Hi Folks,
My finish kit will be arriving within the next 2 weeks so I'm watching this thread with great interest.
Regarding drilling with a #40 bit, did you use a special #40 plexiglass bit or just a standard #40 bit that had been dulled?
Thanks
I used a special (pointy) #40 plexiglass bit. When we did the window, my friend who was running the drill was just a hair off center on one of the holes into the roll bar, resulting in a sideways force that broke out a chunk of plexiglass when the bit centered in the pilot hole in the roll bar. We had 100% perfect results with the replacement window by drilling each hole with the plexiglass bit in a Dremel tool, which made it lighter and easier to drill straight with minimal downward force. As soon as the bit was up to the pilot hole, we drilled the metal with a regular #40 bit in an air drill. That worked out great on the window and canopy. We did not have any damage at all from this part of the process.
As far as upsizing holes goes, the front edge of the window calls for you to upside to #36, then tap through the plexiglass into the roll bar, and then upsize just the window to #27 (which obliterates the threads you tapped when it was #36). The aft edge of the window has you remove the window and then final drill #27 the skins and window separately. The canopy just gets a #27 final drill after the initial #40 match drilling. We used pointy plexiglass bits size #36 and #27 for all of this and had almost no problems.
Of the 66 holes in the canopy and 55 holes in the window, we had chips occur in 4 of them. One was the center aft hole in the window, which chipped when we drilled it up to #27. That damage was easy to remove with a step drill since the skin will cover the oversized hole. The other three were on the part of the canopy that attaches to the rear frame, and occurred when we were final drilling #27 through the canopy and rear frame. One of those was so small that I had trouble finding it again yesterday. The other two were small enough that a dulled soldering iron tip just barely fit into the chipped area to "cauterize" the damage.
Read the other posts here and absorb their advice. Everyone here has more experience and skill than I ever will. The process I wrote out above is just one way to do it and the results that I experienced as a first-timer with help from an experienced A&P.
My only solid advice is this: When you are drilling plexiglass, whether match-drilling or final-drilling, be 10 times more patient than you thought possible and then slow down another 50%. It is much faster to drill 121 holes at 2 minutes each (4 hours of drilling) than to wait for a new window to show up, even if you have a money tree to pay for the new window.