Used the clamped on engine-mount mountings from yesterday as guides to drill the jig to 3/8" at the four corners using the pillar drill. Then fastened the engine-mount mountings onto the jig and clamped this to the fuselage. The use of the jig ensured that the engine-mount mountings are exactly aligned with the fuslage datum both horizontally and vertically. Tack welded the engine-mount mountings in place in the fuselage and then removed the jig to final weld them and the firewall diagonal into place.
Replacing the jig afterwards confirmed that nothing had moved and measurements proved that the two diagonals across the engine mounts
were accurate within measuring tolerances. Cut four 1.5" lengths of 3/4" * 0.156" tubing that will form the corners of the engine mount itself and welded these to 1-1/2" washers.
Used the clamped on engine-mount mountings from yesterday as guides to drill the jig to 3/8" at the four corners using the pillar drill. Then fastened the engine-mount mountings onto the jig and clamped this to the fuselage. The use of the jig ensured that the engine-mount mountings are exactly aligned with the fuslage datum both horizontally and vertically. Tack welded the engine-mount mountings in place in the fuselage and then removed the jig to final weld them and the firewall diagonal into place. 
Replacing the jig afterwards confirmed that nothing had moved and measurements proved that the two diagonals across the engine mounts
were accurate within measuring tolerances. Cut four 1.5" lengths of 3/4" * 0.156" tubing that will form the corners of the engine mount itself and welded these to 1-1/2" washers.
