Making Perfect Circles With a Belt Sander
4 Steps
Often, I find myself needing a wheel, plug, or round insert for something and don't have the round stock to make it. Here's the quick way I made a round cap to fit the winch in my small barn using a belt sander.
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## Step 1: Rough-Cut Your Circle

No real need for accuracy here.  Just insure the shape you cut is larger than the diameter of the finished piece you want.
SteveGerber says: Jan 20, 2012. 8:28 AM
Why not drive a finish nail through the center into a scrap board and rotate your work piece around and around against the belt sander?
bfk (author) says: Jan 21, 2012. 3:21 AM
Hi Steve:

That's an excellent question that made me think. I'll try to explain my logic.

My goal was to make a round object exactly 1.450" in diameter, no center hole, using the least amount of work. By eliminating the nail, the nail hole and the mathematical calculations of where to place them, I could save myself a lot of work, plus eliminate an unsightly hole.

The center of the object, was not important to the goal. By building the circle from the outside-in, the center was allowed to wander as the object was being shaped. As the object became perfectly round, the center found itself at the same place it would have been if it had been turned around a nail, but because it's location wasn't a priority, I didn't care where it was, even though we know where it was... At the exact center.

I achieved the desired result with half the labor.

Now, if I were making a wheel for a toy truck, something that would be mounted to an axle, I'd turn the piece in the traditional way (or use a hole saw as Dr Qui mentions below). The end result would be the same, but the concentricity of the circles would be a priority, so the way I'd build it would be based around that. From the inside-out, with the center solidly located and the outside shaped around it.

Did that make sense?

I hope so. If not, let me know and I'll try again. Thanks for making me think.
SteveGerber says: Jan 21, 2012. 8:10 AM
Just another thought. You should be able to arrange to make a hole only on one side by driving a finish nail 3/4 of the way through rather than all the way through, then clip the head off, drill a matching hole in your scrap board and pivot.  Actually rather than a nail you could use any stiff piece of wire or round metal (i.e. piece of a bike spoke, etc.).  Just drill an exact sized hole part way through your disc and into the support board.

I made a nice round deck for my Crokinole board by pivoting a piece of plywood through a radial arm saw.   At first you have to keep chopping straight cuts off but once it's almost done you can just spin it through the blade to make it perfect.  This game calls for a large hole in the middle of the board so the pivot point gets cut out anyway.
bfk (author) says: Jan 21, 2012. 8:40 AM
I love that! That looks easier than using a router, which is how I've usually made large circles (and it would save router bits as well). My cut-off has a backboard that'll have to be removed, but this project is certainly on my short list.

Thanks for giving me such a great outside-the-box idea... I'm headed over to your "follower's" list:)
pfred2 says: Jan 22, 2012. 8:24 PM
You don't have to remove your back board, just use an auxiliary table so you go over it.
bfk (author) says: Jan 23, 2012. 1:28 AM
Alas, there's only 1" between the top of my back board and the little laser thingy on the blade. The backboard does slide for angle cuts, so there might be an easy way of removing it completely.
Dr Qui says: Jan 20, 2012. 8:14 AM
Looks kinda complicated many steps involved. But interesting.

A cheap set of hole saws is a much faster way to get perfect circles, they would have a 6mm hole in the center but are perfectly round, but can be used in a pillar drill with the center drill removed on some sets.
bfk (author) says: Jan 21, 2012. 2:23 AM
I like the way you think... Hole saws would have been the preferred way to go for me as well, but this job required 1: an off-center hole for the pin and 2: a diameter of 1.450".

I could have used a 1.750" saw for the rough circle and sanded the plug to size, but that would have used up a lot of wood for a 1.450 plug.

Larger circles can be quickly cut to any size with a router and real small circles can be made with plug cutters, but custom mid-sized circles need to be turned.

It takes me forever to setup a traditional turning. This is an outside the box solution that isn't complicated at all...

1. Cut a rough circle.
2. Sand one side to size.
3. Spring clamp a couple of stops to the table.

It takes very little time, uses direct measurements and produces a clean part that only needs finish sanding.

Now... Would I use this method if I were making traditional furniture? Probably not... I like tradition. I still use my great grandfather's tools:)
kevinn675 says: Jan 20, 2012. 8:55 AM
thanks for a great instructable. I dont own a lathe nor a drill stand but I do own a belt sander..I can see another instructable coming here...
bfk (author) says: Jan 21, 2012. 1:27 AM
Thank YOU for your comment. My Dremel, drill press, band saw and belt sander are probably the most used power tools in my shop. They were all I needed for years until I started building furniture. I'm looking forward to your Instructable.
papagun says: Jan 20, 2012. 8:31 PM
It would perhaps be faster to drill a hole the size of the "axle" or "center pin" in the "back support" board being used here. Flip the workpiece over and stick the extending "center pin" into the hole. Slowly move that board (with the work or disk attached to it with the "center pin" and free to rotate) towards the running sander until the radius desired is reached and clamp the board in place. Then pivot the work to make a true circle with the "axle" in the center.

I know it is mentioned that the center of the circle is not important in this instructable. Most of the time, the center is very important, however.

I also would not put my fingers into an "enclosed space" this small with the sander I own. Too dangerous.
bfk (author) says: Jan 21, 2012. 12:50 AM
Thanks for your insightful comment. The goal of this project was to quickly make a plug that locks a handle to a winch. The pin in the plug is .093 off-center (to line up with an off-center hole in the handle, not the center of the circle). I probably should have waited until I finished the circle to drill and mount the pin to keep the Instructable less confusing. It was quicker to accurately sand the edge of the circle to the face of the pin (a measurable dimension) than locate, mark and drill a hole .093 off-center of a located and marked centerpoint (all calculated dimensions).

Measuring and tooling across the diameter can be twice as accurate as the traditional way of measuring and tooling to the radius (errors are doubled when working to the radius). Plus, no centering, math, holes, pins, or plug-filling needs to be done. Just a parallel surface, spring clamped to the table and a few shims. Very simple, very fast and very satisfying.

Keep your scrap wood stops lower than your workpiece and your fingers will always be behind your work. I grabbed what I had lying around, but I also like to live dangerously:)
throbscottle says: Jan 20, 2012. 4:07 AM
What a great idea - far better than my method of lathe-less circle making! Took me a while to understand step 3 but maybe that's just dyslexia saying hello. Can you devise a method for creating a centre in the piece whilst using this method? (I'm assuming the little peg is just to hold it with) Lefties rule, brother!
bfk (author) says: Jan 20, 2012. 7:18 AM
Thanks for your kind words. Step 3 reduces the size of the disk so you can fit it between the backstop and the belt sander. I suppose I could have described it better.

I don't exactly understand what you mean by "creating a centre", but if you need to locate the center of a circle, Phil B posted an Instructable at: http://www.instructables.com/id/Make-a-Center-Finder/

You can also buy them online, made of plastic and very inexpensive.

That peg fits a hole in the handle on my winch and has nothing to do with the circle making. I could have waited until the job was finished, but that was probably MY dyslexia kicking in:)
mruck says: Jan 19, 2012. 9:43 PM
Guys, you don't get a circle this way. What you get is kind of a "Curve of constant width" or "Reuleaux polygon". Check Wikipedia.
bfk (author) says: Jan 20, 2012. 2:14 AM
Thanks for the info. I may be wrong but I believe you would end up with something resembling a reuleaux polygon if you replaced the straight edged backboard with a "V" shaped rest. Even though the piece isn't technically rotating about an axis, a backboard that's parallel to the sanding surface will produce a shape of constant diameter (a circle). There could be some variation if the piece were allowed to slide back and forth across the sanding belt, as those things can be inconsistant due to their raised seam, but keeping the piece in one place seems to work pretty well.
darrellrisley says: Jan 19, 2012. 9:47 AM
NIce. Although, chucking the plug into a drill and sanding it might have been easier and more controllable.
bfk (author) says: Jan 20, 2012. 1:48 AM
Unless the piece is small, it's nearly impossible to maintain accuracy with a drill (at least for me). Plus it needs to be centered, and worse, fitted with an armature. A lathe is still the best way to form round things, but it's labor intensive and inefficient for jobs like making plugs for storage shed winches.

If a belt sander isn't available, a drill might still be used, but instead of turning the piece, think about turning a drum sander and shape the piece that way. Thanks for your comment.
koebwil says: Jan 19, 2012. 4:35 PM
It would also give better concentricity, but really a lathe would be the way to go here.
pj63 says: Jan 17, 2012. 1:20 PM
Great Instructable well written and easy to follow..... Oh Thanks for Plugging the Difficulties us 'Lefties' face on an daily basis..... Just Remember 'We Left Handers are Always RIGHT in our MINDS'.... pj
taroblaro says: Jan 19, 2012. 2:31 PM
No. We Left Handers are the only ones in our Right Minds.
bfk (author) says: Jan 17, 2012. 4:00 PM
We're also more creative, better at sports, inventing and love making... I may be wrong about one of those things, but no matter... Left handers are great!:)
paqrat says: Jan 20, 2012. 10:31 PM
I believe you failed to mention our humility.
bfk (author) says: Jan 21, 2012. 2:25 AM
:)
woodmagnet says: Jan 19, 2012. 7:20 AM