After matchdrilling the armrests, I removed the side skins again and deburred the edges. Usually I don't make pictures of this, but in this case, I want to draw everyones attention on the importance of carefully deburring the notches on the F770 side skins. Especially where the conical bend has to be made. The bend at that point is very sharp at 90° and many websites and builders have reported cracks in the relief notch.
Take your time, use keyfiles and sandingpaper to smoothen notches. Here's a picture of how smooth mine was.
Same story on the notches where the rear spar bars for the wing attach.
After deburring, it was time to start forming the conical bend in the F770 ears. This is the place where the square cabin/baggage side of the fuselage transitions in the conical shape of the tail in the aft fuselage. First clamped the side skin on the bend line using the backrivet plate.
This is how I positioned the notch for the sharp bend.
I was luckyt. Hugo who's building an RV-9 still had his angle so I could just re-use it without needing to drill the angle first. I attached the piece of angle and clecoed every hole as mentioned in the manual and used a grip to start the bend. Making the bend requires a rolling motion while pressing the skin downwards to avoid making a line mark at the backrivetting plate. At the same time, push with the thumb against the inside at the sharp bend. You will need quite some force to have the 90° sharp bend but don't overstress things. Go slow, pushing it a bit at a time.
You are done when the rear end makes a nice curve and the side stands up at 90°.
Here you can see how sharp the bend actually will get on the front side. That's where most cracks occur.
If you have a crack, don't panic. stop drill at the end of the crack and use keyfiles to smoothen things out. Many builders have this.
Another look after the first matching attempt. It needed some more to be perfect.
After the second bending attempt, things fitted perfectly.
And what 's better... no cracks ! I was very pleased with this result.
Time for the other F770 skin on the passenger side
Same process of bending on the backrivet plate bend line. I actually reused the angle using the same holes and just drilling two extra ones.
Starting bending process
Me at work, with the bend near completion. I got the second one ready at the first attempt.
Passenger side installed.
And again, perfect bend, no cracks.
From the inside, after removing the baggage skins, I noticed that the tabs on F706 will need some adjusting to butt nicely against the bend skin. I will do that fine tuning in a next session.
And here is the picture with both side skins bend and installed. It's very nice to see the assembly without those ears sticking out.
Overall very pleased about this job that I was a bit scared about but that turned out to be a no-brainer in the end.