A number of my bikes have been changed due to structral problems that have happened to them. The bikes in question are the Naboo and the Low Racer. One of the main problems that I have been running into on the Naboo was the mounting of the Bottom Bracket to the steerer tube. There is a great amount of stress in this area. The original mounting had the mitred, cut tube welded on the steerer tube There was no extra support material to help support this structure. Due to the tight fit and closeness of the joint, welding the entire joint was very difficult. Since a small gap was left, this left an area that could (and did sheer off). I needed a better way of getting it to fit in a more long term manner. I did the following make a stronger joint.
- A smaller piece of steel tubing was welded into same spot as the present current BB location. It was placed so that the BB could fit over the new support piece.
- The weld was put on to the inside of the support tube so the it would not interfer with the push-on fit of the BB.
- When the bottom bracket was put back into place, there was addition material for the weld wire to take hold on the bb attachment point. Extra care was taken also taken to fill in the gap area around the mounting point.
With the added hidden support tube in place, this should make the BB a much more relibile now.
The Low Racer recumbent is another bike that has run into some structural problems. The main problem with this one is main down tube that joins the seat/ drive train section to the steerer tube. The 1.5" thin wall tube was not up to the task of supporting the weight of the rider and the flexing of this section createed from the front mounted fairing. Although the first break took place on the upper section the main frame near the steerer tube last year, the bottom section broke near the seat base area this year. An additional support bar was needed to strengthen this area so overall strength frame was to be retained.
A 1" by 1" square steel tubing was place over the existing down tube. It was welded in at the bottom, middle and top areas There was some triming at the top and bottom to help in fine fitting this part into place. The end result is a stronger mid-section that is stiffer now. There was a little flex in the frame before but the bike much more rigid with the new support bar in place.
That's it for now. The lesson here is to really look at what you are doing it terms of your frame structure design and see how well it will hold up the the real world. The general rule of thumb is to over build so that there is less chance of things breaking.
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