Flicker uses two brazing processes to build its frames: fillet and lug brazing. These brazing processes are far less common than welding and produce a frame that is more unique and visually striking.
Fillet brazing uses a bronze brazing alloy to join bicycle tubes together. It is a process similar to welding because it allows tubes to be joined together at virtually any angle. This flexibility allows for many frame geometries.
Fillet brazing is different from welding in that it does not create a small bead of metal, but a large radius, or fillet. Once filed and painted, the fillet gives the frame a seamless look as one tube simply flows into the other. The larger radius of the fillet, compared to a typical weld bead, provides a larger area for forces to be distributed.
Lug brazing joins bicycle tubes together by using a lug to hold the tubes and then melting a silver brazing alloy between the lug and tubes to hold everything in place. Lug brazing produces exceptionally strong joints because the joint is reinforced by the steel lug.
One limitation of lug brazing is frame geometry. Each lug joins tubes together at a specified angle that can only be altered by a few degrees in either direction. Because there are a limited number of angles, not all bike geometries can be built with lugs. Nonetheless, most road bike and many mountain bike geometries can be supported by lugs. Also, lug brazing can be combined with fillet brazing to expand the variety of frame geometries. We can expand the variety of frame geometries further by creating custom lugs.
Brazing vs. Welding
Take a look at the slide shows below to see the differences between fillet brazing, lug brazing, and welding.
Fillet Brazing Cross-section
Lug Brazing Cross-section
Benefits of Fillet Brazing
- Doesn’t heat steel tubes up to their melting point, reducing heat-induced stress on the tubes
- Has a large fillet to disperse joint stresses over (just like the arch in a bridge)
- Gives the bike frame a seamless look
Benefits of Lug Brazing
- Very low heat input, greatly reducing heat-induced stress on the tubes and lugs
- Lugs provide extra support to the joint and are arguably the strongest joint available
- Gives the bike frame a classic look
Benefits of Welding
- Melts tubes and filler metal together to form one molecularly continuous piece of metal
- Faster process that doesn’t require finishing after the weld, greatly reducing build time
- A nice weld gives the bike frame a clean, high-tech look