After having read most of the (French)articles about RAB in this forum, Jacques Davin and myself made the following RAB. This is how we proceded :
1) Take off the srcrew on the inside of the boot, which holds the shin-part to the shoe-part. On the outside of the boot there's no screw, but a popnail, which I took off by drilling it, starting with a 3mm metal gimlet and finishing by a 10mm gimlet, watch out not touching the plastic of the boot.
2) I exchanged the popnail by a custom-made screw, picture 02 :
Take a cylinder with an outside diameter of 10mm and inside screw-thread for 6mm screw, saw it about 10mm, then saw a screw real short and screw it with a big ring and stick it with loctite; put it from the inside of the boot through the hole in the shin_ and shoe-part. Another screw with a big flat head will be screwed from the outside into the cylinder.
3) With a cutter I cut off backparts of the inner and outpart-lips of the shoe, picture 03; this will help to more and easy flex of the boot.
4) I grate the inside of the tongue, also for more and easy flex, pic.04
5) The spring-system is made from:
* Upper part: 4mm stainless steel plate welded on the upperside to a tube(inside diameter: 5mm) on the other side bent to about 95°; the original pin of the boot goes through the tube to fix it and a whole is bored through the lower part of the plate and the backside of the shoe-part; a 4mm screw keeps the lower part of the plate stuck to the shoe.
* Lower part: small 4mm stainless steel plate welded ass well to a tube (inside diameter: 5mm) kept in place by the original pin.
* a whole is drilled in each plate to pass a 5mm stainless steel bar, 115mm longue. This bar keeps the springs and to prevent scraping I put a plastic tube around the steel tube.
* At www.rabourdin.fr
I bought 10 different kind of springs (17.41euros):
2 times 32mm upper springs will guide the flexion of the boot:
green soft: 32mm longue and outside diameter 16mm ( ref.355-16-32)
blue ( ref. 356-16-32)
red tough ( ref.357-16-32)
One 25mm lower spring will guide the extention of the boot:
red (ref. 357-16-25)
All together it cost me about 30 euros.
I tested this RAB just a few days ago in the French Pyrenees and I'm very satisfied about the result.
I weigh 80 kg and put a green and red spring for flexion-guidance and a blue spring for extension.