Take-apart joints: attn Mark Stonich

[email hidden] (john riley) wrote in message
news:<[email hidden]>...

Quoted message said:

I have a folding Rans Wave with the tubes butted up against flat plates at the joint. It has
worked so far, but it hasn't seen all that much use. IIRC Mark has opined that he thinks the tubes
need some reinforcement if you do this.

Context is everything here;

I was talking about a thinwalled monotube, which is a completely different structure than a Wave.
Because of triangulation, your tubes are stressed primarily in tension or compression. Especially so
in the middle of the frame.

Imagine welding the end of a tube to a solidly mounted plate. Pushing or pulling the tube, with the
force applied parallel and concentric to the tube's axis will have little effect. You are stressing
all areas of the weld equally. This is the situation on a triangulated frame.

Now apply force at the end of the tube, at right angle to the tube's axis. To get failure you only
need to overstress the bit of the HAZ closest or furthest to you. This is the situation in a
monotube frame.

Quoted message said:

Any other opinions? What is it about this flat joint that would weaken the tubes more than any of
the other joints on a bike?

With a monotube the major joints are at the ends of the tube, where there is much less stress. A
little decrease in strength there is less of a problem than mid wheelbase where stress on the bottom
fibers of the tube is greatest.

Also, welding to a flat plate means the edge of the HAZ (usually the weakest part of the tube)
encircles the tube, on the shortest possible path. At no point on the edge of the HAZ is there
sounder metal adjacent.

Quoted message said:

I am always on the look-out for something simpler and cheaper than the S&S joints.

John Riley

OK, I get it. So as long as I stick with triangulated frames, I should be ok. As it turns out, it is
the same deal with S&S couplers, but I suspect for different reasons.

JR