Wednesday, January 19, 2011

Steel 29er in progress

I put up lots of photos of raw welded frames but I seldom have photos of the 'fit-up' stage. These two photos show the mitered union og the two tubes in the pre-weld state. I show this to illustrate the need for a very uniform and tight fit between the tubes. If there are any gaps there will be distortion when the weld cools. In theory, the unitform tight miter will yeild a stronger and better aligned joint. I always try for the best fit up possible. When a frame is lugged, the fit is hidden inside the lug , making it difficult to know if the fit-up was good. With a welded bike there is nowhere to hide-everything is out in the open. This is why I am puzzled why some folks consider welding less of a skill than brazing with lugs. No doubt, there are less steps with a welded bike but there is the need for precision and the margin for error is tiny.
In these photos the front triangle portion of the frame is in two sub-asseblies: Top and head tube, down and seat tube ( to B.B. shell ). This is a critical stage where if done correctly, the frame can wind up with proper angles and no twist. If the inside angles are off a little, there can be all sorts of issues with alignment, steering and stability. I take my time at this critical juncture as I have learned from many years of doing this-hurry this part and you'll wind up with a nice piece of scrap !

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