Frame-building - Has anyone actually done it?
For my sins I have to admit that I have built quite a lot of frames, having started way back in about 1953...but it wasn't until about 1958 that I was allowed to wield the torch as well as a file and hacksaw.
In those days the principle source of heat was a torch burning coal-gas ( the same stuff you cooked your meals on) enhanced by compressed air. The flame was a very large soft quite hot one that had the advantage of wrapping around the lugged joints, thereby providing a thorough heat that emcouraged the brazing spelter to flow through all the joint.
However the heating up process took longer but there was hardly any danger of overheating the tubes. Cast lugs were often used in those days and these were thicker and heavier - meaning that they took longer to heat up than the tubes..and the later pressed steel ones. This is one of the reasons that the lugs on older frames were often filed and thinned down..both to provide a better cosmetic look but also to reduce heating times.
Then along came oxy-acetylene, and oxy-propane..but that's a different story. If you know how to gas=weld and braze with oxy-acetylene that's fine..it's quicker, very effective and essential for anyone thinking of bronze-welded ie lugless frames.
However misuse of this heating soource can ruin a frame in seconds...My advice to anyone thinking of starting to build a frame is to take some lessons in brazing..It is simply esential to know how to use the torch. Once you are proficient then you have a reasonable chance of building a decent frame. Remember that even with the best jigs, the brazing/heating process can create stresses and distortion that you would not expect..the town-gas-compressed air method minimised this problem.
Use a brazing rod such as SIF-Bronze that flows around 850degrees. as for silver soldering..OK excellent stuff, flows about 200 degrees lower temperature....but is SO expensive..and needs great care not to be overheated. Too much heat and you burn the joint, and waste a lot of money spent on the solder..and possibly the steel tubes. Silver-solder is not gap-filling ie the gaps between the tubes and the lugs have to be very close..closer than with SIF-Bronze..and they have to be exceptionally clean..and you have to have the correct flux, a slightly higher temperature one than you would use on non-ferrous metals such as brass, copper, silver..
Oxy-propane is a good choice for the job..not quite as hot..and the gases are cheaper and more readily available..but it takes more time to heat the joints..and its quite clean. Most builders use oxy-acetylene because they know what they are doing..it's quick..and because Once Upon a Time when they bought the welding kit, the gases were cheap as was the rental for the cylinders...But these days..well you've heard what inflation can do!
As has been noted by others..you do not necessarily need a jig..but you do need to know how to test for alignment at various stages in the build process. If you get the first joint wrong - which is usually the seat-tube into the bracket shell..then everything else that follws will be wrong too..and out of alignment.
Otherwise it's great way of passing your time down in the garden shed. Do NOT braze or weld in your house as there are certain gases that are given off that can be dangerous. Always weld/braze in a well-ventilated room..but avoid draughts...
) on there and his frame jig was a sheet of plywood with nails hammered in, between which he placed the tubes and then brazed them looked totally archaic but worked beautifully (for him).
