Needle Roller Bearing Axleboxes

[baggo]

I mentioned in a previous post that I will be fitting my Simplex axleboxes with needle roller bearings. I've done a bit of research and Arc Euro Trade Ltd (usual disclaimer) sell a suitable size for £4.75 inc VAT. The bearings are 3/4" bore, 1" od, and 3/4" wide and fitted with rubber seals at each end (part No. JTT1212). Your local bearing stockists will no doubt sell them as well.

I've done a quick sketch of a possible modified axlebox to accept these bearings. The box to be bored through 3/4" clearance and then counterbored 1" dia to a depth of 3/4" to take the bearing. This does leave the axlebox a bit thin at the top (like me ;D) so it may be advisable to make the slot in the horns a bit deeper (if the castings will allow it) to enable the axlebox to be made a bit taller (1/16"?). In order to give the bearings an occasional dose of oil or grease, the axles can be drilled at the ends and a small cross hole drilled to feed the oil/grease to the bearing.



Note that the bearings have to be a press fit in the housing to give the correct running clearance. Ketan Swali of Arc Euro wrote a letter to ME about bearing fits and a copy can be seen on their website
www.arceurotrade.co.uk/ under projects and articles:

I use silver steel for axles but ground mild steel should also give a very long life as the wear should be negligible.

The only problem with using needle roller bearings is that if you are not careful the chassis rolls off the bench as soon as you turn your back! You'll find that the chassis is so free until you start fitting the motion that it will roll down the slightest incline.

The 2.5" gauge 4-8-4 tank loco I'm building at the moment has needle rollers on all 8 axles with the two rear coupled axles running in sealed Cannon type axleboxes. Both these axles are under the grate so this should keep ash and grit out of the bearings.

John

[SteveW]

John,

Re your drilled axles: A while back I saw a similar idea but the guy had opened out the end to include a spring, a small ball bearing and a screw in plug with the oil hole in the centre. The point being you oil through the little hole in the end plug into a now enlarged reservoir and the spring and ball keeps it in and any crud out.

[Steve M. W]

Well done thanks for the posts, think I will fit needle rollers if I can rebore my axle boxs this is just the sort of input we need
Thanks again

Steve

[Chris Kelland]

Hi John,

I was talking to a fellow Simplex builder at the track yesterday and we talked about this and I can now see that it can be done. Many thanks for the post. My previous thoughts were to make the axleboxes split. I am currently trying to give the club Simplex its third new life and having split boxes has made work on the axles and motion very easy.

Chris.

[baggo]

SteveW,

I was a bit concerned about the problem off crap getting into the oil hole and thought about just putting a plain screwed plug in but your suggestion re the spring loaded ball seems a much better idea! Thanks for that.

Chris,

Hopefully fitting needle rollers will mean that replacing axleboxes etc. will be a thing of the past! If you are going to fit plain axleboxes then the split ones are the way to go, certainly in the larger gauges. Martin did mention using them in the Simplex articles but I think he perhaps considered them a bit fiddly for a beginner to make.

My drawing shows the bearing fitted at one end of the axlebox but it could be centralised by making the counterbore deeper and perhaps fitting a thick washer in the resulting recess on the outside. Actually the width of the axleboxes could be reduced with the needle rollers fitted but this would mean reducing the thickness of the horns as well. Martin deliberately made the plain boxes wide to reduce the rate of wear.

John

[ron]

John
Have you looked into whether 'sealed for life' bearings that size are available?
I like your idea, I think I will probably fit them as well.
Ron

[baggo]

I'll have a look Ron but the problem is keeping the thickness of the bearing as small as possible, otherwise the axleboxes will have to be made much bigger. The advantage of the drawn cup needle rollers is that you can use them without an inner race and run them directly on the axle. The bearings mentioned have a rubber seal at each end which will keep the oil/grease in and the dirt out so they should be ok. An occasional shot of oil/grease will keep them in good order and force out any rubbish that does get in.

John

[greasemonkey]

Hi All
I like the idea although my chassis is to far advanced for me to change it, however I was under the impression that you need to have a hardened and ground axle for closed cup needle rollers if you are not using an inner race. I found this on the SKF website that seems to support this thought
www.skf.com/portal/skf/home/products?paf_dm=shared&maincatalogue=1&lang=en&newlink=1_5_1x
and from experince on a bogie riding trolley I had to modify as a result of the axles and bearings getting chewed up by not having a hardened sufarce to run on.
Are you counter boring the inner face for the needle rollers so that the outer face still acts like a 'thrust' washer against the back of the wheel?

Andy

[ron]

Andy
I agree with you, the axle would definitely need to be hardened and ground to resist wear, it's a similar set up to the layshaft bearings in a car gearbox that uses needle roller bearings which only have an outer race, the layshaft is [case?] hardened and ground to suit,
Ron

[greasemonkey]

Hi Ron
Any thoughtds on how to do it? Silver steel would harden all way through and become brittle, what about using some EN42 and geting it Nitrided? If you used En1 would it be sensible to normalise it first before machining to relive the stresses otherwise it might go bannana shape whilst being case hardened. Or am I just being paranoid?

Andy

[baggo]

Hi Andy, Ron

This subject was discussed at length in ME (Postbag) in early 2005 and the general opinion by the writers using needle rollers was that silver steel or even mild steel would give satisfactory service and the axles/bearings would probably outlive the loco to which they were fitted (probably the owners as well!). True, the manufacturers recommend using hardened axles but that is to carry the design load which may be several tons per bearing! In our use the loads per bearing are going to be nothing like this. Just divide the weight of the loco by the number of bearings. The result will probably only be 10 to 30 lbs per bearing. Also the load is spread over several rollers at a time so the load per roller becomes even less. They are also rated for much higher rotational speeds than they will ever encounter in a loco.By all means use a hardened steel axle but obviously this will make the job a lot more complicated with regard to machining and finishing the axles. Another possibility of course is to use the hardened inner races as well but this means either reducing the diameter of the axle or increasing the size of the housing.

Obviously the loads on the bearings of a driving trolley, especially if of the two axle type will be higher due to the weight of the driver etc. so this may be a situation where hardened axles would be beneficial. Is it possible that the rollers were skewing in the outer shell instead of running true, thus causing the failure? This can happen if the axle is too sloppy a fit.

Yes, the axlebox can be counterbored from the inside to leave the outside at 3/4" bore but there will probably be enough area left to act as a thrust face even if bored from the outside. I found this with the 4-8-4 loco which has the bearings fitted from the outside. One writer suggests fitting an 'O' ring in a recess on the outside of the axlebox to act as a thrust washer.

John

[ron]

John, I find it hard to believe mild steel would last very long with a roller bearing running directly on it, silver steel maybe but I still think some sort of hardened surface would be better, after all if it does wear rapidly it's a helluva lot of work to rectify.
Ron

[greasemonkey]

Hi John
I agree with Ron, the driving trolley I had was built by me and was a semi scale SR well trolley running on two bogies. I weigh 165lb, which was spread over the 8 axles giving a weight on each axle of approx 21lbs, running on journals 10mm diameter. They lasted 2 months before replacement and I put hardened collars on the ends of the axles.
The simple fact that one writer even suggested using O rings as a thrust washer says it all they werent designed for that job and are totally inappropriate.
On Simlex the only area that is availble to take the axial thrust on the back of the wheel is the central boss, which at approx 1" daimeter doesnt leave much for a thrust face if you insert the bearings from the outside. If you use sealed ball races which are a press fit on the axles and make the axle boxes with a plate that keeps the bearing captive you can do away with the outer flange and the bearing takes the axial thrust. End play is then controlled by the dimensions of the axle box/horn guide back to back dimension and not by the end float of the wheel set.
Simplex is an engine that was concived to be a hard worker hence the generous bearing surfaces. The addition of needle rollers is a natural progression on from where Martin left of, but with modern technology and methods availble to us now it has never been easier to produce a corretly engineered result that will out last it builder. I sometimes wonder why people follow the practises of the early pioneers in Model Engineering to the word and dont employ modern practise and materials were appropriate. As Ron says its a lot of work to correct when it all goes wrong.

Andy

[baggo]

Hi Ron,

I'm having a search around to see if I can find some suitable hardened steel shafting. There was a letter in ME from a chap who suggested SKF make a hardened steel shafting available from RS. I've had a look on the RS site and they do sell hardened stainless steel shafting for use with linear bearings. It's only available in metric sizes though i.e. 16mm or 20mm dia. It's supposed to be made by SKF but I can't find any reference to it on the SKF website! It's a bit pricey though - about £50 per metre! Then there's the problem of cutting it to length.

I think the easiest way is to fit a complete bearing i.e. one with the inner race as well. This would mean reducing the ends of the axles to about 5/8" (or 17mm) dia. but I don't think that would be a problem.
Arc Euro do a 20mm ID x 26mm OD x 20mm long bearing with a 17mm ID x 20mm OD inner ring to suit. That bumps the price up to £9-50 per bearing though. I shall stick with the silver steel though, if only to see if it is suitable ;D

John

[greasemonkey]

Hi John
I would love to be proved wrong so let us know how you get on! I shall investigate the Nitriding route as that woiuld appear to be the easiest way. I may even change my chassis at this rate for comparison purposes.
Just had a quick look in the RS catalouge and you can get Needle Rollers with an inner ring. OD is 24mm ID is 16mm more expensive but it takes away all the problems, machine your axle to suit the ID of the bearing plus a fitting allowance, place axle in freezer over night, inner ring in oven at 100 deg C and when ready shrink fit together.

Andy

[baggo]

Hi Andy,
Using the inner race does get around any problems. It will be interesting if we all do it different ways so we can compare results!
Only problem is, how many years will it take! ;D.
When I get around to building my driving trolley I'm going to fit it with a milometer (probably using an electronic bicycle one with the magnet and reed switch) so that I can keep records of how many miles each loco has done.

John

[SteveW]

John,

A long while back I opened a thread here on someone I met using needle bearings on, think, all shafting and including the big ends. From memory he used one of the hardening steels and maybe nitriding. There was a similar discussion and some doubt about the suitability of needles for reciprocating applications.

(Update: Just found it "Using Needle Bearings" September 2004. Blimey that was a while ago.)

A thought I've been entertaining along the lines of hardening shafts for needle rolls is to try work hardening in the lathe using what in effect is a clamp type tool a bit like a clamp knurling tool but with a couple of butch ball races to crush the surface texture. The effect would be similar to plannishing armour.

[ron]

What about case hardening the ends of the shaft? I seem to remember when I was an apprentice there was a 'cyanide bath' at the hot end of the workshop, don't remember much about it, I used to give it a wide berth, but it was used for case hardening low carbon steel, presumably there is a modern and safer method of case hardening?
Ron

[baggo]

Steve,
I can't find the post that you mention but I was reading one of Keith Wilson's pages last night about needle rollers in coupling/connecting rods. He says they are ok to use on the driving crankpin as there should be not be any play in that bearing but definitely not on leading and coupled crankpins due to the clearance that has to be left on those to allow free running. Apparently the irregular motion imparted to the roller bearing would quickly destroy it.

Ron - I had thought of case hardening. It would be worth trying it on a dummy axle to see if it would work. Only problem with the usual way using Kasenite is that you've got to heat the metal up to bright red!

I've now read everything I can find in ME on using needle roller bearings - and everybody seems to use silver steel! Neville Evans uses it on all his locos in conjunction with the sealed needle rollers and says he has never experienced any problems with wear. He calls these 'sealed for life' so presumably it is not necessary to provide any outside means of lubrication. One point he does make, and I've read this before, is that it is very important not to OVER LUBRICATE the bearings on assembly as too much grease or oil can build up high pressures in the bearings and damage the rollers. He recommends just a light smear of thinnish grease on final assembly.

At the end of the day it's up to the individual as to what material is used for the axle but I'm quite happy that silver steel will do the job .

Just as a matter of interest I think I will set up a test rig using a motor to drive a silver steel axle and run a bearing on it loaded with weights to simulate actual working conditions. I'll just leave it running and see what happens!

John

[baggo]

Just had another thought. Keith Anderson posted a thread about used computer parts earlier. I reckon the slide bars out of old printers that the print head runs on would make excellent axle material if you can find some the right size. The finish on them is excellent. I've just tried filing one and although it is soft enough to file I reckon the surface is probably hardened to a certain degree,

John