1/8" balsa I-beam wing spars

I made these on a CNC router, but it can be done carefully using a std. router/table w/fence and a simple jig you can make.

It's a 3-pc. spar, assembled w/thin CA. You will need (x2 pcs.) 1/8" x 1/2" balsa strips and (x1) 1/8" x 1/4" balsa strip; the desired length of the spar (not necessarily the span of the wing).

Make a jig of the same length as the balsa stock you're using; with a lip on the end, that will engage the stock, and "pull it through" at the back-end while routing. (use the router/table to make the jig... i.e. rout an open joint; 1/8" deep x 1/2" w. on the edge of the jig; the length of your balsa stock.) This jig serves 4 functions; it will hold your work-piece "flat" (for a consistent "depth" joint) hold your pc. against the "fence" while running it through (for a consistent "width" joint) the "lip" acts as a "push-stick"... and finally; the jig protects your fingers while routing these sm. pieces.

Once you've made the jig; Set up your router with a 1/8" straight cutter; set to 1/16" depth, and set the fence for a 1/4" offset; on the cutter's center. Place one of the 1/2"w. balsa strips in the jig, and feed it through the router; keeping the jig tight against the fence. Do the same, for the other 1/2"w. pc.

You now have the top and bottom of your I-beam, with 1/16" deep x 1/8"w. "channels"... running down the center; into which you will insert the 3rd 1/4"w. balsa strip. If your balsa is 1/8" strong on thickness; you may have to lightly "block-sand" the 1/4"w. pc. to fit into the channels. A snug fit is desirable... because you want the thin CA glue to "wick" into the joint, for optimal strength. Be sure to assemble/glue-up on a level surface.

This makes a VERY STRONG and VERY LIGHTWEIGHT wing spar, that measures; 1/2"w. x 3/8" thick, x your design length.  Give it a try on your next built-up wing.