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repurposed 1/2 HP motor as a grinder?

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Forum topic by luthierwnc posted 06-05-2016 06:59 PM 268 views 0 times favorited 3 replies Add to Favorites Watch
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luthierwnc

115 posts in 1238 days


06-05-2016 06:59 PM

Hi All,

I have a spare motor that I took off my 1957 Rockwell drill press when I went to a 3-phase VFD. It is the original motor and is rated at 1/2 HP at 1750 RPM. I disassembled and cleaned it and replaced the main bearings. The motor has usable shafts on both ends and I already have the arbor attachments. It runs very quietly (always did) and I think it might make a good slow-speed grinder. I already have a high-speed one but the slower version might be handy for tempered steel.

At any rate, I really don’t know how to assess the power. Horsepower standards seem to vary among manufacturers for more-or-less the same motor. I’m guessing a US-made model from 1957 is probably close to spec.

If it can handle it, I’d like to put a medium-grit 1” X 8” wheel on one side and a buffing wheel on the other.

If anyone has thoughts on the capacity, I’d love to hear them. Thanks, sh


3 replies so far

View CyberDyneSystems's profile

CyberDyneSystems

220 posts in 1650 days


#1 posted 06-05-2016 07:42 PM

1720 RPM is great for both buffing and low speed grinding. 1/2HP should be plenty for 6” or 8” wheels.

The problem you might run into is getting those arbor shafts to be exactly straight/centered.
I’ve never found an add on shaft that will do that job. (let me know if anyone reading this has a source!)

On a buffer, this is not a huge problem, with an actual grinding wheel installed, you could be in for some serious vibration. You just can;t be that far off center with a hard wheel. Particularly a large one.

I’ve got an old dual speed motor (1720/3540) that I use almost always @ 1720 with a buffer on one side, and a wire wheel on the other (wire wheel is particularly forgiving of the slightly off center shaft)

Lastly, and MOST IMPORTANT if you do get well centered arbors, and do install a grinding wheel, either build a sufficient guard to protect from catastrophic wheel explosions, or use CBN wheels. Another benefit of buffers and wire wheels on such a set up, guards or not required (just always use eye protection, particularly with a wire wheel)

-- Without the wood, it's just working

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luthierwnc

115 posts in 1238 days


#2 posted 06-05-2016 08:05 PM

Thanks CyberDyneSystems, You’re right. I hadn’t really considered run-out on the arbors.

With that in mind, maybe my best bet is to take the wire-wheel off the high-speed grinder and put it on the drill press motor along with a buffing wheel. That saves me having to build tool-rests and guards. Reduced speed might also cut down on little steel wires sticking in my forearm.

I’ve got two other grinders. One is a Grizzly 10” wet stone (which is really cool) and the other is a flat water wheel which I got new, cheap 25 years ago and still works. It has some similarities to the Makita wet wheel. Great for lapping the backs of blades. It has a slow-speed vertical wheel too and I keep a Kraytex disc there for shining metal.

Thanks for the heads-up, sh

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CyberDyneSystems

220 posts in 1650 days


#3 posted 06-05-2016 08:48 PM

Wire wheel at 1720 rpm is really great! Slipping and getting a finger in there is a lot less painful too.

I had it up to 3540 earlier this week for a particularly tough job, and literally as I was explaining to my daughter why one always wears eye protection when using a wire wheel, a wire came loose and stuck into my forehead about 2 inches from my safety glasses/eye! Talk about a live demonstration! :) that never happens with that kind of sticking force @ 1720rpm.

-- Without the wood, it's just working

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