CHAPTER 3 - About the jig
I get more questions about the jig than about anything else associated with the project. So I finally decided to devote a section just to the jig.
The drawing should give you a general idea about how the jig is laid out. Roughly, there are two 2x4 uprights, two 2x4 crossmembers top and bottom, and a 4x4 crossmember at a good working height (waist level). The feet are spare 2x4. My jig was made of cedar, which is drier than pine and smells much nicer. If you are building in your living room, the latter is an important consideration!
How you assemble the jig is not important, though you will want to be able to remove both the top and middle crossmembers while you are building the wing. I modified rafter and post brackets to work with carriage bolts, which increased the cost greatly but allowed me to disassemble the jig at will - important if I needed to move.
The diagonal lines on the drawing are not dimensional (sorry for the resemblance) but indicate where bracing should go. I used threaded rod directly through the wood and attached with bolts and washers, and turnbuckles to give me adjustment capability.
Don't get too hung up on jig perfection. Remember, this is really a 'fixture' in manufacturing terms - its purpose is to hold parts in alignment during assembly. The most important characteristic is stability; your parts should not move while you are working on them. You should never rely on your jig as a standard for alignment, but should check the parts themselves. I usually make sure one upright is vertical so that I can check the jig for movement. However, it has never moved on me even while working on the wings.
Speaking of the wings, I used pierced angle iron to support the spars, with flat iron bracing. Once the main spar was clamped in place I removed the middle and top crossmembers whenever I needed access to the wing on that side. Put all your angle iron support to the inside of the jig or the uprights will interfere with your access to the wing.
I attached a power strip to the outside of an upright, and used nails and hooks to allow me to hang other tools and parts in convenient but out of the way places. The bottom crossmember made a handy drilling table in a pinch. When starting a work session, I would check the jig for movement, then recheck whatever was in the jig. This is good practice no matter what kind of jig you are using. My jig is currently in storage after the successful completion of all my flying surfaces; I'll resurrect it if I build another RV.