Along with the wave of electronic components, there was a cultural aesthetic riptide which added the difficulty to streamline the outside of the bike: hide the wires. One advantage here is that the electronic signals no longer require straight lines or necessarily smooth curves to achieve the perfect response; although a kink wouldn’t be great either. While Shimano spent many extra hours streamlining ways to add the wires into the bars and stem, the frames also needed to change. Following this same line of thought, is an entirely new way to think about frame construction. The classes we present at UBI are not exempt, in fact, frequently our instructors are already on the front of that thought, querying; how can we bring this to our students?

Sometimes, it is not that easy. Those who have fabricated frames or taken a class with us before, already realize that not only does this mean imagining and researching the components; it means new standards, new jigs, and foolproof ways to repeat the process over and over without danger to students before rolling it out in our classes. Our current projects have included T47, flat mount disc brakes, and of course, Di2.

See the different sizes of vent hole? The smaller one is just to allow the fumes to exit, the larger, for internally routed Di2 wires.

First for Di2, we need new entry ports into the frame to accommodate for the smaller wires, and they can be located in new positions, but we don’t need to accommodate cable housing any longer. On the frames we fabricated for our new Di2 seminar, the entry port is on the top tube, so the wires can follow the rear brake cable to meet the frame (reducing the number of visible wires). It hooks a hard u-turn once inside the top tube and then pops into the head tube, through the head tube and into the downtube, where eventually it will meet with the Junction Box near the bottom bracket shell. This Junction Box will be where all four facets of the system will need to integrate; battery (inserted into the seat post via the Shimano adapters), front derailleur, rear derailleur, and shifting system.

Newer, larger, head tube vent holes to accommodate the internal wires.

With all these wires being run through the frame, the next big thing we have to think about as a frame builder, are the holes for the wires to get from one frame tube to the next. Typically vent holes can be quite small (sometimes just  1/8”), we just need to let fumes, water, and acid (from flux) escape. Now we have to increase the diameter to allow for wires to get through, and if you’ve ever strung together internal routing, bigger is better.

But this increases the need for a more exact vent hole. If your tube is 1” in diameter and the vent hole you’re trying to drill is ¾” that leaves a mere  1/8” on each side of the vent hole for the tube to sit, and for the heat to soak in while brazing or welding.  And that’s the vent hole at: the head tube / top tube junction, the head tube / down tube junction, the right chain stay to bottom bracket junction, and the seat tube / down tube / bottom bracket junction. 

Shimano's Junction B box still needs to be tucked into a tube to be truly internal.

One last thing to consider; where to tuck the B Junction Box, down tube or seat tube? Typically, this Junction Box will be tucked into the downtube. Therefore the wire from the battery (seat post) and from the front derailleur, as well as the wire from the rear derailleur, will all circumvent the bottom bracket prior to plugging in to the Junction Box.  Either way, the connecting hole to the bottom bracket shell needs to allow for a ¾” x ¼” x 1 ½” plastic box with 2 wires protruding from each side.

At UBI, we’ve solved these dilemmas (combined with imperfect student miters) by mapping out each vent hole very carefully after verifying the fit-up of the tubes and then drilling each vent hole as it needs to be drilled.

 Of course… you could just do SRAM Red eTap instead, and not drill any holes for the shifting at all, but that’s another article for another day.