Making Perfect Circles With a Belt Sander





Introduction: Making Perfect Circles With a Belt Sander

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?


    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


    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.