Adding braze-ons to frames

Adding braze-ons to a frame; All the evidence points to this being a significant factor in the robustness of the frame. Done poorly, and you could unwittingly undermine the structural integrity of the frame, make it significantly less robust and far more prone to premature fatigue-failure. Considering that a fatigue crack is the main way that a bike frame can fail (if not crashed), then this should be the MAIN focus of design thinking. It certainly is my preoccupation. 

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As with so many aspects of bicycle frames, many things are not so simple as they first appear. It is known that brazing one spot causes heat shrinkage, which is the exact same process used in old-school panel beating to intentionally cause distortion, to pull out a dent. This is why experienced framebuilders try to evenly heat all around a tube when fitting a braze-on, to try and minimise the shrinkage and hence distortion of the tube. They do this on every aspect of their frame build. If you have ever soldered on multiple sets of braze-ons along a tube, you will see that it can put a significantly curve into the tube. While that may be annoying or grate with your sense of aesthetics, the real issue is that locked-in tension in a tube has a definite impact on the long-term durability of the frame. The less locked-in distortion in the bike frame, the lower the initial levels of stress in the frame material, the more resistant the frame is at the "stress risers" (in this case the added braze-ons) to premature failure by metal-fatigue. This is not something that can be dismissed. Why? Because the main way that a bike frame fails in normal use is by fatigue failure. It is the attention to this sort of detail that is the difference between a master framebuilder, and a novice. You have made useful clamps, but you don't seem to have consulted experienced framebuilders in developing your design. If your clamps cradled the tube at the underside a couple of inches/50mm each side of the braze-on, then there would be enough clearance to get the flame in all around the tube to achieve an even heating, even heat-expansion, and absolutely minimise distortion due to uneven heating. Sorry to put a damper on your efforts. Knowledge is a wonderful thing. I am a full-time framebuilder and have some engineering knowledge too.

 

If you really want to dive in deep, locked-in tension in the tube material raises the level of stress in it, taking it closer to the fatigue-limit of that material even before flexing of that material begins. It is the flexing of the material in use that can take you over the fatigue-limit (the level of stress) of that material, and once you exceed those, fatigue cracks can develop. So instead of starting at near-zero levels of stress, locked-in tension has added perhaps 10-20% to the levels of stress already, making it far easier to exceed.

 

It is a thing. https://www.efatigue.com/training/Chapter_8.pdf