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Mitering tubes.
Beginning steps - deciding what you want to build.
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When I first started lurking on the framebuilders list, a thread was going around about tube mitering. People were discussing the right hole saws to use, and the best way to hold the tubes in a mill, and feed rates, and such forth. It was all a bit frightening for a newcomer. Tubes must be fitted together in such a way that there is maximum metal in contact. This is done by removing metal from the end of one tube so that it sits around the other. The tube end then looks like an open fish mouth. I found a way to do it which is relatively simple, very time consuming, and needs very few tools. First, you draw an outline of the miter on the tube to be mitered. This is easier than you'd think. There is a fantastic program on the web, called Tube Miter, which plots a picture on a flat piece of paper, which you wrap around the tube to mark your miter. Then clamp the tube in the workmate, and go to work with hacksaw and half-round file, and after a while you have a nice neat miter. As with everything, fitting all the bits together and making sure it coincides with the drawing works well. I mitered both ends of the down tube, and both ends of the top tube. I mitered one end of the seat tube. It's necessary to cut an additional miter at 90 degrees to the first in the down tube and seat tubes, where they would otherwise intersect in the bottom bracket shell. I just marked the tubes from the inside of the bottom bracket. Also important is to make sure the miters on either end of the top tub and down tubes are at the right angles relative to one another. I drew a line down each of my tubes before I started to act as a reference. Finally, I drilled 6mm holes in the head tube and seat tube, in the center of the space where the top tube and down tubes would end. This was to allow me to clean flux and other gunk out of the tubes after soldering.
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