Workshop Update: Bi Laminate Construction

Howdy folks. Things are busy busy busy over here. I ve got a few projects in various stages and mixing in the occasional repair job too. One of the main things I am working on  is a belt drive commuter fixed gear bike for Stephen in Los Angeles. This build is going to be a truly custom build by the time it is complete(which is hopefully sometime soon….). I don’t want to disclose all the details till I have the pics to back up the words, so I will post updates through out the build process.

The fork was done awhile back during my “fork party”(see post below). I ve now got the front triangle done, and Stephen has seen the pics and approves, so I can share it with y’all. The front triangle is whats called “bi-laminate” construction, its kinda a faux lug, though the word “faux” doesn’t do too much justice for the amount of work that goes into such a project.

From my understanding, bi-lam originates from post-war Britain and was pioneered by Claude Butler. It started primarily due to the lack of materials after the war. Originally the “lugs” would start out as a flat sheet of metal with a design cut out of it. After the frame was fillet brazed, the sheet would be wrapped around the tube and brazed in as well. It the gives the impression of a lug.

My process was a little different. I started of with piece of cro-moly tubing that would have a sleeve fit with its corresponding frame tube. I then drew out a design on to the tube and cut it out. I then brazed the sleeve to the tube, did this to all three tubes, then headed over to my buddy Watson’s, from Arundel Bikes, well equipped shop and turned down the material of the sleeve on his lathe. I then mitered the tubes as normal and then fillet brazed. Due to the extra long length of each lug, I was not too concerned about melting the filler inside the lug  while brazing the joints.

Though this process is not too common, when it is used, it really allows the individual builder quite a lot of creative freedom as they pretty much have to make the sleeves from scratch or heavily modify existing lugs. Some builders will place the lugs on the head tube. This helps reinforce the head tube from both heat distortion and from reaming material out for the head set. I chose to use a thicker walled head tube, and place the lugs on the top tube and down tube. Though I hate to admit it or be caught doing anything frivolous, this does serve more of an aesthetic purpose than any structural or functional concerns. Once the bike is painted the combination of the seamless fillet braze and sleeves on the top tube and down tube will make the  head tube and lugs appear as one piece.

The sleeve on the seat tube, however, does have more a functional purpose. It strengthens the tube from any heat distortion from brazing the seat stays and top tube. It also provides reinforcement from pressure from the seat stays taking force from the rear wheel. There is a reason for the extended seat mast, but I will share that with y’all later….The drilled circle theme was both for a little visual touch, but also for gauge for me to watch the filler metal flow in, down and around the tube. I then carried the circle motif onto the top and down tube lugs.

Though this was a perfect opportunity to cut some intricate design into some metal, and have the utmost respect for the talent and zen-like patience it takes to make “fancy lugs”, I am a “less is more” kinda dude and find the simplicity of a long point lug is extremely classy, elegant, and even timeless and chose that as general form of these lugs.

As I mentioned earlier, this is a belt drive frame, so my next step is designing and then finding a way to get some drop outs made. The design is coming along, but I ll hold off showing it off till its done.

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