Deburred the #30 holes in SS firewalls using step dril bit (Uni-bit) in slow electric hand drill which works very well on SS. Will also use step bit to enlarge the FW holes for AN3 and AN4 engine mount bolts where needed. I will not try to match updrill the SS when clecoed to the fuselage since using a step bit typically would not be long enough to penetrate the SS and fuselage angles and trying to updrill SS with a regular bit is asking for trouble, IMHO.
Spent about 2 hours engine turning the firewalls. Used a "OneX" vinyl stencil on the bottom FW and "1X" on the top. I have also used vinyl shelf liner which works well too if you don't have access to a vinyl cutting machine. Used a dremmel tool with a 1 1/4" cutoff wheel and hot glued to the cutoff wheel was a circular piece of a Scotc bright pad I cut out with scissors. Actually used two Scotchbright disks for both FWs. Pretty simple process and adds some bling to the engine compartment.
