The 7.2 degree sweep of the Skyote wing creates a challenge in making accurate matched pairs of spar mounted fittings. In the early stages of this project I designed a rather complex but effective ram style bender. You can see this bender in my post of Nov. 28,2007 entitled "Radius Bender". This bender is capable of producing bends which are very accurate in terms of position on the part and degree of bend and in a repeatable manner. It is, however" quite expensive and complex and somewhat cumbersome to use.
An upcoming "Group Buy Production Run" of water jet cut parts for other builders has inspired me to develop a more practical method of achieving accurate bending results.
This new method uses a common bending brake similar to those readily available from Harbor Freight or Grizzly, etc..
Anyone building a Skyote needs one of these anyway. This is a 36" brake. There are many options but smaller brakes don't generally have the backbone required to bend 4130.
I used the same 3D modeling software that was used to model the fittings to model a jig (fixture?) to accurately position the fitting in the brake. The jig assures both alignment and offset of the bend. A sheet metal "Counter" is used give the proper bend radius.
Only two simple parts are required. (1) A sheet metal angle made from 0.032 to 0.050 aluminum to serve as a radius shim over nose of the upper clamping bar to give the proper bend radius. (2) A precision alignment jig designed to position the part perfectly in the brake. That's it!
The jig is CAD designed, waterjet cut and the tabs are bent on my precession bender. This creates a pocket or back-stop which accurately positions the fitting. The up-turned tabs position the jig in the brake.
The "C" shaped jig provides offset and alignment. The angle provides the proper bend radius.
This is how the parts fit in the brake, clamped tight, ready to bend. Be sure the fitting is firmly seated into the jig. Of course, the gap between the upper clamping bar and the lower pivoting bending bar must be properly set.
After bending. This approach yields consistent results which is a requirement for matched pairs.
The operator is responsible for achieving the proper bend angle. A simple angle gauge for 97.2 degrees and 82.8 degrees will be provided with the fitting kits.
With a little practice you can get really close every time. Adjusting fittings which are a little over bent is easy. Also, you can C-clamp a stop onto the frame of the brake.
Only one jig is required for the 4130 kit parts because I made small adjustments (0.015"+/-) to all of the fitment models so the the bend offset from the edge of each fitting is identical. This method is considerably faster than my precision ram type press brake.
