fitting bearings to a shaft advice

[marbles]

Are you sure he didn't mean 5 thousands? Aka 0.127mm.
In which case, it's going to be one very tight pressfit, which will most likely lock the bearing so it doesn't spin.

Thinking back I think he said "5 thou". Ok, if we assume its 5 thousands with bearing expansion and freezing the shaft will that not give the spacing to get them on?

[m_c]

Thinking back I think he said "5 thou". Ok, if we assume its 5 thousands with bearing expansion and freezing the shaft will that not give the spacing to get them on?

Not likely.
Even if you did manage to get it on, it's highly likely the bearing will seize due to the pressure expanding the inner race. I don't even think an increased clearance bearing would even be able to handle that much expansion.

[Neale]

Yes, 5 thou is definitely too much. Half-thou is not quite as much as the usual "thou per inch" rule of thumb, but then you are heating the bearing and I'm not quite sure how hot you can reasonably make that. The other useful trick, assuming that you are fitting two identical bearings, is to turn down the central area of the shaft to give a thou or two extra clearance everywhere except the areas where the bearing rings are going to sit. That means that the bearing that has to go on furthest has less chance to grab/jam partway down. You could also make it easier by finding a reasonably close-fitting tube that fits over the shaft with a square end and use that to push the bearing (pushing on the inner race) to try to maximise the chance of it staying square.

I'm not quite sure why Spluppit recommends tallow specifically over a more conventional (and easier to find in the workshop?) grease - I would be interested to hear. That's not a negative comment - I have just not heard of that before and I'm curious.