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TR
09-21-2011, 08:25 AM
This may be obvious to many, but if I have a 15mm diameter shaft and want to make a bush which slides over it easily, but is not too lose or too tight, what size do I machine the hole in the bush ? I know it must be greater than 15mm but by how much ?

J Tiers
09-21-2011, 08:37 AM
Somewhere in the 0.05mm to 0.1mm range it will start to seem sloppy.

At around 0.25 mm it will go over reasonably easily and will have a hint of slop. With oil it will be a "quality" fit, and reasonable running clearance.

This depends on length.... I am basing on about a 12-15mm long bushing, i.e. roughly equal to the diameter.

David Powell
09-21-2011, 08:49 AM
How long is the bush intended to be? What is the material and more importantly how straight is the shaft and what is the surface finish? What is it for--- a rock crusher or a clock? What conditions is it expected to work in- a sterile temperature controlled room or in a hostile dirty environment? My wag( Wild ass guess) given a bush 25 mm or so long riding on a ground mild steel shaft would be to give it about 0ne thous clearance, or a little less as a minimum and maybe up to four thous as a maximum that is bore your bush 0.02 mm over 15 mm to0.08 mm over 15 mm. Obviously the less clearance the less shake but other factors may well affect the needs of the job. If the bush is to be press fitted into a housing or outer shell then the amount it will close up when fitted will have to be allowed for, or it will have to be bored or reamed out after fitting in its housing. Hope this helps. Davd Powell.

TR
09-21-2011, 08:55 AM
Good comments. Got me thinking. The shaft is a motorcycle axle and the bush is more or less a place holder. One side has two bearings and the other 1.
circlip+B+B+bush+B+circlip

moe1942
09-21-2011, 09:19 AM
Sounds like a running fit. Consult machinerys handbook in the interference fits section.

Ian B
09-21-2011, 09:53 AM
It sounds like it's a spacer. Normally, the bore of such an item wouldn't be critical, but the length would. The spacer needs to be at least a sliding fit, maybe looser. I'd bore the hole until the shaft just goes in, then open it up another 5 or 10 thou.

I've seen bits of seam welded water pipe used in this type of service, and they fitted where they touched. Worked just fine...

Ian

Jaakko Fagerlund
09-22-2011, 04:01 AM
If your axle is 15.00 mm (h9 or h11), then a 15H7 reamer makes a perfect running fit for it. But if that piece is a spacer, I would just drill/bore it to 15.1 and be happy.

.RC.
09-22-2011, 04:36 AM
A sliding fit so when water gets in there it won't rust into a solid immovable mess....

I take it the spacer does not spin and is stationary, so go for a 1mm clearance...

philbur
09-22-2011, 05:27 AM
http://www.engineersedge.com/general_tolerances.htm

Google really, really, really is your best friend.

Phil:)