Step 4: Cutting the Joinery - Part 2
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.