Grinder motor

J

Jason Fry

Joined
Jun 5, 2008
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I snagged a 3/4 HP two speed motor off of Craigslist for $10. I think the speeds were 1750 and 1170 RPM. Had a wierd looking four prong plug. Several questions. One, is 3/4 enough HP for a Goddardesque grinder? Two, If it's not, what applications is it good for? Three, how would I go about wiring it, since I don't happen to have any wierd four prong outlets? I think a 3 position switch with high, low, and off should work, right?
Thanks,
Jason
 
jkf96a said:
I snagged a 3/4 HP two speed motor off of Craigslist for $10. I think the speeds were 1750 and 1170 RPM. Had a wierd looking four prong plug. Several questions. One, is 3/4 enough HP for a Goddardesque grinder? Two, If it's not, what applications is it good for? Three, how would I go about wiring it, since I don't happen to have any wierd four prong outlets? I think a 3 position switch with high, low, and off should work, right?
Thanks,
Jason
Click to expand...

1. I'm no expert but a 4 prong plug make me think it's a 220 motor. 3/4 can be used for a belt grinder but you may be able to stall it out, it'd be wicked as a 9" disk grinder though.

2. You can probably go to a GOOD hardware store and find that plug and get someone to help you wire it up.

3. Not sure if it works as "high, low, off" usually the way you wire it up determines the motor speed. (never mind, I just read that it was a 2 speed motor.)

$10, it's worth it if you can figure stuff out.
 
i like 3/4 hp for a disc grinder, i had one but had to switch out motors, for a smaller one cause it needs some wires replaced.

i think my buffer might be 3/4 or maybe half, either way, for a buffer, id go with the slower speed, and maybe even slow down a bit more with pulleys.

and for the goddard grinder, 3/4hp should be a sufficient place to start, could always speed it up with pulleys, and make it a vari speed with step pulleys.

just my two cents.

andrew
 
I just looked at it again... it is 110 V, with a small wiring diagram on the plate showing three wires plus a ground... one wire for high, one for low, plus a neutral. The motor is from an evaporative cooler, where the power is run to a switch inside the house, if that helps the understanding any.
 
For 10 bucks it will spin a belt, but you will be able to bog it down. That can get you by till you find a 2hp motor then it will take quite a bit to bog that down. Then turn the 3/4 into a disc sander. You will also get a feel for how fast you like to spin belts, and you can refine what you are looking for in a stronger motor.
 
Anyone have a good supplier source (new is fine) for a variable speed motor for a Coote grinder?
 
gixxer,

Wow, that's a great price for a 3 hp! You said you have a few of those motors? How do they hold up? Also, would these motors be suitable to hook up to a VFD?

Also, what motor would be better for a grinder drive...1800rpm or 3600rpm?

--nathan
 
I have not hooked up the 2hp yet, but the 3/4 sees regualr duty as a disc sander. They are 3 phase, hooked up to a vfd. 1800 or 3600? That all depends on how fast you want to spin belts. I did a feeler post to get folks opinion about their grinder and if they wanted faster or slower. Those that posted wanted faster. The common consensus was that with the VFD you can always slow down, so rig it to go faster. Gimme a sec to find the formula for SFPM, I forgot already what I am going to get. Something like 5600 SFPM maxed out. I am rigging my new grinder with the 2hp 3600 RPM motor and a 6" wheel direct drive on VFD.

A 4" wheel at 1800 gets 1884 SFPM, 3600 is 3768
5" at 1800 is 2355 SFPM, 3600 is 4710
6" at 1800 is 2826 SFPM, 3600 is 5652
 
www.factorymation.com
I use the FM50 VFD's. I currently own a Nema 4 enclosure model for the disc sander, but I am getting the IP20 enclosure (it's not as expensive) and making my own filtered box with external controls. Remember kids, you NEED an enclosure with filtered vents on it if you are not using a NEMA 4. I got the idea from another thread where the guy made a vented box with plain jane air filters from the auto parts store. I believe it is in the middle of a thread entitled 110/220? maybe. Those that can search can look up my posts and backtrack to that thread.
 
jkf96a said:
I just looked at it again... it is 110 V, with a small wiring diagram on the plate showing three wires plus a ground... one wire for high, one for low, plus a neutral. The motor is from an evaporative cooler, where the power is run to a switch inside the house, if that helps the understanding any.
Click to expand...

you can wire it thru a 3 position toggle switch , Hi,off,low is the way they work . Make sure the toggle switch is rated for the amp draw , at least 15 amps . Just follow the wire color code and wiring diagram .
 
An easy way to do it is to take the plate off the motor covering the wires. One should be attached to high, one to low. If you just want one speed, remove the wire for the speed you don't want, and just wire on a regular 3 prong plug ignoring whatever color you didn't hook up. I was using a 1hp spa motor that had one of these plugs for a while. I just got a 2hp motor and what a difference. I wish now that I never used that underpowered motor because it only made me quit looking for a real motor for a long time. If you use it, keep looking for a 2hp motor because you will suddenly realize what a grinder is actually capable of.

-Mike

By the way, I think a 3 way toggle switch is a much better idea.
 
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