My question is how much does the quality of the weld have on the longevity of the bike frame?    A few years ago, a group of us went to a bike show with many bike builders.   Afterwards, we were looking at the pictures of several and noticed that some of the welds had small gaps or appeared uneven.  Most of the welds appeared great-“looks like dimes” as a friend who welds for a living would describe a perfect weld. What gives strength to the weld or does a weld require a perfect appearance to have strength？

So — it depends first on what type of welding we are talking about. And what material we are speaking of. Formigli currently builds a lugged steel Classic frameset and a fillet brazed steel frame called The Cellini. 

Formigli steel frames, we do not use TIG welding. Not because I don't like TIG — absolutely not. TIG welding is extremely strong and very resistant. But TIG fusion goes beyond 1000°C.

And with steel, there is a fundamental principle: the less we bring it to very high temperatures, the better it is.

The real issue with steel is not the weld itself — because even a weld that is not cosmetically perfect can still be structurally strong. The issue is what happens to the tube when it is heated to very high temperatures and then cools down.

If you bring steel to 1000°C and then let it cool, it experiences what we call thermal shock. It has a long way to cool down, and during that cooling process the steel can change. It can become tempered — harder, more rigid. And when that happens, the failure often doesn’t occur at the weld itself. It happens about one centimeter away from the weld, in the tube that has been altered by heat.

That is why, on our steel frames, we braze using a high–silver–content alloy and brass. These materials melt at much lower temperatures — around 500–600°C. At these temperatures, the steel tube remains essentially in its original state. It does not suffer thermal shock. It stays intact.

For me, that is the key.

With TIG welding, once you’ve done it, it’s done. There’s nothing more to do. It’s clean. TIG doesn’t leave slag or residues — there are no substances to remove. Once you finish a TIG weld, it’s finished. It’s much faster to do TIG.  With silver brazing, the work takes more time. After brazing, we must file the joint and shape it by hand. It is slower, more labor-intensive, a lot of hand work. 

But I prefer silver.

When we speak about a “perfect-looking” weld — like a row of coins — we are usually referring to TIG welding.

And honestly, you have to be very skilled. TIG welding requires a lot of experience, and also continuous practice. It’s something you need to do regularly, even every day.

When you see small holes in a weld, it means air was trapped inside— which means the weld is not continuous. Yes, technically it’s a weld that wasn’t done properly.

That said, in steel, the presence of a little air usually does not create major problems. It generally doesn’t cause significant issues.

The problem can arise with aluminum. With aluminum, you must be extremely precise when TIG welding. It cannot tolerate trapped air — otherwise it can fail or crack.

And with titanium, these holes or irregular weld, this can be serious. Titanium require extreme precision — a very high skillset and constant practice to execute seamlessly. 

Steel is more forgiving. Thin bicycle tubes are delicate, and for me the priority is to avoid excessive heat.

There is also something philosophical here. The world of welding is almost like religion — everyone has their own belief. A builder who has always welded with TIG will tell you they have never had a problem, that their frames never break, and that TIG is the strongest system. And they are not wrong. TIG is very strong, if done well, and depending on the material of the frame. 

But in my view — my “religion” — Its welding steel and brazing with silver at low temperatures.

When I began building frames in Mugello, near Borgo San Lorenzo, an elderly man from Scarperia — a town famous worldwide for knife-making — used to visit the workshop. He had worked steel his entire life. He would tell me: “As long as you build here in Mugello, you will have the best welds.” He believed the air — dry, low in humidity — was ideal for working steel. But more importantly, he would always repeat: never bring steel to unnecessary high temperatures. Because when steel cools, it does not always return to its natural state.

That idea stayed with me.

When I learned to build frames with Cino Cinelli, we worked almost exclusively with high–silver–content. TIG did not exist in his world. In those days, the material contained a very high percentage of silver — not pure silver, but close. It melts at very low temperature and requires great skill. If you stay too long with the flame, you burn the material and lose its properties. The color must never become red — it should remain a soft pink. That is one of the secrets.

Close to pure silver is more difficult than silver with brass. If someone is used to brazing brass at 700–800°C, almost pure silver is completely different. It requires sensitivity, manual precision, and experience.

Over time, materials have changed. High-silver alloys became very expensive and harder to find. Many manufacturers reduced the silver content and increased nickel or brass. Even today, we are fortunate to work with a supplier that still produces a very high–silver–content alloy that allows us to braze at around 600°C — which for me is ideal.

So, does a perfectly aesthetic weld guarantee greater longevity? Not necessarily.

The weld itself can be extremely strong — especially with TIG. But for steel bicycle frames, in my opinion, what matters most is protecting the integrity of the tube by limiting heat.

This is my belief. Others may disagree — and that is normal. In welding, as in many things in life, there are different schools of thought.

But for me, steel deserves respect. And respect means low temperature, patience, and control.

Saluti,

Renzo Formigli