I will try to make some clarity on this subject that is too often underestimated and misunderstood: what is the difference between a racing bike frame or a mtb steel welded tig and the same welded in fillet brazed? em>
Without going into too much technical speeches that the "common mortal" like me would not understand, I will try to explain in the simplest way possible by putting myself in the shoes of a very common person who wants an answer as simple and comprehensive as possible.
The difference is enormous and basically it is that the tig fuses the metals to be joined, while the fillet brazed "glues" them with the help of a lower alloyed metal alloy.
The latter is in turn divided into two types, a frame with conjunctions and a frame without conjunctions
After saying this, the passionate cyclist's question arises: What is the best method among the three?
Let's analyze the different methods and draw conclusions. Today the new steel alloys have exceptional breaking loads and therefore the companies that produce tubes for cycling can make tubes with very thin thicknesses, less than half a millimeter and through adequate heat treatments can withstand high stresses over a period of time very long (unthinkable with aluminum or carbon frames).
The tig as we have said must melt the metals to unite them so it brings the temperature above 1450 ° C and partly alters the balance of the metal and theoretically weakens it, in fact on all the frames welded with tig, regardless of the type of material (aluminum, steel, titanium) breaks occur just after the weld bead.
frame breakage due to tig welding
The brazed fillet being a "bonding" does not melt the metals to be joined so it does not alter the balance or at least it does so to a much lesser extent, this depends on the type of alloy / material used to join the tubes.
The alloys commonly used are with silver percentages ranging from 5% (the most used) to 60% silver (the least used), therefore temperatures ranging from 850 ° C to 550 ° C approximately. The higher the silver percentage, the lower the "bonding" temperature, therefore less stress on the tubes but more stress on the pocket being very expensive.
Few artisans use 50-60% silver alloys and their method advertises it with the words "Silver Fillet Brazed".
Pro : ease of processing, cleanliness, lightness, freedom of geometry.
Cons : possible breaks with very thin tubes.
Pro : stiffer than the tig, it does not alter the balance of the tubes, pleasant to look at (looks like a monocoque), freedom of geometries like the tig .
Cons : slow processing, more expensive, a few dozen grams heavier.
Pro : undisputed retro charm with machined and chrome-plated joints
Cons : slow processing, more expensive, bound in the choice of angles.