Belt Drive Help

[bearwen]

I am designing a new router and well it will be 4' X 4' and I am going with belt drives. The question I have is how do I calculate the amount of motor torque needed to move the gantry. I figure the gantry will weigh 50 to 70 lbs and you need what about 40 to 60 lbs of cutting force so really not counting the ramp up and down to speed stuff the gantry weight is nothing really as its on bearings so we need 40 to 60 ftlbs of torque to push the bit through the wood. So what is the formula to figure out what size motor I would need to get the 40 to 60 ftlbs of torque at the bit. I have not bought motors for the new machine and dont want to go to big or to little I do have motors from my other machine and wonder if they would be big enough. Please let me know how to calculate this stuff. I assume reduction drive will be needed but want to get the formulas to figure out the max speed I can get with a set amount of cutting force and pulley sizes needed for a set rpm. So please give formulas and keep them simple as possible rough estimate formulas will do.

[ger21]

It depends on how you're driving it, but the force delivered from a drive pulley is equal to the motor torque divided by half of the pitch diameter of the pulley. Keep in mind that you'll want to calculate the force at a given rpm, as a steppers torque drops off as rpm's increase. So, if you need 50 lbs of force at 250ipm, you'll need to know the steppers torque at the rpm it needs to spin to give you that velocity.