Interference fits for Gears on Knurled shafts

[mclearg]

Does anyone know of any standards I could source for the required interference/knurl fit for transmitting a specified torque through a gear/shaft assembly?

 

[israelkk]

For a press fit design:

Calculate the pressure created in the interference fit, multiply by the surface area of the fitted area, then multiply by the radius of the shaft and then by the friction coefficient to get the torque.

To be on the safe side assume friction coefficient of say 0.2 (if the area is dry or 0.1 if wet). The resulted torque should be few times larger then the designed transmitted torque.

 

[mclearg]

Thanks for your prompt reply israelkk. The specific problem I've got involves a knurled shaft and a brass gear. I know the torque it has to transmit. This assembly is bought from a Chinese company and we are having to specify to them what we want. Unfortunately I can't get away with telling them the torque that I want! I need to specify the knurl (I've went for a 'Fine Straight Knurl' approx. 0.64mm pitch), the shaft (after knurling) tol. Ø2.6 - Ø2.58 (Ø2.5 Nom), and the Internal Gear Ø of 2.5 +0.1/-0.0.
What I could really do with is a standard or something for knurled fits and the torque transfering capabilites thereof, any ideas?

 

[israelkk]

I assume you mean the internal gear is 2.5+0.01/-0.0 otherwise in case the the tplerance is 0.1 then the internal gear may have a hole of 2.6 which will go freely ove the shaft. If the I am right then whayt I think is that you have to count the number of knurls and their width at the misddle of the knurls height and calculate the shearing strength in the middle hight of the shaft knurls.