Help with tolerances for a small spindle project

Sourced some parts for a small spindle project and would like to get some feedback on the tolerances. All steel parts of different high tensile qualities however not hardened (I think..). Housing is to be ID 80mm throughout and shaft is to be OD 40mm. Was planning to use 2x double angular contact bearings in the front and 1x ball bearing at the back, all greased. C-C distance between the two bearing positions is to be approx. 125mm. I'm not having high expectations so my goal is for now continous 5-6K rpm with 0,05 runout at approx. 50ºC.

As I wish to use available off the shelf components to keep the cost low and DIY factor high I have ended up with tolerances as stated below (both ID housing and OD shaft = Ground).

Do you guys think my clearances below are OK?

Between housing and outer bearing shell:


Between inner bearing shell and shaft:

Anyone?

Would really appreciate some feedback on the tolerances.

I'd probably shoot for .02mm interference on the shaft, and 0 clearance on the OD fit in the housing. You might give the housing .01mm clearance to make assembly practical, but you should have a lock ring to preload the outer races and retain them in position. Same for the inner races on the spindle.

You might post a sketch of the cross section of the entire spindle housing, bearings and spindle for review for better recommendations that apply specifically to your design.

It would help to let us know what the application for the spindle is, as that would drive most of the recommendations for bearings and clearances. Stiffness, whatever is getting attached, dust and debris shielding, lifespan, etc. will all contribute to best approaches.

The bearing mfrs catalogues have a huge resource of information, any tolerance you could think of, both for the bearings and housings and shafts.

The SKF version I was looking at also had examples of different spindle arrangements for bearings. Lot of info on stiffness of different setups as well. Also stuff on seals, labyrinth seals etc.

Tables of tolerances don't help much with the practical aspects of design, they will more allow you to get a picture the latitude in dimensions of a batch of acceptable parts.

The more practical aspects of designing parts comes down to this: "How will it be assembled and what if it must be disassembled and reassembled again with the same bearings?" "How must I design the assembly so as to avoid unwanted preloading of bearing elements during assembly?" "How must I design the assembly so that intended preload can be given?"

A slide fit is pretty well standard at .01mm to .02mm clearance, no matter what the size of the bearing. A broader tolerance range won't make a better fit, even if 'allowed' in a bearing catalog. They will tell you what size their bearings will most likely be, that you can rely on, but if they come in at 'max' and your part comes in at 'min', you might still have assembly issues (too tight) or wear-life issues (too loose). So then it comes down to the final fitting, where you work on the fits to make them ideal for a spindle and housing assembly.

Get down to zero clearance and you're getting into heating/cooling/pressing assembly/disassembly methods. Is that practical in your particular instance?

Get into interference territory, then you become more concerned with ultimate housing and shaft roundness, as the bearing conforms to the shape it is fitted into/onto. You also do not want to eliminate the internal clearance of a bearing designed to have some. Again, a tolerance range doesn't help much except to give an excuse for a premature failure of the assembly if exceeded, but doesn't really nail down what you should have used.

I bore and sleeve a lot of bearing seats in electric motor endbells. I see all kinds of 'factory tolerance' on these things, all erring on the + side. They got away with as much as .1mm clearance (in the warranty period) on a slide fit that I redo at .01mm clearance. Guess what: the loose tolerance isn't a very good fit, but it was in someone's 'tolerance table'. Doesn't mean jack shit.