WHY WE STILL USE LUGS
Our steel frames are lugged for two reasons. Lugs are stronger and lugs are beautiful. Did we mention that Lugs are stronger? Almost all mass-production steel frames produced today utilize cost-effective tig welding to join tubes. This prompts a question: why do we still use silver soldered lugged joining? There are two basic answers. First, properly fitted and soldered lugged joints are considerably stronger than joints created any other way. Second, they give us and other traditional builders a way of showing off. We can demonstrate, not only our soldering skill, but also how we believe a frame's details should appear.
ON STRENGTH
In the late '80s, a team of scientists in the UC Davis engineering department undertook an in-depth look at the relative strengths of various steel joining techniques at the request of "Bicycle Guide" magazine. The three top frame builders associated with the three primary joining techniques were asked to supply joining samples using tubing supplied to the builders from the same mill run. Tom Ritchie provided the fillet-brazed samples, tig-welding was done by Gary Helfrich, and the silver soldered lugged samples were done by Spectrum's Jeff Duser. The samples were fatigue tested, in some cases to failure. In most cases, the joints did not fail. More often, the tubes failed at or near the joint. The team's study involved microscopic analysis of the crystal structure of joining zones, heat effected zones and failure sites. They concluded that all three joining techniques, done properly, are clearly of sufficient strength for the purpose of bicycle frame construction. The different results obtained from the samples resulted primarily in the heat-affected areas of the tubes themselves. Not surprisingly, the tubes that were soldered turned out to be stronger than the tubes that were welded or brazed. So, what does this mean in the real world? Frames built with silver soldered lugs will last longer than those that are fillet brazed and considerably longer than those that are welded. However, for most of our customers, the real practical difference is that lugged frames hold up in crashes better, and when it becomes necessary, they are much easier to repair.
ON MODERN AIR HARDENING TUNING
The latest generation of air-hardening steel tubing used by top quality welding frame builders was not available at the time of the UC Davis study. We at Spectrum expect that this tubing, when in the hands of master builders, is more reliable than the welded joints and tubes tested at UC Davis but still less strong than lugged joints.