A marking spacer is used to trace the 5/8" flange around the firewall
formblock:
Here is what it looks like before cutting:
The recessed area at the bottom has a 1/2" flange. The remainder has a 5/8" flange.
The firewall was then cut out using some shears. A backing board was
made from some extra MDF that I had laying around the shop. It was
made about 1/4" smaller than the firewall formblock. The stainless
steel was properly positioned between the formblock and backing board and
the whole sandwich was clamped using several "C" clamps as shown
here:
The dead blow mallet was then used to form the flange much like was done when forming the wing ribs.
When the firewall was formed as much as possible, it was removed from the
formblocks. The edge looked something like this at this
point:
The corners are especially ragged. I was able to borrow a shrinker
from a friend of mine. His entire shop went under water during hurricane
Katrina and this shrinker was submerged under salt water for several hours.
It was quite rusty. I brought it home and submerged it in a pale
of moor oil for a couple of weeks then took it out and cleaned it up. Its
still a bit rusty but works like a champ:
The shrinker has two sets of jaws that grab the edge of the metal and then
pushes it together slightly. Its easy to over-do it. Done correctly,
the results are pretty good as can be seen in the below photo of the
firewall:
The edge has been shrunk is nice and smooth but the corners needed a bit
of extra fluting to get them to the correct angle and curve. The idea
is to get this part as flat as possible so its easier to get an air-tight
seal between the flange and the side walls. I'll use some high temp
sealant i the flutes on final assembly.
Here is the completed firewall after it was back-drilled and bolted to the
fuselage:
The little splotches are actually my fingerprints all over the place.
And finally, here is the firewall with the engine and mount bolted in
place:
As a double check, I clamped the nose bowl in place and ran the strings as before. Everything fit perfectly and the strings make a nice smooth transition from nose bowl to instrument panel and door flanges.
Firewall
Completed: 03/04/06
Total time: 16 hours