How to assemble this shaft & bearings?

borne2fly · Apr 17, 2019

All three bearings are a light press fit into the housing, and a light press fit onto the shaft. To put it back together, it would seem like I first need to press each bearing onto the shaft one at a time (pressing on the inner races), then press the whole thing into the housing. But how is the second part done without some of the bearings getting pressed into the housing via the shaft? At that point I'd like to apply pressure only to the outer races, but it seems you'd need to do all three simultaneously. Is there some special assembly trick for this sort of thing? This is the input shaft from an old L&S lathe. Someone suggested I heat up the housing with a torch, but that headstock is a massive thing and I can't believe the factory did that. Any ideas?

johansen · Apr 17, 2019

seems to me you can push the first bearing into the bore. then press the shaft into the bearing. you said light press fit. so you can just push it in. (6203 bearing might be able to handle 500 pounds axial thrust no problem. but a sharp tap with a hammer can exceed that!)

you then press the second bearing on the shaft and into the bore at the same time. a washer of the right id and od can press on both od and id of the bearing at the same time.. using a pipe as a sleeve to hammer it in.

The third bearing goes on the same way.

Tyrone Shoelaces · Apr 17, 2019

Without seeing the housing this is all a bit of a guessing game. However I'd install the centre bearing into the housing then slide/drive the shaft through it, fitting any gears as you go. Then fit both of the outer bearings from the outside.

Regards Tyrone.

Milland · Apr 17, 2019

Freeze the assembled shaft and bearings, after having given everything a good coat of grease. You'll still get some condensation as it warms, so coat the inside of the housings with oil or grease too.

If you go this route, after the shaft has warmed back to room temperature be sure to allow the spindle an hour or so of running at low RPM to flush excess grease from the bearings before any high speed running.

This questionable advice brought to you free of charge...

muckalee · Apr 17, 2019

I would do as suggested by Tyrone and fab a guide bushing for each outboard bearing to align and keep the shaft aligned curing assembly. The guide bushing would be a slip fit id and od.

HuFlungDung · Apr 17, 2019

borne2fly said:
All three bearings are a light press fit into the housing, and a light press fit onto the shaft. To put it back together, it would seem like I first need to press each bearing onto the shaft one at a time (pressing on the inner races), then press the whole thing into the housing. But how is the second part done without some of the bearings getting pressed into the housing via the shaft? At that point I'd like to apply pressure only to the outer races, but it seems you'd need to do all three simultaneously. Is there some special assembly trick for this sort of thing? This is the input shaft from an old L&S lathe. Someone suggested I heat up the housing with a torch, but that headstock is a massive thing and I can't believe the factory did that. Any ideas?

View attachment 254679

Don't confuse a light press fit with a push fit. A bearing cannot be pushed by hand onto a shaft or into a bore without at least .0002" clearance. With zero clearance, it is still tight seeming. Most of this phenomena is due to our human inability to really align things so that they don't go together at some cocked angle. If you get things aligned, then often you discover that the light press fit was actually a slide fit that you can actually pull apart quite easily. This proves that a lot of force is not required for assembly and if you do use a lot of force than you are probably spoiling the fits permanently with gouges and score marks.

Measure everything accurately and you will know what you are dealing with.

borne2fly · Apr 18, 2019

All good advice, thanks everyone! I didn't know you could press the inner and outer races simultaneously, but I guess if both are press fits then there isn't much choice. Looks like I'm going to be making a few guide bushings.

Illinoyance · Apr 18, 2019

Bearings are normally fitted with an interference fit on the rotating component and a small clearance fit on the stationary component. I bet that is what you have. Freezing the shaft will make assembly easier.

wippin' boy · Apr 19, 2019

insert first two bearings in housing
freeze shaft
slide shaft in
tap last bearing into place using push device (proper size chunk of pipe) on inner race

AHUNT · Apr 25, 2019

I'm a fan of using temperature to your advantage on this one. If you have good gloves, you could also stick the housing in an over too to make it a hair larger.

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How to assemble this shaft & bearings?

borne2fly

Hot Rolled

johansen

Stainless

Tyrone Shoelaces

Diamond

Milland

Diamond

muckalee

Cast Iron

HuFlungDung

Diamond

borne2fly

Hot Rolled

Illinoyance

Stainless

wippin' boy

Diamond

AHUNT

Plastic

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