Thread: Horsepower, Torque, Gears and Belt drives

1. Horsepower, Torque, Gears and Belt drives

I have seen lots of posts in this Forum that use Horsepower and Torque interchangeably. Although related, they are not the same. Horsepower is a measure of work and Torque is a force. They are related by the simple formula: Torque = Horsepower/RPM*5250. Conversely HP = Torque/5250 * RPM
Using the common upgrade motor (2HP @3450) Torque = 2/3450*5250 = 3.04 ft lbs. Now lets slow it down with our VFD to 1750 RPM. The VFD says it will keep constant torque. HP = 3/5250*1750 = 1 HP !!!. This is the same as the stock motor. We have gained top speed –a good thing—but no change in Horsepower at half speed. Compare this to slowing the spindle with a 2:1 gear. Our horsepower would remain at 2 and our Torque would double. The force (torque) doubles but the work (HP) remains the same.
Gears are a great solution because machines need ever increasing Torque at lower speeds. We need constant Horsepower. When you plug into G-Wizard (great product) that you want to drill a 1” hole in some 4130 steel plate, it will tell you that you need 0.6 HP at 320 RPM. Your 2HP 3450 RPM motor needs at least a 3:1 gear—better would be 5:1. This is why a VariDrive Bridgeport has a 9:1 backgear and a belt drive for an astonishing 160 ft/lbs of Tq at 60 RPM from a 1.5 HP motor.
The bottom line is keep your gears. They are a very good thing

2. Originally Posted by Lotusjohn
I have seen lots of posts in this Forum that use Horsepower and Torque interchangeably. Although related, they are not the same. Horsepower is a measure of work and Torque is a force. They are related by the simple formula: Torque = Horsepower/RPM*5250. Conversely HP = Torque/5250 * RPM
Using the common upgrade motor (2HP @3450) Torque = 2/3450*5250 = 3.04 ft lbs. Now lets slow it down with our VFD to 1750 RPM. The VFD says it will keep constant torque. HP = 3/5250*1750 = 1 HP !!!. This is the same as the stock motor. We have gained top speed –a good thing—but no change in Horsepower at half speed. Compare this to slowing the spindle with a 2:1 gear. Our horsepower would remain at 2 and our Torque would double. The force (torque) doubles but the work (HP) remains the same.
Gears are a great solution because machines need ever increasing Torque at lower speeds. We need constant Horsepower. When you plug into G-Wizard (great product) that you want to drill a 1” hole in some 4130 steel plate, it will tell you that you need 0.6 HP at 320 RPM. Your 2HP 3450 RPM motor needs at least a 3:1 gear—better would be 5:1. This is why a VariDrive Bridgeport has a 9:1 backgear and a belt drive for an astonishing 160 ft/lbs of Tq at 60 RPM from a 1.5 HP motor.
The bottom line is keep your gears. They are a very good thing
The way you've presented the equations, they're easily misinterpreted. To clarify, it should be:

Horsepower = (Torque * RPM) / 5250

Torque = (Horsepower * 5250) / RPM

Regards,
Ray L.

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