Assertions that thinning lugs reduces stress risers and increases frame durability are repeated often enough by respected builders that I think there is probably some truth to them. This is from the
Spectrum Cycles website (Tom Kellogg and Jeff Duser).
Originally Posted by Spectrum Cycles website
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 also makes 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.