A frame jig is such different device depending on what you aim to achieve with it. Basicly just for measuring you only need a flat table with a custom clamp where you can bolt the frame in exact position from time to time and a fixed rigid, true square around the frame, to use as a secure support to measure from.

A frame jig is really different if you want to have it for straighten bent tubes or correct angles that is out of kilt, then the rig needs to be really strong, boxed, still versatile and adjustable to support chains and pushing/pulling hydraulic tubes. 

And if you want it for welding tubes in position, then you may want an open jig, maybe just a flat table where you can add or take away and maybe weld supports and helping devices on.

Can you combine all of that, measure, straighten and repair an assembled bike as well as a disassembled frame, and a jig that is light and possible to stow away in a flat pack on a shelf, then I am definitely interested of a drawing of that!

It also has to be cheap :-)

Billy, don't dive in with a welder or start cutting tubes. 

You should not steel weld near any original joints. As Carl-Erik says, all joints are brazed. If you steel weld on the bronze it will melt the bronze into the steel and form an alloy with all the strength of soggy cardboard.In addition, arc welding on the cast malleable lugs can also make them brittle. Any repairs near a joint need to be checked, and repaired with bronze.

Cutting and retubing is not a good solution either, except in extreme circumstances.  Many of the joints have an internal spigot which is brazed in. You may well find bronze spatters several inches away from a joint, and cutting and welding on them will just create more problems. 

Do a lot of frame repairs here, and the most difficult ones are fixing other peoples repairs.

Vahan Dinihanian mentioned this in a facebook discussion a while ago, just for information..

Vahan Dinihanian: I used to talk to George Yarocki in depth about metallurgy and we found that the strongest and our favorite brazing alloy for repairing frame joints was MG130FC Flux coated brazing rod. super high tensile strength brazing alloy. I think the last place i purchased it was through Castolin Eutectic.

By the way, there is no particular reason not to use the rod Vahan is suggesting, its just that George did not use it. A brazed repair will work particularly well with it, but for bronze welding, ie the majority of repairs on a frame, you will have too much flux after the initial "tinning". On large repairs I tin using a 1/16" rod to tin, and move up to 3/32" or 1/8" rod for filler.