for! Still I'm prepared to remove and adjust further if there's any 'chatter' apparent after a while.

Having taken the quill apart I can see many people have been there before - some with cruelity to metal!

[circlip]

Bringing this chestnut back districtgrandmaste, you probably already own it ,but on the following link there is an instruction book for the Tom Senior mill with reference to the bearings.
www.colinusher.info/index.html