Making Perfect Circles With a Belt Sander





Introduction: Making Perfect Circles With a Belt Sander

About: Old inventor, reverted back to my 10 year-old self. A shop full of tools, a boat, race car, 3D printer and a beautiful wife who wants me to invent things for around the house... Now how cool is that?

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.

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.

Step 2: Rough Sand Your Circle

Same goes for the initial sanding.  Turn your piece smoothly enough to eliminate most flat spots.  Check the diameter of your work often.  Make sure you stay over your desired finished dimension in all directions.  When you get close, stop sanding. 

Step 3: Get Your Final Dimension

Now it's time to sand your circle to it's final dimension.  With your measuring device, determine how far over the desired dimension your circle is.  For me, my desired dimension was 1.45" and the smallest dimension of my rough circle was 1.48".  I would need to sand .030" inches off the diameter to meet my requirements.  By sanding off .015" (half the distance) all the way around, I should end up with a diameter that's closer to my desired dimension of 1.45".

Your circle won't be exact.  Measure your it to find out in which direction the smallest dimension is.  With the smallest dimension perpendicular to the sand paper, cautiously,using small increments, sand the circle down until you create a flat spot on one side.  Keep sanding and measuring until the distance across the flat spot to the opposite side of the circle matches your desired diameter.  Be sure you don't over-do it and go beyond your final dimension.  I've marked the flat spot on the disk I made to make it easier to see.  The peg poking out of my circle is off-center and matches the hole in the handle this cap is being made for.  It has nothing to do with this Instructable.

Now set up your tooling.  Any scrap you have lying around will do.  Lay a straight edge on your sander's stage, parallel with the sand paper.  Now, place your circle on the stage between the straight edge and the sand paper with the flat spot against the sandpaper. Move the stop forward until it stops, pinching the circle in the middle.  Clamp your scrap stop to the stage.

Next, take another piece of scrap and place it to the side of the circle (I'm left handed, so mine is on the left... If you're right handed, don't complain, just reverse it.  Us left handers have had to figure out reverse directions our entire lives:).  Clamp it in place and start the belt sander.

Use the small piece of scrap to keep the circle in place horizontally on the belt.  This will insure the same section of belt is sanding on your circle.  Rotate the circle, keeping slight sideways pressure against the small piece of scrap and backward pressure against the stop until you're able to rotate the circle freely with no grabbing.

Stop the belt sander and measure your piece.  I like to sand in smaller increments and sneak up on my dimension as opposed to throwing caution to the wind and grinding it all off at once.  Using .010, .015, .020, .040 & .050 shims placed between the stop and the circle, I can work down to the dimension I want without adjusting the clamps.

Step 4: All Done

All that's needed to complete the plug is to round the edge, finish the exposed portion and install it on the winch connected to the elevator in my barn.



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    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?

    5 replies

    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.

    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.


    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:)

    You don't have to remove your back board, just use an auxiliary table so you go over it.


    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.


    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

    6 replies

    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!:)

    I believe you failed to mention our humility.



    So glad i'm ambidextrous. ;0)


    I wish I was... Bet that's the reason I can't juggle:)

    No. We Left Handers are the only ones in our Right Minds.

    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.

    1 reply

    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.
    4. and turn your part.

    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:)

    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...

    1 reply

    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.

    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.

    1 reply

    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:)

    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!