Don, first a correction to my post. The minimum size of the minor axes is 8”, I had originally stated 4”. The maximum is 20”. One additional dimension is that the difference between the major and minor axis can be no more than 6”. I’ll use this jig to make oval cutting boards of various sizes with the most common size being 10” X 16”. Depending on what sizes you need you can make the base smaller or larger. That’s just to give you a background on my jig.
The base is 5.5” by 5.5”. You can make the base larger or smaller, depending on your need, but the length and width must be exactly the same size. This is due to the way I made it. I glued ¼” plywood to ¾” poplar and trimmed it on the table saw to the 5.5” dimensions. At this point there are several ways you can cut the grooves and it depends on what tools you have and how you’d like to go about it. Here’s how I did it.
To form the base: I mounted a 14 degree dovetail bit in my router table. You can use any angle you like. I set the height to 5/8” so it wouldn’t cut all the way through the poplar down to the ply. I wanted the groove to be about ¾” wide at the top. Depending on your bit you’ll have to adjust the fence but I set it to cut a little past the center line of the piece. I then ran the block along on all 4 sides and that formed the groove perfectly centered on the block in both directions. I then used the table saw to knock off the 4 corners, forming an octagon. The reason for this is, if you don’t, the standoffs on the arm that hold the router will hit the edges when routing a small ellipse.
One additional thing, I drew a center line through the bottom of each groove. Where the center lines crossed, which is dead center in the base, I drilled a 1/2". That hole allows me to line up the base with the center of the board that I'm going to route.
To form the slides: I used a 12” long piece of poplar to form the slides. I milled it to 9/16” thickness. I did this so the slide wouldn’t quite touch the bottom of the groove to avoid it getting jammed with sawdust. That was my choice. Many jigs I found do go the full depth. You can use the same router set up to form the slides. If this works for you I’d suggest this way since you’re already set up for it. I had a bit of a problem, probably my own ineptitude, so I decided to use my table saw. Using a digital angle gage I set the blade to 14 degrees and ripped the strip of poplar so the top (the smaller dimension) came out to ¾”. I then cut the piece into two 1 1/2“ pieces. i used a 12" piece because it was easier to handle. The rest of the strip went back into my scrap bin.
I drilled ½” hole in the bottom of the slides deep enough to accept a washer and so that the machine screw (1/8”hole) that attaches to the arm is inset below the surface.
The slides do glide fairly easily but a little wax make them slide easier.
I hope this helps. If you have any more questions or would like more detailed photos please let me know. Let us know how it comes out.
Last edited by Barry747; 05-26-2016 at 11:03 AM.