12" DIY Disc Sander

Homemade 12" Disc Sander

One of the things I use most in the shop is the little disc sander on my combo 4x36" belt / 7" disc sander. It's pretty lightweight and when I seen some examples on YouTube of others making a 12" size out of wood, I started thinking about my scraps and wondered if I could put something together for cheap.

The Motor

I bought a 1/2 horsepower 1750 RPM motor at a garage sale for $5.  The shaft is 5/8" and I'll have to rig something to mount the disc. A steal for $5, but then both the seller and I never knew if it worked at the time. It works!

I had to swap the starter capacitor leads to get the motor to run counter-clockwise (when looking at the shaft).

The Disc

I bought a piece of 1/4" thick aluminum from the metal supermarket. This is probably going to be the most expensive item in the build. I cut it down to 12-1/2" x 12-1/2" with a jig saw. I used some masking tape and clamped the piece down good before cutting. It's slow going but doable.

I found the approximate centre point.
Punched a dimple at the intersection.
Then using a caliper set to 6" I scratched a circle. I then went over the circle with felt marker.
On the portable band saw I cut the circle out. This was done in 8 small sections. I am staying outside the line as I will true the circle after it's mounted.
Voila! A 12-1/8" circle of 1/4" aluminum.
I found this sheave that has a flat face. It is 5/8" bore (to match the motor shaft), has a set screw and is about 3" outside diameter.
For mounting the sheave, I used four 10-24 flat head machine screws.
I placed the sheave directly on centre and drilled one hole. The screw and nut will help keep this in place while drilling the other holes.
On the face, the holes are countersunk with a standard 82° countersink. The idea here is that no part of the screw head is above the surface. Try to get them perfectly flush.

I used a little nail polish for thread locking of the machine screws to keep the nuts from working loose.
Here I have mounted the disc and have it ready for the spin test. You'll want to clamp or screw the motor down. At this stage we really don't know how much vibration will be present.

Once it's spinning, I put my shield on and used a rest and the edge of a file to true the outside of the circle.

Now the motor and disc are looking good, it's time to build a frame to mount the motor and allow for a table mount.

The Frame

In the scrap pile I have some salvaged 1-1/2" channel. It comes as bracing for large cardboard shipping boxes to keep them rigid. It's folded up 18 gauge so not the strongest thing, but when it's tacked together in a web it will be quite strong.

The basic frame measures 13" x 12-1/4" The 12-1/4" is to get us close to the diameter of the disc so we can add pair of vertical supports to hold the table.

The motor needs to be raised 3" from the bench so the disc will spin clear. Oh yes it looks kind of Frankestein but will work ok. I welded 4 x 1/4" NC x 1/2" bolts to the underside of the motor mounts. The space is 3 x 5" on centres.

The motor and disc fit on there nicely. Now to plan the verticals to support the table. I want the table to be adjustable over about 50°. (+5° to -45°)

Reusing some 3/16" x 3" plate I made these two vertical support for each end of the table. I drilled and welded a 5/16" NC nut to each of them. The other holes will accept a length of 5/16" threaded rod for support and precise adjustment.

I welded the support on to the frame and installed some 5/16" threaded rod to act as a truss.
Another view with the truss installed. The nuts can be adjusted to create some outward tension on the vertical support. When we tighten the table it won't bend the support towards each other.

This is a photo of the rod with the motor and disc sitting in place.

Here I have attached the angles to hold the hood and the post to put the switch on. The angles are hardware store 3-1/2" inside braces and the post is some 1" square tubing, about 16" long.
Here after some Royal Blue rust paint we're looking good to go for final assembly.




The Table

For the table I had two things in mind--an adjustable angle and easy to remove. Removing the table is necessary to change a sandpaper. In order to get the table to swing I need to get the pivot in the right spot. I played in AutoCAD to see where the pivot should reside. I determined that dead centre on the disc would be good.

The table can be made from anything flat. I chose some 3/16" steel that I had bought for some other purpose and cut it to 16" x 8".

Cut the plate to create a notch so that the table sits "around" the disc. The band saw works great for this.
Evening out the notch, trying to get a nice straight line. This will run parallel to the face of the disc so anything but a straight line will look off.
This should make a nice big table to work on.
I cut two 5-1/2" pieces of 1-1/2" angle for mounting the table. These will allow us to tighten the table securely without flexing the table.
Two 11/32" holes are drilled in each angle to pass the star knob or threaded handle to pass through.
Checking the range of table tilt angle. Looks good.

The Hood

To build a hood I opted for something simpler to work with than steel. I had some 1/2" plywood and cut it to 12-5/8" x 12-5/8". I drilled a 3/4" hole in the centre drew an arc with a radius of 6.25" This will give a nice round curve. I cut on the band saw and smoothed on the sander. From the bottom, I cut out up to the hole so this will slip over the motor shaft.

Test fitting over the motor shaft.

I cut a half circle, again 6.25" radius out of scrap 3/4" plywood.  Another cut at about 4" radius makes a curved strip about 2" wide. I cut this into "wedges."
The wedges are drilled, glued and screwed match the radius of the hood.

Once the glue is dry I cut a strip of 1/8" hardboard at 2-3/8" wide and 19" long. It's glued and screwed. Starting at one one and working around the curve. Any little excess is trimmed off at the finishing end.
I painted the hood black with a brush type enamel. Before I painted it, I glued and screwed two strips of 3/4" plywood to fill in the area next to the vertical table supports. This sort of seals the sides and gives more for the mounting screws to bite into.

I used some #10 pan head wood screws to secure the hood.

This is the hood and table installed.


The electrical is a basic switched circuit. I've included some photos to show what I did, but as long as you're safe, go for it!

Connect the white wires together. Then connect the green wires. Add a new piece of green wire, say 4" for bonding the motor. Tie them up with wire nuts.
Crimp some lugs on the black wires and connect to a switch.

Mount the switch in the 1110 box and put the plate on it. I made some red and green rectangles out of duralabel and red and green sharpies.

Finishing Up

I cut some label stock into the shape of an arrow. Stuck it on top of the hood.
Squaring up the table.
I am going to enclose the underside of the table with some sheet metal and add a vacuum hose attachment.

Here you can see the table tightened down with the bolts.

The clearance is close at 90 degrees. If the sandpaper disc isn't adhered properly it ticks on the way 'round.


This thing is really useful. I made a few videos which I will post on YouTube.

Bill of Materials

Motor: $5
Aluminum: $27
Sheave: $6
Screws: $2.50
Steel: $12
Miscellaneous (cable ties, wood screws, paint): $5
Electrical box and switch plate: $5.99
Cord: $5
Switch: $1.99
1/2" plastic bushing: $0.49

Running total: About $71.00


Unknown said...

Hi Dan, as usual, great design. How do you attach sand paper?

D. Comeau said...

Hi Dainius,

The sand paper is PSA (pressure sensitive adhesive) backed. Commonly sold under a variety of brand names and grits in this 12" (30cm) size.

Elizabeth said...

I have seen your video clip. very nice. Great post! I found it very useful. Love the final result. Thanks for the inspiration and the tips. toolsadvisors

Kristine Abat said...

Wow, thanks for sharing this very detailed "how to guide" of a homemade disc sander in this article! I love stumbling upon guides like these but don't know whether I can put a plan to create my own belt disc sander!

Alvin said...

As usual, it's been really a great post. Great job. Metersawgeek

George Hollis said...

Great post and am in the process of building a 12" disk sander. Will a 3600 RPM motor be to fast for the adhesive sand paper? Thanks

D. Comeau said...

Hi George.

The the further you move away from the center of the wheel the faster the surface speed will be. With a 12" disc, the outer edge will be flying around at over 11,000 surface feet per minute. This is very fast and will have an increased tendency to burn materials being sanded. It would be preferable if you can source a four pole (1800 RPM) motor.


Ferdidiver said...

Hi Dan ,

Thanks for the numerous amount of info on your website . As a newbie I am spending hours to view and take in all the info I can . God bless you for your generosity

D. Comeau said...

Thank you for your kind words. I hope that you can find something useful here.

All the best,