Fillet radius of Stepped-down shaft

[dforce]

Hello,

I was wondering if anyone out there knew where I could find good design rules / practises defining the proper radius at the point in a machined shaft where the diameter changes abruptly (such as at a bearing shoulder).

I know it is a function of the larger diameter, D, and the smaller diameter, d, as well as the type of stress the shaft receives (torsion, or bending, or both). I was wondering if there was any set of "rules" for minimum radius, r, based on this D/d ratio to acheive acceptable stress concentration in this area?

Thanks very much

D

 

[rb1957]

the stress concentration of a fillet radius on a stepped shaft is a very typical solution, one source is ...

http://www.fatiguecalculator.com/constamp/index.htm

the design guide-line is to make the stress concentration either as low as you need to meet the fatigue life requirements of your part, or as low as you can reasonably afford.

 

[stanlsimon]

Looking at the situation from the aspect of the lathe operator the minimum inside corner radius would be the smallest radius on the carbide cutter insert that is available.

 

[chief]

You could also look at the equivalent radius on a ball bearing inner race which has to fit snug against the shoulder.

Offshore Engineering&Design

 

[PeterCharles]

All steps on our shafts are specified to have a 3mm fillet radius unless otherwise specified. Sometimes the radii have to be to suit proprietary parts mounted on them.

 

[gearguru]

The largest radius you can use is the best. But as already other people said:
One limitation is the corner radius on the bearing's internal ring. Any bearing catalog has the chart with the recommended radii.
And yes - select the size using the standard insert tip radius. The manufcturing people will appreciate it.