During the week, whenever I had a break from work, I managed to make progress on cleaning up and joining the lengths of steel.
First, I cut off the ugly accretions.
Then I cleaned off the ugly gas axe cuts by recutting with a 125 x 1 mm disk.
I find a large 9 inch angle grinder frightening and I do not have enough strength to control one accurately.
Instead I clamp a thick straight edge over every cut I want to make and use this as a guide while slicing with the 1 mm disk.
By Thursday I had cleaned up all the lengths as well as welding some approximately 400 mm lengths on to extend the main pieces.
By Friday evening I had cut 4 fishplates out of a length of 10 mm plate.
Saturday morning, I carefully stacked these four plates so that they were flush on all sides and ran some light spot welds across them.
While I had them as a stack of 4 I drilled in 4 pilots holes, separated the plates again, and then drilled 16 x 12 mm holes.
During the remainder of the day I welded these fish plates on to the ends of the beams ( a lot of bevel grinding needed).
Then I dragged the beams out on to our paved area, lined them up on some glutz and checked that the fish plates would bolt up happily.
The fish plates on the middle beam area only tacked so there is still scope to tweak their layout.
Tomorrow, if there is any time, I will finish welding the plates on the central piece.
After that I will hit the rust with a rotary brush, apply rust converter and start painting.
The central beam, however, will require some additonal fabrication work - it will have two short stub beams running 400 mm down the hallway to provide stability.