This is the Bay State guitar that I work on sporadically. The back has been off as long as I've had it, more than 20 years. When I got to the point where I was going to put the back on again, there was not a single spot where things lined up. I had the "L" brackets from a previous project, following Frank's example. No matter how I tweaked it, getting rid of a bulge in one place would only produce another bulge somewhere else. The turnbuckles were helpful at keeping the waist lined up, but, again, needing constant readjustment. Half an hour or 45 minutes were about all the frustration I could take. The lesson that I've learned over the years is that bad thing happen when I continue in that situation. Better to go do something else, and come back later. After multiple sessions, I think it is finally ready to glue.
Thanks Frank for all your great examples
Not as adjustable as mine. It's a good thing to be able to place the clamp on exactly the right spot on the rim, no matter what the shape of the guitar is, and at the place where the side is bulging out the most. The clamps don't have to be as many and evenly spaced as in this jig, no need for a caul to spread the force either, just placing the clamps in the right spot will work fine.
My softwood (fir) plywood backplate is dispensable, I have changed it one time in 10 years when the old one got too many holes.
Here is a picture of the glue up of the back. I used "Old Brown Glue" at 140 degrees, for the longer open time. Even then, it felt like forever. My fingers are still crossed.