Tempered - Handcrafted Down Under
TIG Welding vs. Fillet Brazing for Steel Bicycle Frames
The first thing we get asked is questions regarding the use of fillet brazing on our latest batch of Australian Made frames versus the more commonly used TIG welding method.
So, before we dive into the details, let’s first break down what TIG welding and fillet brazing actually are.
TIG welding uses an electric arc to melt both the base metal (the tubes) and the filler rod, fusing everything into a single solid piece. The resulting TIG weld bead creates a very small radius between the tubes.
Fillet brazing is different. It heats a bronze or silver filler just enough to flow between the tubes by capillary action, bonding the tubes together without melting the base metal. With fillet brazing, a larger, radiused transition is created between the tubes. This transition is known as the fillet.
But which is better?
As with most things in this world, the answer is more nuanced than simply saying one is better than the other. Getting to that answer takes a bit of context—so let’s dive in.
Pros and Cons
The TIG welding process is fast and uses relatively little filler material, with minimal post-weld cleanup required. However, it involves very high temperatures (over 1,540°C), which can weaken thin-walled tubing by creating a pronounced heat-affected zone (HAZ). It takes a high level of skill to avoid warping or burning through the tubing—especially when joining tubes with different wall thicknesses.
Fillet brazing uses much lower temperatures: around 870°C for bronze, and even lower (approximately 650–760°C) when using silver. These lower temperatures help preserve the original mechanical properties of the tubing and significantly reduce the risk of warping. Because the base metal is never melted, burn-through cannot occur.
Fillet brazing is, however, a more time-consuming and labour-intensive process compared to TIG welding. It requires extremely accurate tube fitment, meticulous cleaning (both inside and outside the joint), and the use of flux, which must be thoroughly washed off after brazing. Finally, achieving the smooth, seamless appearance of a fillet-brazed joint takes additional time and a high level of skill to file and sand the joint by hand.
Strength Comparison
When done correctly, both methods produce joints that are stronger than the tubing used in a bicycle frame.
To clarify: while the bead of a TIG weld is inherently stronger than the bronze or silver used in a fillet-brazed joint, the weld or braze itself is rarely the point of failure when a frame is overloaded. This is because bicycle frame tubing—including BMX frames—has relatively thin wall thicknesses. In practice, the tube will fail before either the TIG weld or the brazed joint.
From a mechanical engineering perspective, stress concentration factors increase dramatically as fillet radii decrease. Sharp corners and small radii create stress concentration points where forces are amplified. The larger radius of a brazed fillet provides a more gradual transition between tubes, resulting in lower local stresses compared to a TIG-welded joint.
Fatigue Resistance
Because TIG welding creates a heat-affected zone where the steel’s microstructure is altered, this area can become harder and more brittle than the surrounding tubing. Harder, more brittle materials are generally less resistant to fatigue cracking over repeated load cycles.
The combination of a harder HAZ and a sharper transition radius in TIG-welded joints can promote fatigue crack initiation over time. In contrast, the more ductile materials used in brazing, combined with the larger fillet radius, create a more forgiving transition that better resists fatigue-related failures.
There’s also an aesthetic consideration. Fillet brazing produces smooth, flowing joints that many riders and builders appreciate for their handcrafted appearance.
Final Thoughts
Both TIG welding and fillet brazing produce joints that are more than strong enough for bicycle frames—including BMX frames.
TIG welding is more commonly used because it is faster, cheaper, and less labour-intensive. In a factory setting, where large production runs are required, the time and cost savings are critical.
For small-scale production or limited runs, those factors become less important. That’s why we chose fillet brazing for this particular batch of frames.
If the primary goal is cost efficiency and high-volume production, TIG welding is the better choice.
But if the goal is to create something distinctive—something that highlights craftsmanship, detail, and the handmade nature of the process—then fillet brazing is, in our view, the clear winner.