I may also put an all in one high speed spindle on that mill project. 3. 2.5HP DC treadmill motor. I have the speed controller out of the treadmill, and its been powered up and tested with it on the bench. These have often been used for belt grinder projects. I have also been thinking about using it for one of the mini lathes when I finish ...
There is a lot more control in the lower speeds. Also you brush a finger or nuckle on a 36gr belt going 10,000 fps and it39;s not good. I think if you built one good grinder with a VFD and 3hp 3ph motor with a max speed of around 4000 5000fps you will really like it.
The speed of a motor is important but can be compensated for by using the VFD to increase the motor speed or by using a larger diameter drive wheel to make up for lack of speed. Pulley, shaft and belt arrangements can also be used to compensate for motor speed. However, not all grinder designs will accept these extra moving parts.
If the motor on your bench grinder is under 1HP you should be able to control the speed with a router speed control. My experience with this kind of set up,however, is that when the speed is lowered, it loses its steady rhythm and jerks between 90 and 110 RPM Fitting a Belt Pulley
More than one belt grinder has been built without a speed control. Keep in mind you can also use pulleys to get a few fixed speed options. I would recommend starting simple and get a basic fixed speed belt grinder working. The designs are tried and true and reasonable easy to build.
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My preference would be a DC motor rated to around 200 250 VDC. I could then build a PWM circuit to control the speed and run it from the numerous 240 VAC outlets I put in my shop. From what I39;ve read and my own experience as a machinist, I will design this grinder to have belt speeds of between 15 and 30 m/s.
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The rule of thumb for belt grinder motor power in industry is 1 HP per inch of belt width . Standard industrial motors tend to be designed for a maximum continuous mechanical speed of 3600 RPM to cover 2 pole motors running on 60 Hz mains in those parts of the world that use it.