Calculate Effective Speed And Power Range For Gear Ratio

native34

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Would anyone on here be able to help me understand how to figure out the right size and gear ratio to make the pulleys for my spindle belt drive conversion? I would like a speed range from 100-6000 rpm. I'm using a vfd and a 3HP motor. What I don't understand is how to determine how fast/slow I can spin the spindle with this setup and have enough power to cut steel and aluminum without stalling the spindle.
 
Given the information that you provided I am going to assume that you are asking about a milling machine, and that the machine has back gear or a low speed gear range. A Bridgeport type machine has a 7.5:1 reduction in low speed. Baldor 1800 RPM nominal mill motors have a max rated speed of 6000 RPM, and maybe the Asian motors will spin that fast also. So we will work from those assumptions.

It is common to use a 1:1 motor pulley to spindle pulley ratio in this setup, but you will want a VFD with Sensorless Vector Control to get reasonable torque control over the full speed range. Then there is the issue of motor cooling when operating the motor at lower speeds. An auxiliary cooling fan is mandatory.

This setup will give you a speed range from virtually 0 to 6000 RPM with plenty of power to do anything you need to do. If you need higher speeds an auxiliary spindle would be the way to go, like a router motor or various high speed spindles available and attached to your quill.

If you need more information we'll be happy to help you out.:)
 
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