Terry is correct about the place the tube will bend. I have another side of the “funny car cage” that should take care of that.
The point being discussed is the importance of having the center lines of the tubes meet to eliminate the weak area. One side thought is that I plan to not have any tube meeting point aimed at my body! Terry, I would worry about creating other weak points by removing the meeting point with the addition of a short diagonal as the one tube is only off by 3/8 inch or so. And remember my pdf is on the side with the bar not meeting being the horizontal bar and the three upright vertical bars meeting. Willie, any thoughts on gussets?
You must also think about creating a shear area where only one bar is located in the middle of a tube. Remember a triangle has intersections of the rays at the corner not up a little from the end allowing a “tail or leg” to stick out as a support. The place where the tube will bend, or worse shear off, is just up the leg where the rays meet so when you move the meeting point to the end of the tube the sheer is also moved to a stronger location or past the end of the tube. I will post another pic after the next weekend of the diagonal tube meeting the floor and upright tube.
A side intrusion bar or a shoulder harness bar does not need to meet another tube at the center of the angle, vertex, where the angle ray lines meet because these tubes are not part of the support structure. However, you can use part of the support structure for a side intrusion bar or a shoulder harness bar and then meeting the vertex of the angle is important. Hmmm, head spinning yet?
Another consideration is where to place bracing and have it add needed strength rather than add weight and moving stress from a strong vertex to a weak area. I drew the cage and then checked for triangles. And then thought about what stresses the car will have in the event of not being on wheels. I did change a tube from my first sketch. This varies from Bonneville to sled pulling to Maxton to track days to drag racing to… Most salt cars end up on their top and do not strike an immovable barrier like a concrete wall or get hit by another high speed mass (fellow racer) so plan accordingly. McRat needs a slightly different cage in his truck than I do with added protection for the additional impact types that may occur in his different events.
Follow the rule book first and then add if needed. The cage specified in the rule book has been empirically tested and is good for what we are doing.
I am fortunate enough to have a certified welder in our team and I am still reading welding books as we work on the car. The comments posted are good about the different types of welding. Roll bar welding is near the max for tig and middle for mig, depending on machine so all comments can be correct.
My reading about welding brings up temperature being important and 90 degrees best with weakening at 55 degrees and below, gas choice, good quality wire from a major vendor creating a stronger weld than cheap wire, etc. Another point is how to weld tube intersections to eliminate warpage using tips found in ”Welders Handbook” by Richard Finch, page 38 and “Modern Welding Instructor’s Manual“ by William Bowditch, page 218.
I think this thread is going to result in better cages for all. Charles, join me in learning, again after a 25 year break, how to weld. I just got a setup for aluminum.
Geo
