Kit of six Plexiglass drill bits from Avery Tools.
Van’s plans call for using a #27 drill bit and although the kit has one, will be using the slightly larger 5/32" Plexiglass bit. This will allow for a slight bit of wiggle room and also provides room for the window to expand and contract without placing excess stress on the holes. In fact, Van’s support staff has suggested doing this to other builders. So a thin piece of plywood was placed under the window, then the window was clamped onto the plywood and the holes on either side of the clamp were drilled using the 5/32" Plexiglass bit. The idea here was to keep downward pressure on the window while it was being drilled so the back edge of the hole was being supported as best as possible.
The difference between the 5/32" Plexiglass bit on the top and a regular 5/32" drill bit on the bottom can easily be seen in this photo.
Drilling the screw holes in the RV-12’s aft window using a 5/32" Plexiglass bit.
The aft window had some rough edges on it so used a sanding block to smooth up the edges. Did not totally finish the window because I need some finer grit sandpaper. Plan on going up to 1000 grit so the edges of the window will take on a polished look and this will also mitigate the possibility to stress cracks as well.
Rough edges on the aft window can be seen here.
Smoothing the edge of the aft window with a sanding block.
At some point in the future, the plan is to very lightly countersink the edges of all the holes in the aft window using a countersink cage and finish off polishing the edges.