Drilling firewall components5h
August 18, 2022
Today I continued working on the firewall bulkhead.
The first step was to drill the stiffener I fabricated from the angle stock to the firewall.
Then I continued with fitting the angles to the firewall bulkhead. The angles need to be spaced at 3/32" from the bottom stiffener, so I used a drill bit to space them. I used cleco clamps to push them against the vertical stiffener.
Then I drilled the holes in the angles using the firewall as a template.
Fabricated a small part, the brake plate. I drilled two pilot holes that will be used later for drilling the holes for the brake line fittings. I figured it would be easier to drill the holes to #41 first, then upsize them to the fitting size with the unibit drill bit.
Then I moved to the firewall recess. When I was test-fitting it, I found that I can force to the existing holes except for the two top #30 holes that just don't fit. To avoid damaging existing holes on the firewall and the stiffeners (which are critical for the structural integrity) I decided to upsize holes to the #40 size on the firewall recess separately from the other parts (knowing that recess holes match well the firewall). It worked fine, the recess holes match the firewall holes very well (except for these two holes).
I don't know what to do about these two mismatching holes, but I am not in rush to figure it out -- the recess is installed later in the process after the rudder brace is installed. One option is to drill the hole with the parts (which would result in a very oblong hole) and hope that rivet would sit well enough. Another option I can think of is to put the rivet under the flange in these two holes, assuming that there are enough rivets to keep the recess in place.
After that, I drilled all the holes to the final size.
The next step would be to counter-sink the stiffeners and dimple the firewall. Also, one hole on one of the angles turned out to be just a bit oblong (it measures .140") -- I need to decide what to do about it. The firewall and stiffener holes are okay, so maybe I will just redo the angle. Or install a rivet expecting it to swell and fill the hole. The hole is oblong only on one side (I think, I tilted the drill while reaming).