this shot shows the welding clamp in position on the longeron.
just imagine you are welding the cluster I've suggested with the
pieces of wood.
the idea is to hold the longeron in place as the gas weld cools from
red heat. this prevents the slight shrinkage which typically causes
the bend in the longeron. it causes no harm to the weld but just
prevents the longeron bending.

This little gas welding aid was shown to me by an absolute master at
aircraft tig welding, my eccentric brother in law Graeme Stevens of
Brisbane in Queensland.

btw you never paint these since the gas flame is constantly playing
over it. it makes a useful gas welding practise exercise.

my thanks to veedubber for prompting me to post this.
Stealth Pilot

....and yes graeme voiced the opinion that my gas welding was quite the
worst he'd seen in ages. :-)