Shaft Design (Machinery Handbook)

[Josh2008]

I heard somebody mention there is a "rule of thumb" for shaft turndown ratios mentioned in the machinery handbook. I cannot find the reference. Would somebody know of such a thing?

Ex. Should not turndown a shaft more than 25% of its diameter, meaning a 4" diameter shaft should not reduce less than 3" in diameter.

Please advise.

 

[Cockroach]

Rework of shafts would require specific analysis of the load case in order to determine what is the best way forward. How could you say 25% is a reasonable number to cover all cases. Would this constitute "a rule of thumb"?

You need to look at the situation on a case by case basis. I can have a four inch diameter shaft and have it loaded to 5% less than maximum allowable bending. So reducing it to 3.0 inches would certainly lead to catastrophic failure.

On the other hand, I could have a four inch shaft with one pound sitting an inch to the inside of a support. Reducing the shaft to 1/2 inch diameter would not be an issue. Since this is a much higher reduction than 25%, would this constitute "a rule of thumb"?

Case-by-case basis, brother. Need to push the pencil.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada