Drilled and countersunk rear window

I ground a #40 drill bit to a sharp point. I used this to drill the plastic without any cracking. I used light to moderate pressure on the drill and let the bit do the work. It took 6 to 8 seconds or so to drill each hole. For the holes on the roll bar, I chucked a regular #40 bit in another drill. I used the pointy one to drill through the plexi then switched to the other drill for the metal. I carefully started the bit; turning it by hand until I was certain it was on the metal and wasn’t going to grab the plexi. Worked like a charm.

I final drilled #36 the holes in the forward edge of the plexi and roll bar with a regular bit. Had no problems with the bit catching the plexi after drilling with the #40 initially. I tapped the both the plexi and the roll bar for #6-36 screws per the plans. I think the plans have you tap both the plexi and the roll bar together despite the fact that we’ll final drill the plexi to #27 in the next step to help ensure good hole registration. This should help to avoid any pressure on the plexi when it is screwed down that might cause cracks later. After drilling and tapping each hole, I lightly set a crew in the hole before moving on to the next.

I placed some tape along the forward edges where the protruded beyond flush with the window shim to mark it for trimming. I removed the window from the fuselage and Final drilled #27 with a plexi bit and countersunk all the holes in the plexi using a zero-flute countersink. This gave nice smooth countersinks. I used a vixen file to carefully trim the forward edge back about 1/32 in a couple of spots and smooth everything out. I used the edge of a pare of scissors to put a bevel back on the inner and outer edges where I had filed and then finished with 400 and 1000 grit sand paper.