The pile of parts that were prepared over the weekend were cleaned, scuffed up with a Scotch-Brite pad, wiped down with Acetone and primed Monday … it was a productive day and all hanging locations in the shop had painted pieces hanging from them.
To make the most of more upcoming good spray
painting weather, decided to continue preparing parts for primer and top
coating as necessary. Next up was the F-1203A Bulkhead which required quite a
bit of attention. There are three side by side holes at the center bottom of
the bulkhead that require being enlarged to 7/16” and two adjacent holes that
required being enlarged to 3/4". Step drills are a great choice in this
situation, so the drill press was outfitted accordingly and the drilling
Using the drill press outfitted with a step
drill to enlarge one of the holes in the F-1203A bulkhead to 3/4".
The plans call for lots of machine countersinking
on the forward side of the F-1203A bulkhead … a total of 46 rivet holes for
AN426AD3 rivets to secure nutplates and 6 #30 holes along the top edge for 120
degree flush pop rivets. In the photo
bellow, the areas that require work are outlined in red … the 46 #40 rivet
holes are circled in red and the 6 #30 holes requiring 120 degree machine
countersinking are marked in green.
Holes in the F-1203A bulkhead requiring machine
countersinking marked & ready to meet the machine countersink cage.
Machine countersinking one of the fifty two holes in the
F-1203A bulkhead per the plans.
The F-1203A bulkhead is made from .040 aluminum …
this is near the upper suggested limit for dimpling. Thicker materials are usually
machine countersunk but the decision has been made to dimple the bottom of the
bulkhead for the flush rivets that are being used on the RV-12 project. The
bottom flange of the bulkhead is not quite 90 degrees so knowing thicker
material tends to flatten out a little when dimpled, an angle gage was used to
measure the angle before dimpling so that angle can be reset after dimpling.
Dimpling the bottom flange of the F-1203A
bulkhead for the 120 degree flush rivets being used on the RV-12 project.
The dimpling process relaxed the bend of the
flange only a few degrees so it was tapped back into place with a soft hammer. Next
the flange angle was checked to verify it is now at the same angle as it was
prior to dimpling.
Checking the angle of the F-1203A bulkhead flange
after dimpling and subsequent adjustment to verify the angle is the same as
prior to dimpling.
Even though the autopilot will not be installed
until much later, the RV-12 forum consensus is to install the autopilot mounting
brackets now while building the fuselage as opposed to installing the brackets
afterwards. The autopilot bag was opened and the brackets were removed, deburred
and prepped for primer.
Almost done smoothing the edges of one of the autopilot
servo mounting brackets … four down one to go.