Roller Bearing Tolerance: Machinerys Handbook

[Uglydog]

I've been asked to make 4 steel wheels for the city.
Their original spec was 5inch wheels with .5inch grade 8 axles/bolts on sealed bearings.
Something about using it to haul stuff from the garage to the ice rink for the Zamboni. It's unclear how much they plan on loading onto this little cart. Somewhere between several hundred and several thousand over occasionally irregular surfaces (read occasional impacts). We won't talk about if a rubber tire is more appropriate. Regardless slow speeds... very slow. I talked them into moving up to a .75inch grade 8 shaft and a larger bearing.

My question: What should the OD for the bearing be?
I've been studying the Machinerys Handbook and can't find the answer. Likely a user error....
Perhaps I'm overthinking this...
To tight and I potentially crimp the bearing preventing the axle from turning. To loose and I'll get bearing creep. Yet the two bearings need to align so that the axle spins. What do I need for tolerances for all these factors?

Truth is my question is multi fold: 1) what are my tolerances, 2) where could I have found this in the MH. I've read about press fits and bearings. ANSI, British and Metric. Lots of cool stuff. Just can't find the answer to the confusion. Please feel free to be critical my entire thinking of the problem and by drawing (other than it's not in CAD ).

Thank you,
Daryl
MN

 

[Bob Korves]

Daryl, I would use metric bearings, just my preference, but better availability and prices for good quality bearings. YMMV. The easiest way to build it is to bore the wheel through to the OD of the bearings with a snug sliding or very slight press fit, cut two snap ring grooves to retain them, and then make tubular spacers for both the inner and outer races to the same accurate length to fill the spaces between the bearings. The mounting bolts with compress it all neatly together.

 

[Bob Korves]

I've been asked to make 4 steel wheels for the city.
Their original spec was 5inch wheels with .5inch grade 8 axles/bolts on sealed bearings.
Something about using it to haul stuff from the garage to the ice rink for the Zamboni. It's unclear how much they plan on loading onto this little cart. Somewhere between several hundred and several thousand over occasionally irregular surfaces (read occasional impacts). We won't talk about if a rubber tire is more appropriate. Regardless slow speeds... very slow. I talked them into moving up to a .75inch grade 8 shaft and a larger bearing.

My question: What should the OD for the bearing be?
I've been studying the Machinerys Handbook and can't find the answer. Likely a user error....
Perhaps I'm overthinking this...
To tight and I potentially crimp the bearing preventing the axle from turning. To loose and I'll get bearing creep. Yet the two bearings need to align so that the axle spins. What do I need for tolerances for all these factors?

Truth is my question is multi fold: 1) what are my tolerances, 2) where could I have found this in the MH. I've read about press fits and bearings. ANSI, British and Metric. Lots of cool stuff. Just can't find the answer to the confusion. Please feel free to be critical my entire thinking of the problem and by drawing (other than it's not in CAD ).

Thank you,
Daryl
MN

View attachment 118829

Bearings need to be able to align themselves in their mountings. Typically, one side, the bore or the O.D., is a press fit and the other is a sliding fit. Standard practice is for the rotating side to be the press fit, but that is variable, based on temperature swings, dissimilar materials, and a whole lot of other factors. For slow speed stuff at room temperature with similar materials all around, just make one or the other half of the bearing able to move axially to align itself. Otherwise the bearings will be in a bind and will die an early death. Press fits are not critical to your application.

 

[bfd]

go to someplace that sells skf bearing and see if you can get a copy of the skf bearIng handbook. it has all the required fits and clearances. It was very helpful when you are working wIth bearings bill ps there are different requirements for different applications motors, high speed, high load or both highspeed and high load, also low speed high load. so you need to decide what you have and look at the right chart. maybe high load and slow speed. there are very expensive bearing books 3 separate book tell you everything you need to know about bearings. bill

 

[Wreck™Wreck]

-.001" on the bore MAXIMUM, I do hundreds of bearing bores per year in that size range, a tighter press fit will likely cause problems.

If you do not have one buy a dial bore gauge or you will be shooting in the dark. A person with skill and experience can get within .001" with a telescoping gauge and a mic, however it is time consuming.

 

[Andre]

You say they're for high radial load. What about needle bearings? They will handle impacts better than radial ball bearings because there is more surface area between the needles and races. They won't notch and click as easily.

EDIT: Or, cylindrical roller bearings. Same thing only different....