MEASURE TWICE, CUT ONCE
These jigs allow accurate cuts in large panels.
SHOP OWNER: David Yoho
LOCATION: Mechanicsville, VA
Whoever said, "necessity is the mother of invention", sure was right. Years ago, when I first started building cabinetry, I found I needed a way to make straight crosscuts in plywood sheets and large panels. A full sheet of ¾" plywood is too cumbersome to cut in half on a tablesaw. I found using a circular saw was a better option. In addition, when it came to cutting dadoes in case panels, I found the router to be a good solution. However, using the circular saw and router for these tasks had some problems I needed to solve first. One problem was getting a straight cut across the width of a large panel. The other problem was how to know exactly where the bit or blade would cut in relation to my layout lines.
After some brainstorming, I came up with an idea for a positioning jig. Since I already owned several sizes of Clamp 'N Guide clamps, I could utilize them as my straightedge. This would act as the guide for a router or saw. Once I made the jig, it also aided in positioning the clamp. The first step in making the jig is to position the clamp on a scrap piece of stock, and use a square to make sure the clamp is at 90º to the edge of the wood before clamping. Next, use a pencil to mark where the edge of the clamp is on the scrap piece of wood.
In these photos I'm making a jig for a 12.3 millimeter straight bit to cut dadoes for ½" plywood. After installing the bit in the router, I'm ready to cut a dado in the scrap wood using the clamp as a guide. The depth of cut here doesn't need to be much.
After cutting the dado, remove the clamp and crosscut the piece on the outside edge of the pencil line made earlier. I also cut off any excess on the other end leaving about ¼" to ½" on the other side of the dado. It's important that the first cut, along the pencil line, is as square as possible. I like to mark them to identify the size of bit used. I also indicate on it which router was used since there can be a difference in the size of bases.
To make a dado in a panel using the jig and clamp, I measure where the dado needs to go and use a pencil to mark a layout line for the dado on both edges of the panel. Marking X's on the waste side of the line is helpful in identifying where the bit needs to cut. After positioning the clamp across the panel, I use the jig to locate the correct edge I need to cut. Just butt the jig up against the clamp edge and move the clamp until the cut edge in the jig lines up with the layout line. I usually start with the line closest to me. Then I adjust the far end of the clamp. Before locking the clamp in place, I double and triple check both lines with the jig. Once locked in place, I guide the router with the desired bit depth already adjusted, along the edge of the clamp and cut the dado. Be sure to hold the router against the clamp edge and not twisting it if possible. If the bit is not centered, this will cause the dado to be cut a little wider than expected.
I've made several of these jigs for the various size router bits I use. I also have one for use with my circular saw. The procedure for making it is the same. There's even one for cutting dovetail grooves. While I don't think this is an exclusive idea, I had never heard of or read about it anywhere before. It's not very high-tech but it sure gets the job done in my shop.. . . David Yoho
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