Kennametal has one on their site if memory is correct.

The Society of Manufacturing Engineers has done studies over the years and so did Cincinnati Millicron ( out of buisness now ).

There are also a few other sites as well. I have done it manualy by finding the shear area and then finding the generated force. You need to make some assumptions ( like i used the mean average of ultimate tensile / yield / and shear stress for a material ).

HP=FV/33000 where F=# V=ft/min ( spindle) then consider motor efficiency , mechanical reducing into it. Just be practical and conservative if applying the results as there are variables which just can't be calculated and are factored based on testing and practical experience over time.

Additionaly there are programs that will caculate required torque, acceleration required for a given axis based on machine / motor / etc parameters and you can account for the metal cutting forces . Danier Motion or Superior Electric come to mind for a program. They are different for steppers and servos and you really should have a torque curve for the motor.

Above all .........garbage in =garbage out

RICH