When to perform F-770 conical bend (and other bend questions)?

So I've just assembled my aft and center fuselage assemblies, and it's now time to install the F-770 and perform the conical bend. According to Van's instructions, you install the F-770, modify the F-623 for the side step (if you're installing one, which I'm not), bend/twist the longerons to final shape, and fit and drill the arm rests. They then have you remove the F-770 skins and perform the conical bends, then re-install and match drill to the remainder of the fuselage.
I guess my question is, can I just perform the conical bend before I install the F-770 on the fuselage for the first time, given that I'm not installing the step?
Secondly, if I clamp the skin down to the table with some heavy angle or a back rivet plate, should I have the edge of the plate/angle running right through the center of the relief notch, or should I have it offset slightly (and by how much). The reason I ask, is that I notice when I bend in my brake, I need to offset slightly (depending on material thickness) to get the center of the bend exactly where I want it).
Finally, are you better off putting the angle on the outside or inside of the curve? I noticed that in Van's photographs in the manual, they cleco the angle on the inside of the curve, as does Larry in his post below, however I noticed that on Ethan's site, he has the angle on the outside of the curve, which would allow you to "push" rather than pulling on the clecos. My concern with this is that pushing rather than pulling may reduce the curve radius at the relief notch end, and thus increase your chances of cracks. Is there a clear winner on this one?
Ethan's solution:
https://rv-7construction.com/tag/conical-bend/
Larry's solution:
http://www.vansairforce.com/community/showthread.php?t=120747&page=5

I'm nervous as **** about performing this conical bend, so I think I will open the relief notch up to 5/32" or so to reduce the chances of a crack. Sorry for all the questions, however I may as well be ordering solid gold for the price it would cost to get a replacement skin shipped down here.

Cheers,
Tom.

try and get it in one motion, this stuff does not like to bend back and forth, work hardens and cracks easy.

Crack

bret said:

try and get it in one motion, this stuff does not like to bend back and forth, work hardens and cracks easy.

Click to expand...

What Bret said.
Debur the corner where the bend is sharp. Bend in one pass. If you need help, have another pair of hands ready so the bent corner doesn't relax until you're satisfied with the bend.
Remember the tight bend is almost 90 degrees. The soft bend is a smooth curve.
Take it a little past so it relaxes to the position you want.
Radius the bending angle so it doesn't leave a sharp crease.

Thanks guys. Good call on the rounding the edge of the angle you are fixing it to the table with. I guess this means I'm not using my backing plate for this purpose.
Tom.

Bend

tgmillso said:

Thanks guys. Good call on the rounding the edge of the angle you are fixing it to the table with. I guess this means I'm not using my backing plate for this purpose.
Tom.

Click to expand...

I also used a piece of angle on the edge to flex the skin. It was clekoed to the row of holes and a clamp ot two added. Then I used a big crescent wrench to bend the skin in one motion.

So I set up a test sample today out of some scrap 032 sheet that looked remarkably similar to some cut out of a horizontal stabilizer sheet (yes, that was a bad day). I created a template of the ear on F-770, mounted my angle then clamped it to the bench. I drew a bend line from the center of the polished notch (which I opened up to 3/16) to a position that was approximately 1" below the corner on the aft end of the bend (I do wish they specified the exact bend line in the plans). I offset the bench/angle clamp line by 1/32 to account for the skin thickness the way you would in a bending brake (it would help if this was also specified). I then performed the bend motion as best I could. I slightly over bent it, however it seemed to fit pretty well against the fuselage. I think the offset I used was pretty close to begin OK, I may have even been able to reduce this to zero offset as I had put approximately a 1/32 radius on the angle at the bend line per Larry's advice. Anyway, I think I now have to confidence to do one for real, and I really think the key is opening that hole up to 3/16" at the outset, then polish it well so you are not chasing cracks later on.
Tom.

I ran the actual bends and they came out fine. So the final procedure was opening the relief notches out to 3/16" with a file, sanding to a 1200 grit finish, then performing the bend with the angle clamped at zero offset from the bend line (but with a 3/32" radius on the bend line angle). I also cranked my heating in the shop to 18degC as final psychological protection against cracking. The bend center ended right where I wanted it. I think if I lived closer to the mothership and shipping wasn't so bad, I'd use a slightly smaller relief notch size, but I went with the 3/16" just as insurance.
I'm glad this step is over, but even more glad I didn't crack anything.
Tom.