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.

On Beauty
All high-end lugged frames today use investment cast lugs and bottom bracket shells.  For practical purposes, the lugs are all of equal quality.  Most American frame builders use Henry James cast components because of their availability in a variety of sizes and angles.  With so many builders using the same lugs, how much difference can there be between the various builders’ lug work?  As it turns out, the differences are substantial.  Depending on how much time a builder is willing to spend on their lugs, the appearance and strength of the final product using the same frame components can vary a great deal.  We typically spend hours on our lugs, finishing them as preparation for building your custom steel frames. However, the design of the UC Davis metal joining study did not allow us to finish our lug-work. Because of this, the joints tested in the study, though clearly stronger than welded joints, were not as strong as the ones used in our production frames. 

So how does finishing the lugs add strength? 
Good question. Most cast lugs have relatively thick edges.  This thickness causes a "stress riser" or a point where stresses are concentrated where the structure of the frame suddenly becomes thicker at the lug.  This stress riser is exacerbated by the relative thinness of modern tubing.  These weak points can be nearly eliminated through lug finishing. For many years, we have taken the time to remove close to 30% of the material from the lugs we use before we even begin the frame assembly process.  Thinning the lug wall significantly reduces localized stress and frame weakness and increases durability. As an added bonus, lug work alsomakes them appear cleaner and more delicate when assembled and painted.  And while almost anyone can solder lugs to a crisp edge, the difficulty lies in the finishing of the lug’s contours. Because of their shape, the contours of the surface of the lug are much more difficult to perfect. Here is where we excel. Look at our lug work and see the difference Spectrum makes. The cleanness, sharpness, and uniformity of our lugs are a reflection of our art, our experience, and our passion for perfection.  

On the Advantages of Welding
There are real advantages to welded frames.  First, assuming that the tubing used is the same, welded frames can be lighter than lugged frames.  Though the weight penalty of lugs is only a couple of ounces, we have to admit that lugged frames are still heavier.  Second, welded frames are MUCH less expensive to build.  Not only do high quality lugs cost a lot more than a welding rod, but finishing them properly takes many more hours on each frame.  Essentially, there is no finishing time spent on welds.  Third, building fully custom frames in unusual sizes and geometries is easier as the builder does not have to find, modify or create custom lugs.  Surprisingly, lugged, soldered joints are more exacting on the builder and therefore, more time and care must be spent on the fit-up of lugged frames.  Only those with a complete commitment to the highest standards of steel construction and frame appearance would take the time and energy to continue working with lugs.

On Lugs and Tandems
Since no one makes tandem lugs in the sizes and angles that we need, we make our own.  Talk about taking too much time!  We actually make, from scratch, all the lugs that are required to construct our tandems.  Is this an efficient method of construction?  No way.  Is it a stronger and more beautiful method of building a custom tandem?  Absolutely.  It's all we need to know (and its also the reason we can only do one tandem a year.