For a long time, I have wanted to build my own bicycle frame from steel and lugs. I began accumulating tools and knowledge about how to do this. It has taken me a few months to feel comfortable proceeding with the project. There is a lot to write about this, but I will jot down a few things I think are important.
I bought the Paterak manual. This manual is pricy, and it is intended for professional framebuilders, but it has lots of valuable information in it. It comes with a few videos that show brazing.
There are many different camps, subcamps, and subsubcamps in bicycle construction. I have chosen steel (over aluminum, titanium, bamboo, and carbon fiber), brazing (over welding), lugs (over fillets), and silver (over brass). I spent some time visiting with framebuilders with a lot of experience. One even sold me a decent Columbus Cromor tubeset. He also sold me lugs, bottom bracket, and a bunch of scrap stuff to practice on.
I designed my frame to be a cyclocross frame. It is an amalgam of the Lemond Poprad and Bianchi Roger geometries.
I drew out the frame blueprint on large pieces of paper. I laid this blueprint on a flat table. I made the table by going to Home Depot, getting a very large level, and going through the bin of 24" x 48" 3/4" hardwood plywood sheets looking for the flattest one. I found one and brought it home. It sits on a stand supported at three points. The support of three points rather than four allows the board to lay on one plane. This is one thing I have noticed about machine work and framebuilding--it is all about geometry. Very cool. I also bought a piece of 1 x 4 oak at Home Depot. It is a nicely milled piece of wood--sharp corners and right angles, and cut it into blocks. I drilled holes in these blocks that are the diameter of the tubes--1.25" head tube, 1.25" seat tube and downtube, 1.00" top tube. Then I cut the blocks in half to make pillows on which to rest the tubes over the blueprint. The holes are all pretty precisely drilled on the same center because I did this on my mill/drill. Here the tubes are on the blocks (click to enlarge):
The tubes didn't fit into the lugs at first because the lugs and bottom bracket are relatively rough castings. So I had to work on these with files and the Dremel. Here is the bottom bracket after this reaming was complete. I am intentionally leaving the mating surfaces a bit rough so that the solder has more surface area on which to gain purchase.
Here are the down tube and seat tube in the bottom bracket after a very rough mitering job. I stuck the tubes into the bottom bracket and marked with a Sharpie where I should cut. Because these tubes are butted in specific ways, you need to cut one end rather than the other. For instance, I trimmed the top of the seat tube because the bottom has thicker walls for strength.
Here is the frame after rough mitering. I didn't realize that I had a long way to go.
I was particularly proud of how concentric the tubes were with my amateur flat table and pillow blocks. Here is a shot of how nicely the downtube can slide into the head tube. They are on the same center.
But once I started to do all of the finish mitering, I found that some of the tube junctions were off because one tube was slightly higher than the other. This is not the end of the world--many framebuilders will build each part of the frame and then bend it into alignment by hand before joining it to the rest of the frame. Distortion caused by the heat of brazing can knock off alignment, too. But I want to be as precise as possible. So I measured the height of the tube whose center was highest off the the plane, and made that the benchmark. Then I added sheets of paper under each pillow block and screwed them all onto the table. It took a few iterations before I got all of the blocks at the right altitude. But they are with in 2/1000ths of an inch now.
Because I do not want too braze on the wood table (probably could, but it would get smoky), I needed to figure out a way to preserve my perfect alignment when I take the frame and hang it in the bikes stand for brazing. Some people have metal fixtures that allow them to braze the whole thing while it is locked in alignment. But the old school way to do it is what I chose. I bough 6d (6 penny) nails at Home Depot. These nails are almost exactly the same diameter as a 3/32" drill bit. I mades sure that the frame was in perfect alignment and then drilled a hole at each junction through the lug and tube and then inserted a nail. This pins the joint in place. I checked with a straightedge to insure that the bottom bracket is perpendicular to both the downtube and the seat tube, and then drilled the holes for those junctions. I had to do two pins in the downtube-bottom bracket junction to hold it in alignment. Now the frame is pretty darned solid and can be moved around without losing alignment. I am not under the delusion that this will prevent minor alignment problems, butI can clear those up by "cold-setting" or bending them into alignment after brazing.
