I find it amazing that a method of building bicycles can be around for over a 100 years, and become lost to a new generation in ten years or so.
Since the bicycle’s invention in the late 1800s the traditional way to join steel tubes to make a bicycle frame was by melting brass into a lugged joint. Similar in a way to a plumber joining copper pipe by sliding the pipe into a pipefitting, heating, and filling the joint with solder.
Brazing, as it is known, done at a higher temperature and the resulting joint is much stronger. Early lugs were in fact pipefittings; these were heavy steel sand castings, cut square at the edges, and machined on the inside to fit the tube.
As steel tubing for bicycles became thinner and lighter, it was found the tube would sometimes break at the edge of the lug. This was because the lug was far stronger than the tube.
In any structure, if you make a joint far stronger than the parent material, the material will fail during stress, immediately adjacent to the joint. Framebuilders started filing the lugs thinner to bring the strength closer to that of the tube. For the same reason, they also started cutting the lugs into fancy shapes to eliminate the square edge of the lug.
By the 1950s the cutting and filing of lugs became the way a framebuilder would express his art and individuality. Hetchins (Left.) were one of the first to take this art to extremes.
By the 1960s and 1970s, fancy lugwork became too costly and lugs stamped from sheet steel and welded, became available. The top picture is a set of pressed steel lugs that I prepared during the 1970s, with some custom shaping a cutout work.
By the 1980s “Investment” cast lugs became available. A method developed for the aircraft industry, investment casting was achieved by first hand making a lug. From this “pattern” lug a simple plaster mould was made.
A lug made of wax was cast in the plaster mold; this in turn was coated in a ceramic material and fired in an oven. The firing hardened the ceramic coating and at the same time melted the wax from inside, leaving a void the perfect shape of a lug.
Molten steel was poured into the mold, and when cooled the ceramic mold had to be broken to remove the finished lug, hence the name, “Investment” casting. An expensive process, but the finished lug was near perfect, the tubes fit with no machining required; very little filing required from the framebuilder. Lugs, bottom bracket shells, and fork crowns are made this way.
Traditionally frames were never welded. Not because welding was not strong enough but rather the heat required to weld weakened the parent material adjacent to the weld. By the 1980s welding technology had advanced to where it could have been used to build lightweight frames. However, at the time customers, connoisseurs of the lugged frame would not accept it.
This changed during the “death” of the road bike in the early 1990s. Mountain bike manufactures could get away with the quicker and cheaper welding process, because the MTB was new and there were not the old standards, and traditions to break down. There was a whole new generation who grew up with welded BMX bikes.
When the road bike was reborn, sadly, for some of us it was an ugly bastard. Its gene pool contaminated by MTB and BMX, the beauty, style and class bred out of it. A well, that is I suppose the price we pay for progress.