Finally the main fuselage structure is welded so it's on to more interesting tasks but first a few comments on technique. I found that using a 1/16" ceriated tungsten with a number 4 gas nozzle gave best access into the tight spaces in the complex clusters. In many places new thin wall (0.028") tube is welded to either much thicker tube or existing welds. In this case it is was necessary to run a bead of weld metal along the edge of the thin tube to stop it burning away when using the higher currents needed to establish the weld pool in the thicker material. Currents used ranged from 15 amps for running a bead on the edge of 0.028" tube up to 40 amps for closing the filet in an acute angle between two sections of 0.049" tubing. Other currents were 18-21 amps for 0.028" tubing, 22-25 amps for welding 0.035" tubing and 30-35 amps for 0.049". First new task was to create the horizontal stabiliser (HS) spar carry through. 
This is formed using a 3ft length of 1-1/8" 0.058" tubing with a centre section reinforced using 18" of 1" * 0.035" tubing inserted inside. This was secured in place using a single rosette weld. This whole assembly then has to be squashed to be a tight fit in the 1-1/4" 0.035" tubing used for the HS spar. This was done in the vice section by section using a ring of the HS spar material as a gauge. Not an easy task, the 4" vice needed a 4ft lever arm to provide sufficient force to squash the tube as required. The spar carry through was then test fit for alignment both horizontally and for and aft. To do this the fuselage was re-attached to the building board with the lower longerons that form the datum parallel to the board and the centre line aligned. A digital spirit level reading to 0.1 degree was used to get everything exact. Next the fin spar was fabricated. This also uses the 1-1/4" 0.035" tubing but the top section is then welded onto some 3/4" tubing to provide the taper in section of the fin. This is done by cutting V sections out of the larger tubing over a 1-1/2" length and then bending them together around the thinned tube. The rear of the longerons were then shaped to accept the fin spar ensuring this was correctly aligned. Final job today was to fabricate and weld in place the tail spring support tubing. This now needs drilling and a nut welding to the top of it to allow the securing bolt to be removed with no access once the fuselage is covered.
