Tuesday, October 09, 2007


Not building frames full time, it can sometimes be hard to get into a rhythm of work. Lately, however, thats coming easier - leading to more progress, faster.

No pix yet, but tonight I finished the penultimate miter in the main triangle. After fitting up in the jig, I'll miter the bottom of the down tube. The rest are all done based on measurements from BikeCad and either miter templates provided by same, or scribing the profile of the inside of a lug. Anyhow, a test fit up looks good so we're almost ready to jig.

After the miters, it's important to take care of any fittings that go on the tubes. In this case, that means H2O mounts on the seat and down tubes, and a brake casing tunnel in the bottom of the top tube. The H2O mounts are pretty simple. Measure, mark, drill a pilot hole, drill out one size larger, then drill the final hole. A little clean up with a deburer, file and sandpaper and they're ready to prep for brazing.

The tunnel is a bit more work. First a mark the tube where I want to entrance and exit to be. These are approximate locations. Then its a similar process to the H2O mounts to drill holes - only this time there are more bits involved because the holes are bigger. Then its time to cut a length of brake line - this needs to be longer than the distance between the holes. Using a tube bender, I tilt each end about 45 degrees. The bends are slightly closer together than the holes in the top tube - so that the tunnel will stand away from the walls of the top tube once its brazed in place.

Next comes a large (12" I think) bastard cut round file. I use this holding it with two hands and cutting with the last 6" or less of the file. Using this I can elongate the hole s in the top tube. With a bit of back and forth to test fitting, the holes get finished off and the ends of the tunnel shortened until I can just pop it into place. Then it's time to pop it out of place so we can prep for brazing.

All three tubes spent some time in hot water with Wisk to remove any cutting oil left over from drilling holes. Then a dip in a degreaser just to make sure all is well. After this, I check that the edges of the holes are clean of burrs. Finally, the tubes get sanded with 80 grit on the inside and outside. The inside can be a bit of a trick to sand. I ended up making a flap sander for this purpose,. It's a piece of copper tube about 3/8" in diameter. One end has a slit cut in with a hacksaw. Then this was squeezed part way closed. Into the slit go pieces of sandpaper. Usually, I pull a 3" strip off a roll of 2" wide paper. This piece gets split lengthwise, and the to pieces are placed back to back - then shoved into the slit. The back to back thing makes sure that a rough side always faces the tube, no matter how the paper is put into the tube.

Anyhow, this gets chucked into my portable drill and shoved up the tube. Zing! The inside gets clean.

Then its time to flux everything up. I used Freddy's Stainless Light tonight. It was a little dry, so water was added before zapping in the microwave. The heat usually makes it easier to spread onto the tubes, and have it stick. I like the flux to have the consistency of slightly loose mashed potatoes. Done right, not to much falls off in the application process - and what stays there drys onto the tube if its allowed to sit for a little while. This makes it easier to keep the flux where I want it once the torch starts heating the tubes.

The H2O mounts are surrounded by decorative reinforcers. I try to get these straight before the flux drys. Its much easier this way than trying to poke them into position after things are heated up. Using a small tip and a soft but medium to large flame, I warm the area until the flux starts melting. As the flux gets clear, its time to add silver. I start by pointing at the actual threaded mount, and applying silver to the edge of its flange on top of the reinforcer. I point the tip of the flame into the threads (which have been fluxed) to draw this silver around the mount and down into the tube.

I don't like to apply too much filler here, because its easy to leave a glob on top of the reinforcer while pulling silver around the bottom. So I then apply filler first to the edge of one end of the reinforcer, and then to the other end. The end of the filler wire gets touched up against the edge of the reinforcer that is closet to me, while I direct the flame the other side of the reinforcer. This pulls the silver from the point of contact, under the reinforcer, to the far side. A little waving of the torch makes sure that silver is making it to the side points of the reinforcer. The same process is used at the other, end, but less filler is necessary because the first step filled more than half of the reinforcer. At this point, its important to look to see if there are gaps, globs, or other issues than can be best cleaned up now while the joint is hot. On both tubes, things looked great, so it was time to move on.

For the H2O mounts, I used a 56% Silver alloy. This gets very wet when heated and fits into small places well. For the brake casing tunnel, I use something called Filet Pro, which is a special formulation (I think high nickel content) for making silver based filets. It will wet out and I can pull it into tight places, but this takes work. On the other hand, it has a relatively wide band of temperatures at which it is plastic. And if the tubes aren't over heated, its possible to set a 3/8-1/2 inch length down and melt it a bit at a time by moving the flame around. Where the fit is tight, more heat pulls the filler through. Where a filet is needed, less heat is applied to the filler. But, where the filler needs to pull up on to the exiting tunnel, heat on the tunnel with an occasional dip onto the filler (to soften it up) pulls the edge right up. The net of this is the filler can vary from internal to filet and back as it works around the tunnel.

Don't get me wrong, file work will be necessary tomorrow to dress up the tunnel to tube transition - but it will be much easier than if there was a large filet all the way around.

Well, that's all I got done today. Well the above and soaking the flux off the tubes. So tomorrow I'll inspect my work and do any necessary filing. Then it will be time to get out the jig. The breathing holes need to be drilled in the head and seat tubes. Then test the fit up of tubes and lugs in the jig. If all is well, the tubes can be preped and fluxed and then it will be on to brazing. So there should be lots to report on in the next few days.


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