Besides the lugs, the other metal bits on this frame are the brake bridge and the screw bosses for the water bottle holder. For the brake bridge I started with some 1/2″ thick aluminum plate. I sketched a shape on cardboard, traced that onto the metal, and cut it out roughly with a bandsaw.
The brake I am using has a nut that is meant to be countersunk (otherwise the bolt isn’t long enough). I just did this with a drill bit, which seems to work alright, even though the bottom of the counterbore is conical, not flat.
What followed was a lot of Dremel work. I discovered my love for burrs like this:
Its kind of like using a handheld end mill, and you can actually remove a considerable amount of material with each pass, so its much faster work than you would expect. After the rough shaping with the burr, I did a lot of hand sanding with sand paper to get softer edges.
Here it is after a layer of hemp and some sanding:
To get the screw bosses for the bottle holder I cut up my original metal frame with the screw bosses so that I would have a big flange to glue it to the bamboo. I used the same Dremel burr to shape these flanges so they fit well to the tube and tapered nicely on the edge.
To fit these on the frame itself, I just had to drill some holes to clear the threaded insert and apply epoxy. They don’t seem to take that much load, so hopefully this is enough to hold them in over time.