Oval by Geometry

Art_OpenerIn late 2010, I listened to furnituremaker Fred Roman talk about ovals and how to lay them out using geometry. I had always used a string method in the shop, and when I was in the home-building field, we used two framing squares. These days I use SketchUp.

The way he did it seemed point on and easy. The same way you could swing the arcs with a trammel, you could swing a router using a circle-cutting jig. I pushed for this to be an article (shown left) in Popular Woodworking Magazine(PWM). B_PlanA contract was executed and before the piece ran in the magazine pages, I had left to pursue other interests. Of course I read the article when it was published. The right-hand photo is the layout, but you should read the article to get the details. (PWM doesn’t sell the article as a stand alone, but you can pick up the August 2012 issue (#198) at shopwoodworking.com.)

I kept the method in mind for whenever it may be needed. That time arrived this weekend when Dave Griessmann was in the shop working on a Federal-period table. IMG_1187His top was ready to transform from a rectangle to an oval, so we pulled out Fred’s article to make it happen. Dave laid out the oval and was contemplating how to make the cut when I reminded him that he could swing the router to get the job done. He decided to router-cut the larger radii. The length of my often-used circle-cutting jig wasn’t long enough, so we substituted a length of plywood. At one end we drilled a 1″-diameter hole to match the outside radius of a guide bushing, at the other end we drilled a 3/16″ hole as a pivot. (We were working on the underside of the top.)

A couple of adjustments were made to the jig so we cut exactly at the layout lines, and so the jig could spin without any interference from the clamps used to hold the top. IMG_1189Everything was set and ready to go, so Dave powered up the router and made a light pass. The depth of cut was 3/4″ so we set up to make the entire cut in three steps, and he cut only half of the top. When we finished that half, the top was spun so the remaining half hung off the table and the step process was repeated. The cuts were perfect. In fact Dave wanted to setup and cut the ends the same way, but I persuaded him to cut those at the band saw and clean the edges using a disc sander. While he (and you) could do that, I think it’s much easier to trim the second radii so you don’t nick into the already cut edge. There’s no sense in taking the chance given the leaves of his table were easily cut at the band saw.

The entire process worked like a charm. I will use it over and over when I run into ovals – large ovals – in my work; small ovals are too easily cut using my band saw.

I included the photo below to show you the nifty clamping method we used to hold the arced edge for the second set of cuts. Our clamps could not reach the workpiece, so we lapped pieces onto the tabletop then clamped the scraps in place. This is a handy trick in a pinch.

Build Something Great!

Glen

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2 thoughts on “Oval by Geometry

  1. Glen,

    The article came out great, but I would have loved to have you there at Pop Wood and give me more of your input.

    Cheers,

    FR

  2. I just took a class from Scott Grove at Marc Adams. He has a different way to handle this that sets you up for doing the edge and inlay. It is too much for me to explain but look him up sometime.

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