Brief Description: Firewall - Process stiffeners and gussets.
So, after you drill the stiffeners and gussets you think your almost done. Not a chance. You take it all apart, and - 1.) Counter sink stiffeners and gussets. 2.) Debur stiffeners and firewall. 3.) Polish stiffeners and gussets. 4.) Etch (wash with special acid soap). 5.) Prime stiffeners and gussets. 6.) Dinple fiewall. and then you can finally rivet.
So, here all i'm doing is counter sinking the stiffeners and gussets. These parts have both #30 and #40 holes. In each case I went a bit deeper with the counter sink bit to allow the dimple on the firewall to fit better.
Not all the gussets and spacers get counter sunk. In image 3, the bottom 6 pieces plus the one piece with the 2 square holes get counter sunk. The rest leave alone.