Shaft Clearance for Pillow Block Bearing 4

[Frontier12]

We are rebuilding a piece of equipment that originally had a Dodge P/N 123813 pillow block bearing attached to a shaft. The original bearing and shaft were damaged badly and obtaining reliable dimensions is not an option. The Dodge website says this bearing is for a 1.4375 in. shaft.

How do I determine machine tolerances for a shaft that will work with this bearing? Are there charts available or is this something that I would need to calculate?

 

[TugboatEng]

ISO-286 lists the various tolerance ranges for shafts and housings.

You need to identify which tolerance best suits your application. From there, SKF has charts their website which will help you specify an allowable range of shaft dimensions.

If I assume correctly that the bearing needs to slide freely on the shaft for installation then you'll want to specify f6 for the shaft size tolerance.

 

[hydtools]

What does Dodge require?

Ted

 

[3DDave]

It should be in here somewhere:

https://www.farrellbearings.co.nz/site/farrellbearings/files//Dodge Catalouge 2007BEARING_WEB.pdf

 

[hydtools]

From the Dodge catalog for one series:

Ted

 

[TugboatEng]

OP posted a set screw mount bearing. OP needs clearance hence the f6 fit. OP may experience longer bearing life if they select a bearing with a light interference as preferred for inner race rotation loads. Straight diameter shafts make installing such a bearing challenging.

 

[Frontier12]

Thank you for all of your guidance!

 

[Tmoose]

Is this belt driven equipment, and was the bearing and shaft damage near the belt drive ?

The powerful and relentless radial loads from belt drives are very effective at overcoming set screw and eccentric collar type locks used on commercial pillow block bearings.

 

[3DDave]

The force on the shaft is oscillating in a belt drive - each half-turn changes the load direction and alters the condition from surface tension to surface compression.

 

[TugboatEng]

True, I was picturing it from a housing perspective. Scratch my above comment.

 

[geesaman.d]

Damaged shaft journals are extremely difficult to manage unless you pull the shaft, straighten, and spray weld and grind the journal back to original specs.

Every bearing installed on a worn shaft will fail like the original with shorter and shorter service intervals. I have customers who expect us (OEM) to have instant answers to get running again instantly on a worn shaft, but physics doesn't work like that. Use the Dodge catalog values for acceptable shaft tolerances.

Maybe you can install the new pillow block a few inches down the shaft onto fresh metal and choose a design with a more robust connection. As already mentioned, set screws on sleeves have very limited load capacity and I will add they are sensitive to differences in thermal expansion.

Check your belt tension. Belts sometimes have installation forces printed on the belt box but that is a worst case load. The optimal belt tension for the application can vary quite a bit and if belt tension is contributing to your bearing loads, get an application-specifc belt tension value and use it.

 

[Tmoose]

If the belt driven shaft is of adequate size we used to make steel sleeves that straddle the worn area, and modify the bearing pedestal to accommodate a larger bearing.

The tradition continues -

https://www.hitekbalancing.com/shaft-sleeve-kit/

https://www.hitekbalancing.com/on-site-shaft-repairs/

 

[Frontier12]

The entire piece of equipment was damaged during unloading. The shaft has the pillow block bearing on one side and a tapered roller assembly that rides in a track on the other.