Hello all - I have to eat a bit of crow here. For the last yr or so I've stated pretty flatly that a pulley arrangement is just fine for a 2X72 grinder. About a yr or so ago I built a KMG clone using a 2hp, 3450 RPM 1 ph motor with a pair of 4 step pulleys. That gave me belt speeds around 1200 SFPM, 1700 SFPM, 3400 SFPM, and 4800 SFPM - a good range for the first 3 lower speeds. 4800 SFPM was just too fast for anything and grinder sounded like it was going to "take off", but boy would it make sparks!! Grinder was always a bit noisy but ok. A couple weeks ago I decided to build a new grinder using a 3ph motor with VFD - boy does a direct drive run smoother and quieter!! I'm VERY impressed with now much smoother and quieter. A couple of photos of new grinder (sorry photos are so large, but first time to use photobucket in a LONG time.)
I'd always maintained the cost of a pulley arrangement was a much less cost, but that was "assuming" a motor, shafting, etc were on hand which was the case with my first grinder. All this "on hand" stuff saves a good bit of money. This time I purchased a new motor/VFD setup, and realized the price really isn't much more than pulley setup, IF you have to purchase all the pulley setup parts.
Cost of new grinder was less than $500 total cost.
2hp, 3 ph motor: $127 shipped. (TEFC motor)
3 hp VFD drive: $116 shipped
Aluminum: $150 shipped.
Platen assembly: $30 (4 skateboard wheels)
4" drive pulley: on hand (metal to make $20?)
I ordered aluminum from a place with most parts cut to length, so all I had to do was drill holes and cut a few pieces. Having access to a lathe and milling machine sure helps. The motor mount plate has to be turned on a lathe for an easy fit.
The VFD is an open type, NOT a NEMA 4X to prevent dust from entering. The green filter I fitted around vent holes in VFD can be seen - will this prevent all dust? Doubt it very much, but for my causal use of grinder should be ok. I have a NEMA 4X box I can mount VFD in, but then holes to circulate air would be required with the same filter setup. "IF" I were grinding every day, then I'd spend the extra bucks for a NEMA 4X rated drive. I'll use this one until it fails, then depending on how long it lasts. Additional cost of a NEMA 4X VFD would only had a couple hundred to cost.
The small box just below left corner of top is a box for ON/OFF of 220VAC, a RUN/STOP switch, and a pot for controlling speed. The VFD display can be seen and displays SFPM normally, but can scroll thru for freq, temperature, and amps. The SFPM is the RPM function, but with a factor to be SFPM rather than RPM. If I turn the 4" drive wheel to 3.7", then RPM
I've found 3" skateboard wheels (72a Hardness) to work good for the platen wheels. Again, I take back all I've said about pulley arrangements for grinders - even with hinged motor base so belts can be changed in seconds, the direct drive is so much nicer!
The plywood and metal for stand were on-hand so that cost isn't factored in to the grinder cost. Note the hinged plywood - this allows grinder to be flipped to horizontal easy. I'm still learning about use of horizontal position, so have to complete support for that position. My tool rest is designed so it will work for horizontal or vertical position.
Ken H>
I'd always maintained the cost of a pulley arrangement was a much less cost, but that was "assuming" a motor, shafting, etc were on hand which was the case with my first grinder. All this "on hand" stuff saves a good bit of money. This time I purchased a new motor/VFD setup, and realized the price really isn't much more than pulley setup, IF you have to purchase all the pulley setup parts.
Cost of new grinder was less than $500 total cost.
2hp, 3 ph motor: $127 shipped. (TEFC motor)
3 hp VFD drive: $116 shipped
Aluminum: $150 shipped.
Platen assembly: $30 (4 skateboard wheels)
4" drive pulley: on hand (metal to make $20?)
I ordered aluminum from a place with most parts cut to length, so all I had to do was drill holes and cut a few pieces. Having access to a lathe and milling machine sure helps. The motor mount plate has to be turned on a lathe for an easy fit.
The VFD is an open type, NOT a NEMA 4X to prevent dust from entering. The green filter I fitted around vent holes in VFD can be seen - will this prevent all dust? Doubt it very much, but for my causal use of grinder should be ok. I have a NEMA 4X box I can mount VFD in, but then holes to circulate air would be required with the same filter setup. "IF" I were grinding every day, then I'd spend the extra bucks for a NEMA 4X rated drive. I'll use this one until it fails, then depending on how long it lasts. Additional cost of a NEMA 4X VFD would only had a couple hundred to cost.
The small box just below left corner of top is a box for ON/OFF of 220VAC, a RUN/STOP switch, and a pot for controlling speed. The VFD display can be seen and displays SFPM normally, but can scroll thru for freq, temperature, and amps. The SFPM is the RPM function, but with a factor to be SFPM rather than RPM. If I turn the 4" drive wheel to 3.7", then RPM
I've found 3" skateboard wheels (72a Hardness) to work good for the platen wheels. Again, I take back all I've said about pulley arrangements for grinders - even with hinged motor base so belts can be changed in seconds, the direct drive is so much nicer!
The plywood and metal for stand were on-hand so that cost isn't factored in to the grinder cost. Note the hinged plywood - this allows grinder to be flipped to horizontal easy. I'm still learning about use of horizontal position, so have to complete support for that position. My tool rest is designed so it will work for horizontal or vertical position.
Ken H>
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