Built form blocks and plugs for flanging the lightening holes. I used 3/4" (18mm) MDF for this. Having read many accounts of the flange forms cracking, I was worried they wouldn;t last long. I used the router to create the 45 degree angle on the plugs, then put a second piece on top to double the thickness. I managed to flange all the holes without cracking any of the plugs. I think I got lucky!
I built a bob stick to flatten the ribs after flanging,
