Fortunat1 wrote:

I believe that you have to effectively have a full lap joint weld
between each outer tube and inner tube, AND the joint must be a
truncated cut and not just straight across in order to have sufficient
weld cross section since it's essential that the weld zone be much
stronger than the virgin metal up the tube.

The rosette welds done further up don't contribute that much strength
and are mostly (I believe) to prevent the inner tube from having an
unsupported length that allows "wiggling" of the inner tube in the
outer tube under stress. possibly leading to cracks in the main weld.



OK, I can buy all of that, but I don't know exactly what you mean by
truncated. Are you talking about the profile of the edges of the outer
tube, or do you mean the outer tube must be cut diaganally?


Look at it from a "stress riser" point of view.

A weld (I see what the problem is here - how to describe in words what
you are thinking in yer head)

Ok

If a welded tube is butted together with square cut ends (90 degree cut)
the weld will cause a sudden localized change in cross section - a
stress riser - something we try hard to avoid.

But lopping the tubes at 45 to 60 degrees spreads the "bump" in the
cross section of the weld across a longer distance.

Think of the weld bead as a "hard" spot. Angling the weld avoids having
a hard spot in a tiny localized area.


What John said about the rose on the inner tube is about what I recall.
Stabilize the inner tube and (again) avoid having the hard spot all
concentrated at the end of the inner sleeve (at the cluster).

FWIW?

Richard