Other than a weight consideration, what concern is there with replacing a
typical fuselage tube cluster (all legs in the same geometric plane) with a
half circle plate where the slotted end legs are slide onto and then welded?

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Dear Dick,

In simple terms, the reason for NOT using the method you've suggested has to do
with stress (or load) concentration.

Maximum stress is said to appear in the 'outer-most fiber of the material,'
meaning on the surface of the tubing, not its center. The accepted method of
making a joint provides a continuous load-path between the outer-most fibers of
the members making up the cluster.

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With regard to the tedious task of fitting tubes to be welded, the tedium is
usually in inverse proportion to your tooling & experience. First off, the
tubes do not have to be a zero-zero fit. Indeed, there MUST be some gap,
otherwise you'll end up with a distorted cluster. Secondly, when a smaller
tube intersects with one (or more) of larger diameter, the fishmouth is little
more than a minor amount of scalloping. Finally, step-drills and a few
simply-made jigs will allow you to fabricate most of your fitted-ends on the
drill press, or on the lathe using milling cutters. The benefit of the latter
methods are more significant than they may appear because most structures of
welded steel tubing are symmetrical; such set-ups make it quite easy to produce
two identical pieces.

As with all of the manual arts, producing a nice cluster is largely the product
of practice. The use of mild steel tubing, such ERW, or even EMT with the
galvanizing removed, allows you to practice without going bankrupt buying
4130.

-R.S.Hoover