Fuselage: Firewall. Forward assembly, tunnel and center completed.

The firewall comes together.

I didn't bother to look at how well the F-01401G-R and F-01401D firewall angles laid up.  The left side fit fine (left).  But the right side did not (right). 

I observed this after the sealant cured and after 3 rivets holding the F-01401D angle were set (left).  So I had to drill them out to get the parts to lay up properly.  The angle could easily pop up under minimal flex, so when I added the F-01401J angle and F-01401R gusset, the clecos kept it down.

The sealant  needs to cure before final riveting commences.  So here it had to sit for a week or so.

Sometimes I needed to cut away the sealant bead at the joints of the parts, otherwise I couldn't get the mushroom set to have a flush surface to buck against (the second-from-left rivet manufactured head looks bad but it's actually okay).  This bead was a consequence of using too much sealant at the joint between the F-01401A firewall top and F-01401B firewall sides (see below).  To mitigate this issue in subsequent steps, when sealing in the F-01401C firewall center, I smoothed down the bead immediately following sealant application (see upper left image)

I found it impossible to buck the rivets at the gusset.  Well, that's not true.  I couldn't buck any single rivet since they were so closely spaced.  I could have back riveted, but the rivets were slightly oversized, leading to a significant clenching-over risk.  Determined to find a way to squeeze as many as I could, for the outboard rivets, I used my longeron yoke.  For the inboard ones, I used the 3" yoke with a 1/4" tall squeezer set.  This, combined with folding in the flange on the firewall top, allowed me to reach in deeper (see below).  The inboard-most two rivets had to be bucked, which was completed with the help of a friend.  I could have used my  4" deep yoke, but I was concerned the rivets would clench under the yoke's flexing.

Curious when these two boys get riveted, from page 27-07 (left)?  It happens on page 29-14 (right).

Bucking the rivets at the nose gear brackets is tough.  Because the part is steel, it absorbs a lot of the impact energy from the rivet gun, robbing the bucking bar (Mr. T!) of its efficacy.  I had to use 100 psi on my 2x gun.  The bottom rivets were instead squeezed with the longeron yoke.

After much generous bucking help from a gracious friend, here's the firewall, completed.

A few places need spot-priming on the aft side due to the sanding out of minor bucking bar scuffs.

This is a rivet map showing which rivets I was able to squeeze (green) and which had to be bucked (red), either classically or via back-riveting.   I found that some upper row AN426AD4-6 rivets on the upper angle F-01401J were too long and clenched over too easily.  Using my rivet cutters to create a batch of -5.5 length also caused clenching due to the way the rivet shaft is sheared.  So I sourced a legitimate batch AN426AD4-5.5 rivets (actually MS20426AD4-5.5) yielding great results.

One of my blog readers indicated to me that he back riveted his entire firewall by placing the assembly face down on an undersized table (otherwise the flanges would lift the assembly off the table).  I think that's a great idea, especially if you're going solo.  I tried it for a few rivets but my shop just wasn't equipped to adequately realize that approach.  I share his approach hoping that someone will find it useful.