Tuesday, May 26, 2015

Creating F-12117 Lower Cowling Hinges

The F-12117 lower cowl hinges are made from 10" of hinge material and need to be placed on top of a 10" spacer which moves the hinge material slightly away from the fuselage … which I’m guessing creates a gap necessary for the fiberglass cowling.  The two 10" F-1201W spacers are cut from a strip of flat aluminum that is already the proper width.

Moving onto the hinges …. hummm, now where is that hinge material? Gee there are just not that many places in the hangar to hide quite long pieces of hinge material. After searching the wooden crate, shelving and looking everywhere in the hangar, seemingly forever … finally revisited the wooden crate I thought the hinge material should be in and finally found it. It had slipped under some cardboard that protects the rear window material. Apparently vibrations from moving the crate to the airport caused the hinge material to go into seclusion.

Because the 10" hinge length is longer than the throat on the band saw, cutting the hinge material required making two cuts. Wanting to use the band saw for the cut, the hinge material was placed at an angle and the hinge was cut slightly longer on a bias and then trimmed to the proper length.
Using the band saw to cut the hinge at bias so the piece of hinge material can clear the throat of the band saw.
A pair of  F-12117 lower cowl hinges and one of the 10" F-1201W spacers.

The DOG Aviation fuselage skins and lower firewall flanges are already dimpled for flush rivets, so the plan is to clamp the hinge and spacer onto the firewall flanges and then carefully match drill the hinge and spacer. After the pieces are drilled, the hinge and spacer will be Clecoed together and the rivet holes machine countersunk from the spacer into the hinge.  The countersinking will go all the way through the spacer material and should only remove a very small amount of material from the back of the hinge material. Overall I feel countersinking the spacer is a better solution for this hinge as opposed to dimpling the hinge material. For a true test, took the time to rig up scraps of hinge and spacer material and did a test machine countersinking of the pieces to verify the hinge material did not get cut into too deeply … no problems.
F-1201W spacer material and right F-12117 lower cowl hinge positioned and clamped onto the lower firewall flanges ready for match drilling.

Didn’t get to match drilling the hinges so that will be the first item addressed during the next work session.