I did it once, on a finished frame, by drilling a hole in the top tube at either end. the holes have to be drilled at an angle so that the hole ends up being elliptically shaped instead of round. then i inserted a stainless steel tube through the front hole and pulled it out the back hole. then, i silver brazed it in place, filed it flush with the top tube, and brazed a little reinforcing plate over the joint. i think i used brake bridge reinforcing plates that you can buy already made, they're nice oval shaped and have a hole already in them. anyway, using a stainless tube brazed in place keeps your top tube sealed off from the rain. however, like matt houle said, it would be WAY easier to do it before brazing the entire frame together; it was a real bear for me to get the stainless tube into a completed frame. but when it's done it looks really nice, well worth the trouble i think
From: Dave Wilkins
I use brass tubing from the hobby shop, sized for generous fit for the NEXT larger size cable housing that will be used. That way, if the thin (also lightweight) brass tubing gets a dent in it, the housing will still pass.
If it doesn't dent, maybe somebody later can put some larger cable thru there.
Like Matt Houle mentioned, it's better to install the internal routing before building the frame. So after laying out the in/out locations for the internal, I'll chuck up a drill bit that is slightly smaller than the O.D., then drill a hole into the tube. To keep from drilling thru both sides of the tube, I'll put a stop on the drill bit. (just slide a short length of steel tubing over the drill bit, leaving only a 1/4" showing)
Then with a pneumatic die grinder with a carbide bit, cut the drilled holes to a long horizontal oval. Make these oval shaped holes the same shape as the brass tubing as it enters/exits the tube at a very shallow angle.
Next file the oval holes until you can pass the tubing into the frame tube. As you slide it in, because the tubing is very thin walled and soft, it will hit the far side of the top tube and will take on a curve. This curve is what will help to guide the brass tubing out of the exit point. When you get the brass tube to where you can grab it with a pair of needle-nose pliers, just grab it and pull it on out.
Next, clean up and silverbraze; cut the excess brass tubing off and file.
Look thru the frame tube from the end, and see if the internal tube is touching the far wall of the frame tube. If it is close, when you hit a bump, it will rattle. I learned this on my pride and joy first frame which I still ride. But it is a bitch to fix later if you don't reach up in there with something like a piece of wood like 1/4x3/4 trim and bend the internal
till it's centered.
Be sure and silver braze (low temp) because these can end outside of a butted portion of a tube. That's some thin stuff...
Now you guys who work in framebuilding shops day in and day out may chuckle, knowing of some better way to do this, but I have no mill, lathe, etc. I just use basic tools in my garage. My daddy used to say that if I inherited a cathouse, I'd try to run it by hand...
Dave Wilkins Wrote:
'Be sure and silver braze (low temp) because these can end outside of a butted portion of a tube. That's some thin stuff...'
This is the main reason I will not use this method of cable routing. If done correctly, the inlet and outlet should be in the butt of the tube, otherwise, they can be prone to cracking at the holes. Miyata had an enormous problem with this on thier team, 916, 912, and 712 frames for a couple years. I worked at a shop that had about thirty of these frames with cracked top tubes left from warranty replacements.
So be careful where you're drilling those holes, and how thin your top tube is.
Thursday, 29 January 2009