With a 1 5/8 OD, my bicycle's head tube is large. With a 1 1/8 OD, my fork is medium, I think. Or large. The line tangent the fork steerer tube exits the head tube defining about 92 degrees of chord.
Two cable guides are to be fitted to the head tube. Each will be mitered to about 46 degrees. Each will be drilled to about 5/64 or 2mm. Each will be counterbored a little less than 1/4 inch for the sheathing surrounding the wire, which will go from one guide around the steerer to the other, both being actuated by brake splitters and my brake levers have locks. All so I can park my bicycle without leaning against something, and on tilted terrain, and to make repairs. Weight in the front baskets lifts the rear wheel off the ground using the double legged center stand, usually used for tandems.
The mitered face of each cable guide will be filed to 1 5/8 radius with a half round file I have that fits that curve well, then sanded to the head tube with silcon carbide paper. They'll be brazed in place, almost in line, then the head tube will be drilled through the 5/64 inch hole to let the cable though. With the cables in a straight line, there shouldn't be any side force on the steerer, which headset bearings aren't designed for. Tension on the two cables will lock the tube when the brakes are locked.
Here's how I intend to manufacture the cable guides:
Hacksaw the sheared end off of the 5/16 rod I bought at Home Depot. Hacksaw off another 1 1/2 inches. Position less than 3/4 inch inside the drill press chuck. Sand a cross grain pattern on the rod. Flip the rod and sand the other end. Position 1/8 inch of rod outside the chuck. Part off a little disc with the hacksaw, leaving a circular pattern on one end. Position 1 5/16 inch of rod inside the chuck. Part off the rest of the rod, leaving both ends circular. Deburr on the drill press with a fine file. Resand if necessary. I figured do it first while the rod was longer. Clamp the rod in the angle vise on center, at 45 degrees tilt.. Fit a few screws in the rear holes I drilled and tapped in my drill press base. Mount the saw blade and arbor in the chuck. Support the head near the right level with the accessory table fitting. Run the head over to the right until the angle vise, against the screws, lines up the rod at saw height to the center of rotation along a line down the center of the vise. Adjust the saw height and saw the rod. Start the recess on the stub with a round file, not too deep. Finish the recess with the file that matches. Deburr the filing. File the other stub. Sand the stubs against the head tube, not too much. Set up the Unimat One to run a high speed 1 1/4 cup wheel against the work rotating freely in the three jaw chuck I wrote about, which comes with an MT3 arbor I don't need, but is threaded for the Unimat One. Chuck a stub. Start up the cup wheel and either rotate the stub against it, or allow the wheel to spin the work. Feed the cup wheel across the face of the part. Do the other stub. Set up either the graver support or the lathe tool to face, with the reduction gear. Pick up the work at about 5/64 diameter and get a stable groove started on center. Move the groove inward to produce a recess. Set up the tailstock. Drill 5/64 through. Drill stepwise to about 7/64 for the casing, just shy of the miter, about 1/2 inch.. Drill or ream 1/4 if needed. Deburr the drilled holes and inspect. Do the other stub.
After this we braze, and I am not sure I have enough heat. I have two 3/4 inch diameter flame propane torches and two MAPP gas cannisters. That should do.
It helps me a lot to write this out. Thanks for reading it. I'm going to print it and take it over to guide me. I like to know I can finish before I start.
My physics project at NVCC: Google Groups, then "dgoncz" and some of: ultracapacitor bicycle fluorescent flywheel inverter