Instructables

Portable Bench Grinder Using Old Furnace Motor

Picture of Portable Bench Grinder Using Old Furnace Motor
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Have you ever had to work away from your shop, but still need a grinder.  I have, so here is the solution I came up with.  I had an old furnace motor and an arbor.  Very handy to have and simple to make.

Materials List:

1 - Piece of 3/4" plywood, cut to your dimensions
1 - Arbor (available at most hardware or tool stores)
1 - Pulley
1 - Fan belt
1 - Extension Cord
1- Electrical Box with switch and switch plate
2 - Grinding wheels 
Some mounting hardware (screws or nuts and bolts)

Instructions:

Cut the piece of 3/4" plywood to your dimensions (mine is 13" X 22").  You can leave it raw or paint it.  Now layout where you want to mount the furnace motor and arbor and mark the mounting holes.  The position of the motor and arbor will depend on the length of the fan belt you choose.  To mount these two items I would recommend sturdy wood screws or T-nuts and bolts.

Mount your pulley on the shaft of the furnace motor making sure it is the same width as the pulley that is on the arbor.  The pulley on the arbor is in the centre of the arbor, which means you will have to take the shaft off of the arbor to get the fan belt on the pulley.  Make sure when mounting your motor and arbor with the fan belt attached that there is sufficient tension on the fan belt.  It doesn't have to be real tight, but tight enough to keep spinning when pressure is applied..

With the motor and arbor attached to the plywood it is time to wire the motor.  Take the extension cord and remove the female end.  You can wire this directly to the motor so when you plug it in the grinder starts up.  I choose to add an on/off switch.  I took a closed electrical box and ran the wires from motor to the electrical box.  I then took the extension cord and ran it to the electrical box and installed a regular light switch and switch plate.  Put on your grinding wheels, in my case a grinding wheel and a wire wheel.

Make sure everything is firmly attached, flick the switch and grind away.  There is a lot of vibration so it is best to clamp the plywood to a workmate or saw horses.  Now as long as there is electricity, you can grind anywhere.  I have found it to be extremely handy.

nylar7 months ago

Just for anyone trying to build one of these pulley systems, you would also need to acquire a block bearing or something similar to hold the arbor/mandrel in place. This doesn't seem to be noted in the materials list (or is being considered part of the arbor?).

DoDo729 (author) 1 year ago
Hi, thanks for looking and commenting. As for your questions, the arbour has a shaft with opposing threads on which to attach the grinding wheels. A 1 hp motor is more than enough and for me personally I would go with a metal arbour just for its strenght values, you sure wouldn't want it to collapse during grinding. Hope this helps.
yes sir,i will not want it collapse during grinding but finding a metal arbour is getting difficult where i live(india). so i was thinking to build mine from hardwood
Thank's for helping me & it has been long since you posted a instructable would love to see more from you :)
Regards
Bobblehead Einstein
Hi i have been attempting something similar & your instructable gave me new ideas for my project....so i wanted to ask you
Q1-how did you attach the grinding wheel in place?
Q2- will a 1 hp motor be enough?
Q3-a self made arbour from wood,will it work good enough?(or do i need to have a metal version of it?)
Thank's for the great instructable :)
Regards
DoDo729 (author) 1 year ago
Hi, thanks for looking and commenting, you should be able to use it by putting on a bigger pulley on the motor and a small one on the arbour. That way it should spin fast enough for grinding. Hope it works for you.
musick_081 year ago
I have a furnace motor, but its only 1/25 hp. would that be strong enough for this, or should i use it for a different project?
rimar20003 years ago
Excelent project! Congrats. What is the power of the motor?
DoDo729 (author)  rimar20003 years ago
Thank you, the motor is 1/3 HP. Thank you very mush for the patch, it is greatly appreciated. Love your projects as well. Thanks for looking and commenting.
pfred2 DoDo7293 years ago
What is the motor's duty cycle? I've had to not use some motors because they were rated for intermittent use, like garage door opener motors. If you find your grinder vibrating a lot try dressing and truing the wheel. Now make yourself a tool rest. My arbor style grinders I've made aren't too portable but I made a nice tool rest for one:

http://i.imgur.com/YztV0.jpg

http://i.imgur.com/RcLLI.jpg

Another grinder I made:

http://i.imgur.com/w1a4G.jpg

and another:

http://i.imgur.com/SX3pn.jpg

An odd one for wet grinding:

http://i.imgur.com/rC7Ts.jpg

Group shot:

http://i.imgur.com/nF8yR.jpg

I need to make tool rests for some more of mine yo!


DoDo729 (author)  pfred23 years ago
Hi, thanks for looking and commenting. As for the duty cycle, not really sure, just had the motor lying around. Checked out your grinders and tool rests. Very impressive. Will have to make a rest for mine now. Keep up the great work.
Thanks again.

Fraser
pfred2 DoDo7293 years ago
Seeing as it was a furnace motor you're probably OK. Look on the motor's name plate you should see the letters CONT on it and that'd be short for continuous operation. Most motors are rated for continuous use, just some aren't and those worry me.

When you make your rest try to adapt this design with a sliding table. With it you can do nice hollow grinding on chisel or plane blades. I know I did a bunch of welding and metal work fabricating mine but I imagine someone crafty enough could figure out a way to do it using easier materials to work with.

I think the important aspects are that it is angle adjustable, and there is the slot in the table rest for the sled to guide in. That was my prototype for my metal model. I determined it is better with a fence stop on just one side of the sled. Though that one works well too and I use it.

My next tool rest I I make I want to rip off the Tormek F style slider design sort of for my 3/4" arbor grinder. I seen the videos I just don't want to pay the thousand dollars! I need just the right sized pipe or rod in order to make it though.
GrinderSlide.jpg
CementTruck3 years ago
Where did you get the arbor? I cannot find any locally.

I've been wanting to make something similar for a while now and use it for Hawaiian style bone fish hook carving.
If you have a welder, you can make a good arbor using thick iron tube and two ball bearings. A lathe would be ideal, but it is not essential, you can manage to suit the bearings using thin steel sheet strips.
DoDo729 (author)  CementTruck3 years ago
Thanks for looking, I had the arbor in my garage for a long time, but you should be able to get one at most hardware or tool stores, if not check online, I know they are still available. Good luck in your search and thanks for commenting.
shipto3 years ago
excellent work, just one little thing I would get that belt lined up otherwise you will find your replacing it more often than you should.
DoDo729 (author)  shipto3 years ago
Thank you, you are right, actually the belt is lined up, it is just the way I took the picture, but a great point none the less, I will add that to the description. Thanks for looking and commenting.