Grinder Speed

B

Brad Lilly

Moderator and Awards Boss
A long while ago I started a no weld EEFR grinder and I'm finally wrapping it up. I bought a 4" drive wheel and a 2hp 3 phase motor, my VFD is 60Hz. Everything works well but it is slow. When grinding I throw very little sparks. What is everybody using for drive wheel sizes? I think my motor is turning 1725 with a 4" diameter wheel that would be 1805 feet per minute (By redneck figuring) I'm thinking I should have tried to fit a 6" drive wheel on it (2932.5 Feet per minute).
 
Guess this is direct drive like the EERF brad ?

3600 RPM motor would be best for direct drive. What type VFD are you running. Wayne Coe set them to run 2x speed on a KBAC I believe which would work for you.

I'm turning 3600 RPM at the driveshaft with a 4" drive wheel and I'm considering going to a 6" drive wheel also :)

-Josh
 
Exactly my thoughts Brad.

I think just doing a 6" drive wheel would be a waste of your resources. My opinion only of course.
 
That's not good. I do have a guy who would make me a custom wheel, I could get away with 8" maybe. I will have to do a bunch of checking to make sure I have the clearance. That should give me 3611 feet per min, by the same math yours would be running 3768 with a 4" wheel. (by redneck figuring. I got to get this figured out soon, I don't have enough fingers and toes)

I was going to save money by building my grinder.
 
What VFD are you running? I have a 2hp 3PH 1750 running through a KBAC 27. There is a switch that allows the motor to run at double speed. If you have a KBAC 27 I think I can show you which switch.
 
I think you may want to rethink the 8" drive wheel , by going to a larger drive wheel you will diminish your toque output and may find that you stall the motor. I run a 2 HP 3ph 220 v motor with a direct drive 4" wheel and bounce sparks all over .If you look you should be able to find a 3600 rpm motor at a reasonable cost.
 
Well I got a hold of my electrical guy and he told me I should be able to over speed my motor by changing the max Hz from 60 to 80. The VFD is a toshiba VF-S15.
 
Make sure that you wired to the motor for 240v and not 480v. I had one customer that did that and complained that his motor ran to slow. He then re-wired it and was cookin'. The problem that you will find with the VFD is that it is not NEMA 4X rated and will suck metal dust into the VFD thereby shorting it out. Either get a NEMA 4x VFD (KBAC) or put that one in an enclosure, then you will have to allow for a fan, holes and filters to keep the dust out.

Make sure you have a good sharp belt on the grinder. A worn out belt won't throw many sparks. Just an after thought.
 
The last few grinders I have made I switched to 3600rpm motor from 1750. I like the increased speed and don't find the slight torque reduction is a good trade.
 
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