Wooden Desktop Trebuchet

Step 4: Cutting the Joinery - Part 2

The frame crossmember (Part C) is going to seat across both long frame rails so it needs two sections removed. Rather than measure it all out, it's easier to just clamp the four sides of the bottom frame together and lay the crossmember in grooves in the long rails. Get it lined up by eye and mark out the sections where the rails intersect. That's where you're cross-lapping the crossmember just like the rails so mates up tightly and sits flat.

Now we're going to carve the uprights (Part E). One end will have a half-lap and the other end will have a groove carved in the end for the axle to ride in. The half-lap is just like the ones on the side rails. For the axle groove drill a 3/16" hole about half an inch or so from the end. The next step is to clear out the wood between the hole and the end of the upright. Cut a slot from the end to the hole so you can have a little room to get your knife in there and carve it out. Alternately, if you don't mind it being hard to get the arm out, you can just drill a hole a little bigger and thread the axle straight through the hole.