Jigs to Cut the Curvature of Braces

Do you remember when you first started making acoustic guitars?   Do you remember the first time you realized that you would have to curve the bottoms of the braces on the top and back of the guitar? Did you make a template and rout them? How about sand the bottoms of the braces with a large caul? My memory is only that the ways I devised to do this task were all onerous and difficult. My results were not always consistent and, almost always had to be carefully adjusted.

In the last few years I have come up with a way to cut those curved braces on a table saw. The results are absolutely consistent, and, if you utilize a good quality sawblade, the braces are ready to glue direct from the tablesaw.

I use two separate jigs. One is designed to cut a 25 ft radius for my top braces and the other is designed to cut the 15 ft radius for the back braces. These numbers were initially chosen merely because they matched the 15 and 25 ft cauls which I use for the gluing process.

The jigs and how they work are relatively straightforward. Obviously a table saw cannot  normally cut a curved line. However, the jigs take advantage of the inherent elasticity and strength of the spruce braces. For my purposes I cut the spruce stock into braces 5/8" tall. The thickness of the brace can be whatever you want; the important measurement is that they must be 5/8" tall. A brace that size can be bent to some degree before the wood will break. This elasticity is what you will be taking advantage of.

Let's take a look at the jigs.

Study the photos. The jigs are just a board with one square edge of any width. I used Baltic Birch plywood 5 3/8" wide by 22" long (longer than the finished brace). Drill and glue a 1/4" dowel at each end of the board. Make sure that each is the exact same distance from the board's long straight edge. These dowels act as stops for the brace at each end. On my setups, the dowels are 7/32" back on the 15" radius and 9/32" on the 25 ft radius. The next and most complicated part of these very simple jigs is the stop in the center. You can see in the photos that the middle stop is just a piece of wood glued in a certain distance from the edge of the board in the center. The distance from that stop to the edge of the board is what determines the ultimate curve cut in the bottom of the brace. After much experimentation, I determined that on my jigs that spacing was 19/32" for the 15 ft radius and 33/64" for the 25 ft radius.

Now comes the hard part. Somehow, we have to hold the stressed brace in place in the middle while it is cut. Initially, I tried a DeStaco type clamp. It worked but wanted to slip and, left a small hole in the brace where it was applying its' pressure. I just was not satisfied with that solution. As a result I threaded a piece of wood and created a 3/4" wooden threaded "bolt" (Thank you to the Beal Company for a great threader!). Now I would have a 3/4" wooden "clamp" holding the stressed brace. This has worked wonderfully for several years. Nothing has ever slipped or not been held securely. Lastly, I made a tall handle on the jig since I would need to run it through the table saw and wanted my hands well away from the blade.

With the jig made, I place the jig against a solid object (I use my rip fence) and push my 5/8" brace in the middle until it makes contact with the stop. Tighten the wooden clamp down and the brace is ready to be run through the table saw.

Set the rip fence on your table saw to the exact width of your board (mine is 5 3/8). Raise the blade high enough to cut the brace. Run the jig through the table saw. Notice that the blade will cut more at then ends than at the center.

It actually is cutting the curvature! Remove the cut brace from the jig. Notice it now has a uniform curve on the gluing edge. Check it to make sure that it matches your gluing caul. If not, or, if your needs are different than mine, you can adjust the amount of the cut by increasing or decreasing the amount of flexion determined by the middle stop. Once you get it the way you want it, you can cut braces as fast as you can run them through the table saw! And they are always exactly the same.

With these jigs making braces is now almost fun! Enjoy!