tolerance on shaft against mating bearing set tolerance

[dogbural]

Hi,

I have one example of drawing as attached.

Tolerance in red box is bearing tolerance; whereas the remaining ones are for shaft OD tolerance.
General tolerance asks for dia 60 is +/- 0.15mm

Considering requirement of interference between bearing set and shaft OD, what is the allowable tolerance of OD of the shaft?

59.999 - 60.000 ?

 

[drawoh]

dogbural,

If your shaft must rotate in the bearing, there cannot be interference.

Is this a journal bearing, or are you using an interference fit with the inner race of a ball bearing?

--
JHG

 

[3DDave]

If it is a ball bearing then there is often a need to have no clearance to prevent the shaft from rolling inside the bearing or for the outer race to roll within its seat. Shaft locking compound can be a help in avoiding this situation.

If that is the bearing tolerance and the note is correct that this is a select fit, then the shaft can vary from 0.000 over the minimum and 0.003 over the maximum - so 59.997 to 60.002; not all bearings will work with all shafts.

 

[geesaman.d]

Wow, so the bearing bore has a two micron tolerance, and the final fit has a three micron tolerance. Those must be high precision bearings.

If you can grind to a 1 micron tolerance, you won't need to match anything. Keep your shaft diameter 59.999 to 60.000 and you'll have the .000/-.003 finished interference. If you can't hold a micron, then you'll need to measure every bearing set for its actual bore diameter and match the shaft with a fitting bearing set. That'll gain you another 1 micron or so for the shaft diameter tolerance. (Do the bearings come with bore diameters pre-measured? That step seems like something the bearing supplier would be best equipped to do)

I don't know what bearings this uses, but if they are paired / matched angular contact bearings, then they come as a pair with very closely toleranced axial clearance. The shrink fit to the shaft directly affects the axial clearance. In some cases (TDO taper roller bearings), it's easier to adjust the spacer in between the bearings to obtain the final axial clearance, which allows more tolerance range on the interference with the shaft.