You sure your grinder has bearings?

O

Omega Leather Works

Joined
Jun 13, 2007
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Kidding, but I do have a motor question.

I noticed in another thread that the recommended motor size for most 2x72 grinders is 1.5+hp. In fact, one person was recommending 5hp.

As I'm walking around the plant tonight I've been looking at the motors that we use for various tasks. There are dozens of them in use. Most of the motors seem to fall into the 1-1.5hp range. The motors typically run for years (24/7) with no problems, and their lives are *not* easy.

So why are the requirements for grinders so high?
 
I think a 220/240V 2HP motor is plenty. You will have a hard time bogging it down.
 
If you are grinding a wide blade on a flat platen, some sort of rule of thumb is a HP per inch of belt width

Full flat grinds on wide blades, tang tapering, integrals,

It's a high drag operation
If you're pushing hard, you can stall the motor




I started on a full speed grinder with no variagle speed so I have a light touch


but if I'm using the grinder for simple fabrication, I can push hard enough to stall it.

If you're using a wheel, not nearly the same friction loss.



If you are a FT maker, time is money and the higher HP is useful
five seems excessive though
 
most of those motors probably have a gear system to help them out. i have a 110 vac 1.5hp motor and it does not take much to slow it down.
 
chad2 said:
most of those motors probably have a gear system to help them out. i have a 110 vac 1.5hp motor and it does not take much to slow it down.
Click to expand...

Some do, yes, but not many. All are driven off vfd's.

I'm woefully uneducated on the topic of electric motors.

Do rpm's play a big role? From the articles that I've written on electric cars, it seems that the motors have a very flat torque curve (no toque curve?), so does it matter if you run the motor at, say, half speed vrs. full speed?
 
I use a VFD and a 1.5 hp 220 motor on my KMG grinder which has the standard 4 inch drive wheel and it produces about 3600 surface feet per minute I estimate. Yes it can trip the power strip circuit breaker that I have when flattening a blade against the platen but when it does I put on a new belt and use a little less pressure. I have made over 300 knives on the grinder. I will say that if I had a 220 outlet near my grinder then I would have bought a 2 hp motor and some day when I can find no more ways to spend money on this endeavor I will do just that. In my opinion a 2 hp would do just about anything. I saw a youtube video recently of a knife maker with a machine with a huge drive wheel claiming 7500 surface feet per minute and he was grinding hardened steel fast. I believe heat treat should come AFTER grinding. Maybe he is a genius but that is too fast for my style of knife making and I make a pretty decent knife I am told. Larry Lehman
 
I agree with numbers above.

2 hp is just about right for a 2" belt grinder.

1-1/2" hp is OK for smaller blades, but under powered for wider/larger blades.

3 hp is really perfect for a 2x72' grinder.

Variable speed is the only way to go.
 
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