Mike,
That's a great job on that jig!  Well done!

NB, thanks for the photos they help me really understand and I may be able to construct one now.

Bob

Greetings All - Here comes the work up, description and photos of my assembly fixture. I had no idea there would be even any interest in this tool when I designed and built it. Like I said, this is in response to a posting I made about converting all my truss fuselage plans to keel type plans and would build a fixture to make the end result possible. So, I'm going to start off with the base and it is simply a piece of 1 x 8 poplar I had in my wood shop. I cut off two pieces for the uprights and glued them to the base as seen in the first photo. This decides the clearance for any future pieces as this is turned over to work on the other side. - see my pic of my Gee Bee vertical stab that just barely made it, plan accordingly.

The next part is the actual assembly fixture and it is built on a piece of 3/16 Birch plywood I got at Michaels. The idea is to have a solid plane to built all the other parts on then open up the middle to allow access. The frame of the fixture is assembled with 3/8 square popular pieces from Lowes or any where else you want to source them. I'm a big fan of simplicity and using these parts eliminates cutting bigger parts down to size (we do enough of that in the modelling process). The only other square part is the 1/2 square piece on the outside of the frame and I did that to use it to align the cross pieces.

The assembly is very straight forward at this point. Glue the 1/2 inch square piece on either long manufactured edge of the plywood (the manufactured edges are usually very straight). Cut the Mini Trak (Kreg Manufacturing P/N KMS7509 from Amazon or Woodcraft) in half so each piece is 24 inches long. It comes with small flat head screws for attaching it. Snug it up tight to the 1/2 inch piece and screw down to the ply. Cut a piece of 3/8 square 24 inches long and glue to the ply snugging it up to the mini trak. Do the same to the other side (except the parts there are all 3/8 square) knowing this will decide the opening for any future fuselage assemblies. The opening in mine is 7-1/2 inches. On the ends I glued 2 3/8 square pieces together and cut to fit between the horizontal rails you just installed. The top is now complete except for cutting out the ply between the rails and you are done. Place the assembly fixture on the base and align fairly square and match drill thru the 2 end pieces into the base and install a dowel in the base only. This allows the top to be inverted and replaced back on the base to work on the other side. I'm well ahead of everybody at this point so I will tackle the crosspieces and their placement and alignment in another installment rather than complicate this any further. Just an note on cutting and gluing; try to make everything as square and solid as possible. The more square the better the cross member will align and work but absolute accuracy is not required, just our customary good workmanship. Hopefully I will have the Gee Bee off the frame and can show how to align and use the frame.

I'm on this site every day so post any questions and I'll be back with answers same day.