TUFNOL Technical information

TUFNOL GEARS – Calculating Keyway Stresses

KEYING.

This is the preferred method of fixing a TUFNOL gear to the shaft and in the majority of cases, a keyway cut into a plain bore is adequate. Parallel keys are strongly recommended. Tapered keys, if used, may possibly be overdriven and it is advisable to fit steel shrouds or bushes to take the wedging action of the key. Bushes, shrouds or plates should also be used to reinforce the keyway when the maximum keyway stress will  be exceeded. Grub screw fixing is not usually recommended unless a metal bush or collar is fitted to take the screw. Force fitted, knurled or splined shafts require careful design but can be very successful in the right situation.

KEYWAY STRESSES

For plain gears the keyway stress should not exceed 21 MPa (3000 lbf/in2). This stress may be calculated from the following equations:

SI Units

S' =     1000 P'

             L' x H' x V'

where S'  stress on key, in MPa

P' = power transmitted, in kW

L' = length of keyway, in mm

H' = height of keyway, in mm

V' = peripheral speed of shaft, in m/s

Imperial Units

      S' =    33 000 

              L x H x V

where S'  stress on keyway, in lbf/in2

P = power transmitted, in horsepower

L = length of keyway, in inches

H = height of keyway, in inches

V= peripheral of speed of shaft, in ft/min

These equations relate only to the stress caused by transmitting the working torque. Stresses due to high interference fits in the keyway should be kept to an absolute minimum but, if particularly high, intereference must be accommodated, the use of steel shrouds should be considered.