Yesterday afternoon I attacked the task of putting a big hole in the instrument panel to accept the avionics stack. I've discovered that the easiest way to make big holes is to use a large bit in a drill press to make a series of holes close to the intended line. Then it is a fairly easy task to use a nibbler and a large file to finish the job.

Today I slipped the Garmin GNS-430 GPS/Nav/Com and GTX-327 Transponder into the trays and stacked them on top of each other on the bench. I carefully lined them up so the face of both were lined up with each other, and then marked a reference line on each side of the trays. The reference line gives me a fighting chance of ending up with the face of the two boxes even with each other. It also gives me a reference to measure to when attempting to mount the racks so the back edge of the protruding part of the avionics box is almost touching the instrument panel.

Next I clamped the two racks together, clamped the angle that goes on the right side in place, and marked the location of the holes for the screws that attach the racks to the angle. There are little "feet" on the racks that keep them a little bit apart, so I found that I needed to slide a piece of 0.040" sheet in between the two racks when I clamped them to avoid deforming them.

The angle that goes on the left side of the racks is already attached to the back side of the left sub-panel in the aircraft. So my next trick will be to figure out a way to hold the racks in position against that left side angle so I can mark the location of those holes. Then I'll drill the right angle to the instrument panel. I'll be narrowing the face of the angle that goes against the instrument panel from 0.75" to 0.50".