Using Needle Bearings

[SteveW]

Yesterday I met someone advocating using needle bearings in place of ALL plain bearings on the grounds of cost, ease of use and life expectancy. The target application ranging from wheels through to crosshead and everywhere in between.

He showed me a catalogue for needle races down to 1/8" shaft. He used ER forty something material for the mating shaft and had this nitrided.

The only significant rule of thumb was to use caged needles for rotating and un-caged for reciprical applications.

What he said and what he was producing seemed to make a lot of sense. Thinking about it, you only want to make it once, not having to re-visit the bearings routinely seems to be a good idea.

The other thing he does is to drill down the shaft to a cross drilling to provide grease to the bearing surface. Add a simple grub screw in the end of the shaft and job done for life. Also, it occurs to me that pushing the grease in to the middle will push any crap out the way it came in.

[KeithW]

Steve,
A very interesting letter.
Have you any information regarding the catalogue you mentioned?
I'd be very interested in replacing the bronze bearings on my partially built Torquay Manor, if as you say, do it once and forget about replacing.
I'm not too sure about the nitriding part though. I'd have thought that properly carried out case hardening would be more within the possibilities of us model engineers in the sticks.

Keith

[Tim Bayliss]

A word of caution on using needle bearings - they are designed and intended for radial loads ONLY. The use of an enclosed cage is to stop the small needle bearings falling out when assembling/dismantling, not as a method of taking axial thrust. Should your application constitute a degree of axial as well as radial load an additional bearing (a thrust type bearing) may well be required to protect the needle bearing.
A typical example of this situation would be the wheels of a locomotive where the main load would be radial, but at curves, points, etc., there would also be an axial element. Bronze bearings, if correctly fitted, could happily take this sideways thrust on the ends of the bush but a needle bearing could be 'popped' out of it's races.
A good use of needle bearings would be, for instance, big or small end bearings where there is a simple radial load.
Hope you find this info. usefull.
Regards,
Tim Bayliss

[SteveW]

I take the point about axial loading but at the end of the day the axial loads in our locomotives are going to be minimal and easily taken using a simple bronze/nylon thrust washer between the axle shoulder and bearing housing. A bit of float is necessary for going around tight corners anyway. My loco drawing set does not include any axial thrust considerations other than trapping the alxes between the lumps of bronze in the wheel hangers because they're there. QED.

As regards the catalogue/availability the pitch given to me was that these things are generally available through your local friendly bearing supplier (although I haven't checked as the shops were closed). It's certainly worth a ripple through the yellow pages and giving whoever a ring. I just did a Google search and got 'http://www.midlandbearings.com'. Some nice pictures but unless you've got broadband DON'T hit the price list link, its full of very big numbers and the prices look like part numbers. The product list is equally unhelpfull. Maybe there are other web connected bearing suppliers with a MORE browser friendly site.

As for the bearing surface again the quote was to choose the steel carefully. Many folk go for silver steel by default and as for the nitriding this I understand requires an appropriate steel to start with and the process is outside the range of the home user. Home case hardening without screwing up the dimensions is another science outside the home user as is simple tempering if you think about it. Again it's fingers do the walking.

If one of these engines is going to be a lifes work why screw it for the sake of a few quid.

Anyway, having reported in with this information it's down to the user to make the informed choice. I hadn't considered needle bearings, now it's on the list of 'to be considered'.

[SteveW]

In addition I've just noticed a whole bunch of bearing supplier adverts on my version above this posting.

Just watch out for that Midlands lot and their price list.

[IP]

Gents,

Nitralloy is a steel which can be nitrided but I bet you won't find a supplier willing to supply to the model engineer!

Also consider "Glacier" bearings which are white metal on the outside with nylon on the running face or opposite depending on the application. These bearings are cheap in comparison and will easily last the average locomotives lifetime!

Regards IP

[Deleted]

I have seen Timken combination thrust and radial needle roller bearings used in Axle box’s but how do they fair in coupling rods?

[ewal]

I would'nt have thought needle roller bearings were a good idea for coupling rods as the distance between the crankpins alters as the wheels move up & down individually, so they require a certain amount of slackness.

E.W.

[Deleted]

The slackness should be in the horns not in the axle bearings or crankpin bushes. The horn of the driving crank should be a nice sliding fit up and down. The others should also be a nice sliding fit but with an added slackness towards the driving crank.
One of the members build an 71/4 BR24 with roller / needle bearings all over. Works now for several years and is still running like a charm. Simplex, with bushes, is in the same period in dyer need of overhaul.
Regards
Wilfried Vermeiren
users.skynet.be/modelbouw.wilfried

[ewal]

You are right of course Wilfried but I don't think I could machine to such tolerences.

E.W.

[Deleted]

Believe me You can, see my recent posting under the tread of precision. I know chaps who never had worked metal in their lives and make now the most wonderful things. Just keep practicing whilst you are building something and always try to get it “spot” on you will notice it becomes a natural habit working this way.
Regards
Wilfried Vermeiren
users.skynet.be/modelbouw.wilfried

[ewal]

I certainly admire precision, but the reason I built large locos was because they are easier to build for a beginer & will run quite slack. However steaming the Garratt this afternoon I was aware of an embarrassing knocking on the rear offside, so come the winter I will attempt to fit roller bearings.

E.W.

[NZoldun]

Needle bearings require high finish, hardened and ground pin surfaces on which to run. The pins are essentially acting like the inside surfaces of a roller race and they definitely dont like any loading which tends towards the ends of the needles many years ago i designed needle rollers into a wool scouring machine - extremely dirty places. Even with proper seals each end they didn't last 12 months