Reinforcing the fixation points

After some testing of the frame once assembled, it was clear that the front fixation point over the pedal bracket, connecting the beams to the head tube and to the fork bracket was not strong enough. The front support is subjected to large stresses as it supports all the loading from the fork. Moreover, while pedaling there are alternating stresses left and right. The brazing joint I made was not strong enough for taking these localized stresses. The reason was that both cylinders, the down tube of the original frame and the 10mm tube, intersect each other over a very small area. On the other hand, the key to sound brazing joints are large areas of contact with a very small and controlled gap. With the current design, those factors were not secured; therefore, I needed to device a solution to increase the area of contact of the different components of the whole assembly.



I started by turning some reinforcing rings to be brazed to the cantilevered tube at each side, which in turn offer a generous lateral contact surface to the main tube of the frame. You can see below the boring of the internal hole to 10 mm. The internal diameter is important for the gap design to the inner tube for brazing. A gap of about 0.3mm is satisfactory.



Here is how the concept looked in the front fixation point. So far, so good. Detailed mitering of the lateral contact surface is not yet done.



All four reinforcing rings machined and ready.



The rear support reinforcement rings are brazed without major problem. I left the front support to the end, as it is the most loaded and critical, and I could benefit from the experience of brazing the rear support first.



Front support done.