DIY Disc Grinder

Mike Jones

Google Master
I have been wanting a disc grinder for some time now. As much as I wish I could have a Beaumont Metal Works variable speed grinder, the price was way out of my budget. I had seen others use a treamill motor/controller from surplus center and a Beaumont Metal Works disc, but surplus center no longer sells those motors, and I don't really have $75 to spend on a disc. Next option: Check Craigslist for a used treadmill (old style with knob/slide speed control is best). I came across one for $25, that I worked into my schedule where I won't use any excess gas to pick up. So now the question is: Where do I find a disc? I had thought about this for a while, then finally decided that a baltic birch (Russian Birch) plywood wheel would be cheap and easy to make.

So here is my progress of this disc grinder.

I started out with 1/4" baltic birch plywood (already had it) and glued 3 10.5x10.5 pieces together to make 3/4" plywood.

To get the treadmill motor, carefully mark all wires on the control board before unplugging them. Remove the dial speed control, control board, motor, and there may be a voltage stabilizer thingy that is not on the board. If you do not know what the wires are, do not attempt this on your own! I had an electrical engineer help me! If your motor only has two wires going to it, you can switch the two inputs to reverse the rotation.
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To remove the flywheel, I took some penetrating oil, let it set in for a few minutes, then removed the coiled part of the motor (with the shaft) and stuck it in the vise with some leather protection. Then I used a breaker wrench to get enough force to get the rusted threads loose.
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I decided to use the treadmill flywheel on the shaft backwards (for a flat surface and better clearance) to hold the plywood onto the motor shaft. I drilled 4 holes about 90 degrees apart.
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I found the center of my plywood and marked it. Then I put the flywheel on the center and drilled the 4 holes into the plywood, dropping a bolt into the hole to keep it alligned. I also marked the plywood with a small hole, at the hole where the flywheel already had one (to always keep it aligned. Both holes together)
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Countersink the plywood holes so the bolts heads rest flush or just under. Put the bolts through and screw the nut on the other side of the flywheel. Cut the bolts to the length needed.
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(The bit accidentally caught the plywood and it rode up the bit, ruining the hole, so I had to fill it with epoxy and try again, rotating it to fresh wood)

I made this jig to drill a hole perfectly in the center of both the pulley section of the flywheel and the threaded shaft.
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Drilling...
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The hole is almost perfect!!!
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Stick a grade 8 bolt through the pulley and threaded shaft, securing with a lock nut.
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I built this fixture to work with my band saw to cut a nearly perfect circle. I measured it to cut a 9" circle out of the plywood. Just slide the fixture into the guide, then rotate the wood being cut.
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So now you have the disc shape cut.
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Put the disc on the grinder, use sandpaper with a hard backing on the edge to make it more round, and to true the face.
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Put a few coats of Danish Oil onto the disc to help stabilize it from any warping.

Now you have a disc grinder! You may wish to put a thin rubber sheet on the disc to soften the surface slightly. I am currently using a cheap spray adhesive that can be used as a readjustable adhesive.
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Total, my costs were:
Treadmill: $25
1/4" Baltic Birch: $14
(4) 1/4-20 Stove Bolts, 1/4-20 Grade 8 bolt, and 5 lock nuts: $2
Spray Adhesive: $5
Rubber sheet (Just ordered mine, so it hasn't arrived yet): $6
Scrap lumber (for a stand): Free
Which adds up to about $52.

$52 for a useable disc grinder. Of course it's not perfect, but when a Beaumont Metal Works disc alone costs $75, I personally will take the $52 one.
 

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awsome...Jonesy, the ultimate spend thrift.

I have a few of those rubber sheets we talked about but I will be getting more. I have been using mine for a couple months and they work well. I'll be getting them listed shortly.
 
That's very cool Mike. Love the redneck engineering! A man after my own heart.

I have a tread mill motor saved that looks just like that one. Problem is, the controller was shot. That's why I scrapped it. I keep hoping I'll run into someone that can tell me how to hook up a transformer and potentiometer to it. LOL
 
That's very cool Mike. Love the redneck engineering! A man after my own heart.

I have a tread mill motor saved that looks just like that one. Problem is, the controller was shot. That's why I scrapped it. I keep hoping I'll run into someone that can tell me how to hook up a transformer and potentiometer to it. LOL
Ebay has a lot of MC-## controllers that you might be able to get to work fairly easily.


Kelly, I will be building a stand for it soon, along with a tool rest table thing.
 
Way to go Mike !

Necessity is indeed the mother of invention !

As long as your disk spins true and has a flat surface then it'll produce the same results as a $900 VSR disk grinder professionally made.

I can't wait for the Mike Jones build a Milling Machine Tutorial !

-Josh
 
Way to go Mike !

Necessity is indeed the mother of invention !

As long as your disk spins true and has a flat surface then it'll produce the same results as a $900 VSR disk grinder professionally made.

I can't wait for the Mike Jones build a Milling Machine Tutorial !

-Josh

It is not 100% true, but the very slight wobble (which is not really an issue right now) will be even lessened once the rubber gets here.

I've actually been thinking of a milling machine... Still stuck in my head though ;)
 
Thanks Mike,

That's a good idea. I looked for the exact old controller for my motor on feeBay, but I guess it won't matter as long as it's the right voltage. Dought!!!!

Sometimes the obvious is just to obvious. LOL
 
Nice job Mike. You didn't waste any time getting that treadmill and building your disc grinder after talking to me on Sunday.2thumbs
 
Thanks Mike,

That's a good idea. I looked for the exact old controller for my motor on feeBay, but I guess it won't matter as long as it's the right voltage. Dought!!!!

Sometimes the obvious is just to obvious. LOL

Glad I could help!

Nice job Mike. You didn't waste any time getting that treadmill and building your disc grinder after talking to me on Sunday.2thumbs

Picked up the treadmill on Sunday, went through the concepts on Monday. Tuesday I drilled everything, Wednesday I put it all together. Today I'm doing the stand, since school is cancelled cause of freezing rain.

Maybe this weekend I can work on a knife! :)
 
I just wanted to mention now that it is coming close to the best time to find treadmills. Spring cleaning can be soon, and people may post old treadmills on craigslist or in garage sales for not much money. If the motor runs and can be controlled (preferably with a knob or slide) then it should work just fine.
 
Nice job Mike....Very creative and well done. Treadmills are only for hanging clothes on anyways, altho my dog does like to run on ours when its 50 below. Of course I have to stand there with treats and give her some every few minutes......:D

Larry
 
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