Running needle roller bearings

Is it necessary to run needle roller bearings on hardened steel shafts?

I'm making a slow running engine (up to 200 rpm sort of speed) and the drawings show roller bearings on crankshaft and con rod ends. The two cranks are overhung on each end of the crankshaft. Diameter of shaft is 1/2" for main bearings reducing to 5/16" for the crank arm location.

I don't want to use hardened steel if I don't have to because of probable distortion when cooling, even if plunged end on.

If I can run on unhardened silver steel, I was considering eBay UK 222987986234 for the job.

Dave
The Emerald Isle

You may be able to get a thinwall sleeve from a bearing supplier for the needle roller to run on. I fitted one on a motorcycle gearbox shaft to repair it.

https://simplybearings.co.uk/shop/Bearings-Needle-Roller-Bearings-Needle-Roller-Inner-Rings/c3_29_35/index.html

Edited By old mart on 27/07/2021 17:12:53

Ideally you need a surface hardened shaft ground to good surface finish and lubrication. Details can be gained from the Schaffer web site, used to be Ina Bearings. Obviously you can get away with most things in non critical applications, low speed and low load but still lubricated. If you have room then obviously an inner race can be used.

If the shaft bis soft, it is possible that the rollers will brinell the shaft, when subjected to a repeated cyclic load.

In one instance the ratio between shaft diameter and roller diameter meant that the cyclic load was applied in almost exactly the same point every time.. The shaft suffered, and the design had to be altered.

Howard

You can get hardened rods, meant for running linear bearings on. These are surface hard and I'll bet you could at least face them with carbide, perhaps even turn shoulders.

Duncan, you can turn and face the hardened rods using carbide cutters. I used linear bearings when making the guide for the z axis DRO fitted to my Chester Super Lux milling machine. The swarf gets hot!, but given the small diameter shouldn't be a problem. The supplier advised the shaft was only surface hardened but on 8mm dia. in fact seemed to extend throughout the rod.

Robert Butler

Thanks for the suggestions, gents.

Because the engine will be slow revving, developing little power (hot air engine) I will modify the design and use gunmetal bushings. Lot less chance of um...mishap.

Dave
The Emerald Isle

You could look at sintered bronze bearings, available in metric and imperial, self lubricating and already made to size.

If it’s for a hot air engine where friction is your enemy would you be better to use ball races, much less contact area than needle rollers. And you can buy them with different clearances.

I think you will need to do everything you can to minimise friction, so plain bushes may not be the best idea. On the other hand. I very much doubt that the loads and speeds from a hot air engine would require hardened shafts if you wanted to stick to the original design.

You should be OK with Bronze bearings Dave, certainly worked OK in the Heinrici that I made earlier this year and that carries on running for a long time after the heat source is removed as does the Robinson with it's bronze bearings.

I'm going to go for the bronze bushings, and like the idea of the sintered bronze idea (Oilite?) One advantage is that they have a smaller overall dimension than needle rollers or ball bearings and this helps getting closer to scale full size dimensions and shape with the bearing housings.

(J.B. it's the Improved Rider engine.)

Dave
The Emerald Isle

Split bearings and wedges it is then

You may actually be better off machining the main bearings. Oilite etc are a bit oversize until pressed into a hole and you may not be able to close them down with the separate bearing caps and end up with a loose fit unless you turn the crankshaft to fit from larger dia stock

As the forces will be minimal and the minimum of friction is best for that type of motor, if possible, the shaft in the bush should be made a very light push fit at first and then polished down with 1200 or finer grit paper used with light oil until it fits with no friction at all. Every stage would need washing in solvent before testing the fit to avoid getting abrasives in the bush.