Shaft runout

[brin]

Is there a standard procedure for establishing shaft runout limits? I have a 4 inch long, .63 inch dia shaft turning at 7400 rpm. The shaft carries a belt sheave and has splines at one end. It is supported by two bearings.

This has become a discussion question and I would like to find out what would be the maximum runout that would be practical on a shaft such as this. I've had opinions from .0005 inch TIR to .002. But it was strongly suggested that a runout of .002 TIR would cause disasterous vibration, or destroy the bearings. However, the shaft and sheave assembly will be balanced as a unit- excessive runout will show up during the balance procedure.

From an analytical approach- I used the manufacturer's allowable misalignment values for the bearings to determine a deflection curve of the shaft, and from there determined a .001 total runout limit (.002 TIR). But I'm not sure if this is an acceptable method.

As for guidelines, I found one reference on transmission shafting that recommended .001 in per foot of shaft length, but another reference recommended .010 in/ft for the same application. There is a SAE standard for splined accessory drives that uses .002 between shaft OD and spline pitch dia.

Any comments or recommendations would be appreciated, thanks.

 

[pdybeck]

Consult the bearing catalogs from the manufacturers to follow their acceptable runout tolerances. SKF usually has some great information in their general catalogue. You can get these catalogues for free usually. The vaules you talk about will be different depending on the type of bearing and the size of bearing. Different types of bearings will accomodate different amounts of mis-alignments. Some types of bearings are designed for this reason, but they tend to come at a price premium. It is not uncommon for something like .001 TIR on the bearing seat to be called out for a ball bearing. Also, don't forget to tolerance the perpendicularity of the shoulders on the bearing seats. It is not uncommon for these to be held to .0004 perpendicular for deep groove ball bearings of 1" ID. It can be good practice to have the centers on the shaft be your datum features. You can callout TIR and perpendiculairty relative to the centers. This is helpful, b/c shafts are usually turned on centers, and also easy for inspection as the shaft can be placed on those centers and rotated to check TIR and perpendicularity with an indicator.

 

[brin]

Thanks pdybeck- I'll check into the shoulder face perpendicularity issue.

Is it standard practice to use the bearing misalignment to determine shaft runout limit?

On the guideline for transmission shafting, do you know if this should read .001 in/ft between supports, or .010 in/ft? I haven't found any other references to corrolate this.

We're considering using shaft centers for the next batch- the present batch measurements were done with the parts supported in a lathe chuck.