Ball bearing axleboxes

[Phill SpowartParticipant @phillspowart84010]

Axlebox question: I'm tentatively starting on a 5" gauge Stirling single. I want to redesign the bogie axleboxes to use ball bearings. 12x18x4mm ball bearings look a good size to use. My question is, should I have one bearing in the centre of the axlebox, or would it be better to have two? I'll be fitting rubber seals too, so shouldn't be any problems with grit and muck getting in.

Edit-Or, I could use a 12x18x12 needle bearing plus two seals?

Edited By Phill Spowart on 01/03/2018 18:40:00

[Phill SpowartParticipant @phillspowart84010]

[nigel jones 5Participant @nigeljones5]

I have used a single bearing in the past – not going for two as they can add a little too much drag with the pre installed seales. I used the sealed for life ones. I asked our engineers at work about using the caged needle rollers but they advised against them citing that they would fail long before the 'normal' bearing does. Hope this helps.

[Phill SpowartParticipant @phillspowart84010]

Cheers, my plan is to have the bearings themselves unsealed, and use separate lip seals on the axle. I can then machine a recess in the axlebox for an oil bath. Pop in a fill and drain plug, and hopefully I'll get the least possible rolling resistance.

[duncan webster 1Participant @duncanwebster1]

You can get shielded bearings, which have a sort of labyrinth arrangement, much less drag than rubber seals. If not actually under firebox I'd go for 2 of these, singe side shields and fit a grease nipple to give them a squirt now and again. 61701Z is the part #, you probably have to get ZZ and prize out the seals one side.

[Ian S CParticipant @iansc]

If you are going to grease the bearings, you must prevent contamination in a dirty area of the loco, any thing from the ash pan mixed with the grease will cut the bearings out in no time. I'd leave the seals on, and have the axle arranged so that bearing replacement is possible. How hot does that area become during a days running.

Ian S C

[Neil WyattModerator @neilwyatt]

Needle bearings are well proven in model loco designs and they usually fit in scale axleboxes and run well on as-bought precision ground axles.

Loads are a fraction of what woudl normally give a standard 1,000,000 revolution life.

Neil

[Andrew TinsleyParticipant @andrewtinsley63637]

Full size practice on the few engines that were so fitted, were Hoffman roller bearings. So needle bearings would be an equivalent?

Andrew.

[Phill SpowartParticipant @phillspowart84010]

Here's what I'm thinking of, this is a tender axlebox. Just realised I should have drawn the hole blind, not through, but you get the idea.

Green is a viton lip seal, red are ball bearings (2 per box), blue is a spacer for the internal races. The loco boxes would have a viton seal each side.

Not shown are oil plugs top and bottom. The gap round the spacer would be the oil reservoir, boxes would be filled after fitting on axles but before fitting into horns. My intent is that with the oil sealed in, it cannot escape while dirt is kept out. I'd have to drop the wheels out every so often for oil check/change.

[Speedy Builder5Participant @speedybuilder5]

So what happens if the left hand wheel tries to drop further than the Right hand wheel ? I would have thought that you would need self aligning races if you are going for that sort of precision.
BobH

[Phill SpowartParticipant @phillspowart84010]

Posted by Speedy Builder5 on 03/03/2018 18:15:13:

So what happens if the left hand wheel tries to drop further than the Right hand wheel ? I would have thought that you would need self aligning races if you are going for that sort of precision.
BobH

The clearance in the hornways would allow for that I think? It's how I've seen it done on full size narrow gauge practice. This is why I'm posting though, far easier to find the flaws before I build it

[Phill SpowartParticipant @phillspowart84010]

Also, wouldn't you get the same problem with needle bearings?

[gerry maddenParticipant @gerrymadden53711]

Here is a typical Hoffman axle box. This one was fitted to underground stock but the internals were the same on boxes fitted on things such as the Class 31. The two rows of rollers carry the journal loads and the bronze pads carry the thrust from the axle.

[gerry maddenParticipant @gerrymadden53711]

oh and they are grease lubricated, yes, including the thrust pad !

ps this picture isn't very good I wonder what I'm doing wrong…..

[Phill SpowartParticipant @phillspowart84010]

Thanks for that. My thinking is that the ball bearings will take the side loads, but other than that it looks pretty similar?

[gerry maddenParticipant @gerrymadden53711]

Yes two ball bearings side by side will be absolutely fine in your case. Its sensible to put a small spacer between the inners. Just be careful that you don't nip the outers when you secure them axially. I wouldn't bother with oil though. Use ball bearings with a single metal shield and position the shields on the outsides.

[Phill SpowartParticipant @phillspowart84010]

Yep, was going to keep the outer shields on the bearings, with the separate seals as well it should be leak proof.

I was thinking oil would give less resistance, and be able to flow better into the bearings. In full size the grease gets forced in by gun, whereas I have no intention of making a 1/16 scale grease gun!

When I get myself organised, I'll start posting how it goes. Quick bit about me-this is my first proper attempt at a steam engine, but I've been a machinist in full size for a good 12 years-trams, jet engines and classic bikes. I did start on a Tich, having bought a rusty rolling chassis but after making a few bits I decided I'd rather put the effort into something more interesting. Much as I love LBSC's writing, his methods are very much of their time (imagine his joy at finding his local supermarket flogging ok-ish digital calipers!).

[gerry maddenParticipant @gerrymadden53711]

The picture wasn't so clear in the earlier post. So here it is again. A little better I think.

Regarding grease, yes there will be a little more friction than with oil but it will still be small compared with your seals. And once the grease in the bearings has 'channeled' (might take a few thousand rotations) the friction will drop to a level much closer to that of oil anyway.

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