This F-705 bulkhead is proving to be a lot more complicated than I first anticipated. It needs lots of parts fabricating from scratch. I think this is the most parts I’ve fabricated for one assembly.
I started off by making two spacers at 16.25″ long as per the plans. That was easy enough as the stock was the right thickness and width and just needed trimming to length. Next I fabricated the F-705K plates which again where the right thickness and width. However, as well as trimming to length they needed to be bent at 4 degrees lengthways. 4 degrees is a tiny amount of bend and it took me a while to find a good method. In the end I opted to clamp the strip to the workbench using the back riveting plate and then make the bend using the flat faced hand seamers.
Once that part was made it was time to make the F-705J stiffeners. Again this involved trimming them to size but, for the first time, I had no holes to act as a template. The plans give dimensions of where the holes should go so I carefully marked the part, punched it with the automatic punch and then drilled no. 40 first and then final sized it to number 30. That was the easy bit.
The next instruction is to clamp everything together and drill everything to the top channel. I think I used pretty much every clamp I had to get this lined up. This was particularly tricky because the angle must have a 1/8″ gap between it and the frame so I found some aluminium bar that was exactly the right thickness and clamped that in place before drilling the angle to the channel. The whole task was very meticulous and nerve rackingly tricky. But, with oodles of patience, and triple checking, twice(!) I finally drilled all the holes and cleco’d everything in place. Verdict: I’m pretty happy with the results considering how difficult this was.
The next task for this session was to assemble the F-705 bulkhead and match drill the F-705G brackets I made earlier this week. There is absolutely no guidance in the instructions or drawings on how to do this so it was all done by eye and experience. For example I noticed that the outer corner of the angle was interfering with it seating properly so I rounded the outer corner so it fit much better. Next I drew warning lines a 1/4″ in from the outer edges so I could see if the holes would be within edge distance limits. Finally I clamped everything together in every dimension and then drilled all the holes using the predrilled holes in the channel as a template. Once the holes in the brackets were all match drilled I drilled the slots for the canopy latches into the brackets too.
Lastly, I match drilled all holes that had not already been match drilled and gave the workshop a good tidy up.