What is the difference between a steel frame TIG-welded and the same frame built with fillet brazing? I will try to shed some light on a subject that is too often underestimated and misunderstood.
— Vincenzo Forgione

Without getting lost in overly technical talk, I will explain it as simply as possible, putting myself in the shoes of someone who wants a simple and complete answer.

Vincenzo Forgione silver fillet brazing a steel frame

In short

  • TIG: melts the metals to be joined.
  • Fillet brazed (brazing): “glues” them with a filler alloy that has a lower melting point, without melting the tubes.
  • Fillet brazing in turn comes in two types: frames without lugs and frames with lugs.
  • For my frames I use Silver Fillet Brazed: brazing with alloys that have a high silver content.

Having said this, the keen cyclist will naturally ask: which of the three is the best method? Let’s look at the different methods and draw some conclusions.

Today’s tubes: very thin walls

Today’s new steel alloys have exceptional tensile strength, so the companies that make cycling tubing can produce tubes with very thin walls, less than half a millimetre. With the right heat treatments these tubes withstand high stresses over a very long time. This is exactly why the way the tubes are joined matters so much.

How TIG welding works

As we said, TIG has to melt the metals to join them: it takes the temperature above 1450 °C and partly alters the balance of the metal, theoretically making it more brittle.

In my experience, when a TIG-welded frame breaks, whatever the material (aluminium, steel, titanium), the break occurs just past the weld bead: the photo in the comparison below shows a crack right next to the bead.

How fillet brazing works

Silver Fillet Brazed brazing on a steel frameSince fillet brazing is a kind of “gluing”, it does not melt the metals being joined: so it does not alter the balance of the tubes, or at least it does so to a much smaller extent. This depends on the type of alloy used to join the tubes.

The alloys commonly used contain from 5% silver (the most common) up to 60% (the least common), with working temperatures from about 850 °C down to about 550 °C. The higher the silver content, the lower the “gluing” temperature: less stress for the tubes, but more stress for your wallet, because these alloys are very expensive.

Silver Fillet Brazed: the technique I use

Few craftsmen use alloys with 50–60% silver, and they describe their method as “Silver Fillet Brazed”. It is the technique I use to join the tubes of my frames: slow, handmade work that, in my view, makes the difference.

Pros and cons, in my experience

TIG weld: an obvious crack next to the weld bead
TIG-welded framePros: easy to work, clean, light, freedom of geometry.Cons: possible breaks with very thin-walled tubes.
Fillet brazed joint without lugs on a Forgione frame
Fillet brazed, without lugsPros: stiffer than TIG, does not alter the balance of the tubes, pleasing to the eye (it looks like a monocoque), freedom of geometry like TIG.Cons: slow work, more expensive, a few tens of grams heavier.
Building a lugged steel frame
Fillet brazed, with lugsPros: undeniable retro charm, with worked and chromed lugs.Cons: slow work, more expensive, limited choice of angles.

From the workshop: Silver Fillet Brazed joints

Vincenzo Forgione building one of his steel frames

Here are some photos of the building stages: from the freshly brazed joint to the prepared frame, ready for finishing.

Would you like a custom Silver Fillet Brazed frame?

Tell me what bike you are looking for: together we define the type of frame, tubing and measurements. I also use the same technique to repair steel frames.

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