Slow 1/2 HP Motor Good for Grinder?

[Bob Lyon]

I found a 1/2 hp, 875 rpm motor that ran a large fan. Since it has 1/2 hp at 875, does that mean the effective power will be greater after using pulleys to increase the speed transmitted to the grinding belt? There should be some basic high school physics here that I've forgotten as the hair goes grey.
Thanks,
Bob

 

[Bruce Evans]

I have used a 1/2 hp before but it didnt have the power when it was dogged on a little you need at least a 1 hp but a 2 hp would do betterthen you can slow it down and keep your torque.Hope this helps.....Bruce

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[TJ Smith]

it looks like the rpm was dropped to get the horsepower. If you geared up to increase belt speed your hp would go down.I had a 1\2 on my old homemade grinder but it was 1725 rpm and I could stop the motor if I pushed real hard on the knife blank.I went to a 3\4 horse at 3450 and geared in down to 1725 and you couldn't stop it.
Take Care
TJ Smith

[This message has been edited by TJ Smith (edited 06-25-2000).]

 

[tom mayo]

you can buy low rpm motors at any horsepower, but they are expensive....the lowest you can get without paying too much is an 1125rpm....you can also get motors with a 1/2 power switch.....one horse 1725 and 1/2 horse 850 or whatever it is....I have researched this extensively....the best bet...but not the cheapest....is a 1.5 horse dc motor and controller for around $600.. this is what you want, what you are going to end up with...and what you should get from the get go.....ask any accomplished knifemaker and they will tell you the same thing. I'm not saying you have to...just its a whole lot easier this way.

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[magnum .44]

tom, i got a leeson 1.5hp dc variable speed motor, with controls from woodcraft for $530, plus shipping.

 

[Matt Shade]

I remember reading the definiton of horsepower as the amount of force needed to lift 100lbs at a rate of 1 foot per second (not word for word) Anyhow if the motor is putting out 1/2 horsepower at a low RPM its got more torque than a fast motor putting out 1/2 horsepower. Thats because horsepower is a rating of energy put out in a specific time frame, the faster the motor the more energy it puts out in that time frame.
I think your motor would be fine for grinding with. My grinder (4x36 belt sander) is only 1/3HP and it does fine. You can't hog off a lot of metal like you can with a big grinder, but I've never stoppped the belt before. Unless your planing on doing lots of heavy grinding, like all these guys that take orders and sell knives, your motor should be fine. It ought to put out enough torque to keep from getting bogged down much, unbless you plan on really leaning into the belt.

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