Marking Backup Instrument Holes

Yesterday was the first work session at the DOG Aviation hangar in quite a while. Between family obligations and getting sick a few days after Christmas, quite a few unseasonably warm work days were missed and now we have cold and snow to look forward to. The temps are forecasted to take a deep plunge and although still not feeling 100% yet, decided it would be in my best interest to bring home the chemicals that should not be subjected to freezing weather. The chemicals such as fuel tank sealant, primer, epoxy resin, RTV, thread sealants, etc., were being stored in the heat box which has done a great job thus far …. However, the forecast is for a huge drop to 6 degrees so felt it best to remove chemicals from the hangar altogether.

While at the hangar, decided to at least try to get something small done … so decided to mark the locations for the mounting screws for the backup instruments.  I used the UMA airspeed indicator as the template for marking all the holes. The instrument was placed in each panel hole and aligned. Of note: For those builders desiring to install backup instruments, be aware that the side edges of the panel pieces ARE NOT square and should not be used as a reference point to align the positioning of the instruments. To keep the instruments square, measurements need to be taken using either the bottom edge of the panel piece or any horizontal line cut by Van’s … such as the cutouts for the radio or glove box. Or better yet, use the method I thought of while typing this post ... see below.

Using a metal straight edge against the instrument and a plastic square against the glove box slot the instrument was rotated until the gap between the two was even. However, this is doing it the hard way … see note below.

Once the instrument was in position, a #14 drill bit was placed in each mounting holes on the instrument and spun a few times to mark the center of each hole. The reason a #14 drill bit was chosen is that it fit nicely inside the holes with little slop and could be easily turned with the fingers without much binding.

It is hard to see but I'm using a #14 drill bit to mark the center of the mounting hole for drilling. The black drill bit being used does not show up well in the photo against the black instrument case.

This method of marking the center point for the mounting screw holes worked great and left nicely defined marks that were center punched to ready the two panel pieces for drilling. During the next work session the screw holes will be drilled with a tiny drill bit and then brought up to size so #6 black brass mounting screws can be utilized. Decided since a vertical card compass will be attempted in the panel, it would be best to use all brass mounting hardware for the backup instruments.

Note: While writing this post, it occurred to me that I could have saved myself quite a bit of time aligning the instrument in each hole had I thought to use the digital level. Squaring up the instrument with the digital level would have been a piece of cake and only taken a few seconds. A good example of performing even the simplest of tasks while sick, may not yield good decision making.