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Originally Posted by sanddrag
Will the oversize (1/8") keyway in the picture below be okay to make? I want to go oversize because I'm worried that a 3/32 key is too small for where this gear is in our box. It needs to be able to handle some torque, maybe somewhere around 13 Newton-meters.
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Originally Posted by Max Lobovsky
19 Nm = 9.6 ft-lb
9.6 * 12 = 115 in-lb
115 / ((3/8)/2) = 614 lb of force shearing the key
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You need one more piece of information: Length of the gear and hub. This gear has a face width of .50 and hub of .46, for a total of .96 inches.
You will have an overall width of either .125 or .09375.
Steel has a tensile strength of 40,000 lbs / inē, and a pure shear strength, (using Mohr's circle), of roughly half that. This is conservative, because most keys will be of a higher grade material with a higher strength.
You also have 614 lbs of shear, correctly calculated earlier.
Area = .96 * .09375 = .09 inē
614 lbs / .09 inē = 6,822 lbs / inē
Giving you a factor of safety around 2.93 with your 3/32" keyway.
If your feel pretty comfortable (or even within 100% of) the expected torque, I would say that your 3/32 key should be acceptable.
Matt