which steel to use for an axle and tips on splining

I wouldn't bother. You won't have any trouble with this application using the steel as is.

Karl

I do not know your application but you might consider two sprockets, one mounted on either end of the shaft, coupled with double roller chain.This would require just two keyways to be machined. This setup also allows for some misalignment. Steve

Really have to know more about the specific application. That shaft can easily handle 200 horsepower. Or it might twist with 1/4 horse. All depends on the speed.

John Martin

Here are the equations governing your shaft:

HP = T * RPM / 63024 (where T is in in-lb)

Tau = K * T * c / J (T is torque, found above. Tau is the max shear stress due to T. c is the max radius (D/2), and J is Pi*c^4 / 2 for a solid shaft. K is a stress concentration factor and varies from ~1.1 for a shaft that gently radiuses into a larger dia. spline, to 2, 3+ for steps, keyways, etc. Another K should also account for fatigue losses, if this is a high cycle app. Roughly speaking you can throw in another K of 2 for infinite life.)

Tau_allowable = .58 * Yield_Strength / Safety_Factor

Yield Strength depends a lot on the heat treatment, as you probably know.

Simplifying: T = HP * 63024 / RPM Tau = 16 * K * T / ( Pi * D^3) = .58 * YS / SF

Combining and solving for YS, I get (check this)... YS = 553,000 * K * FS * HP / (D^3 * RPM) (where D is in inches and YS is in psi)

E.g., if K=3 (some fatigue plus stress conc.), FS=2, HP=4.0, D=.5, RPM=1600 YS = 66,360psi

So, IF those RPM and HP numbers are the same as yours, D is .5 or greater, and your splines don't have severe stress risers, then you need a material with that YS, or greater. 4140-Normalized is around

Some cautions: Motors can give ~1.5x their full load torque. Inertia or braking torques can be many times the running torque. Strength is very sensitive to D ( 1 / D^3). If shaft failure could cause human injury, FS=2 may not be enough. Keyways have big stress risers. If your spline od is the same as the shaft od, you need to be working with the diameter of the spline root, or use a larger K.

David