Big day today. I started the day by transferring the marks from the spar attachment plate to the spar caps. This would provide additional confirmation on the hole locations, over and above the locations set by the flat plate drill guides. I prepped the welded drill guide by cutting it to the required clearance for the width of the spar. I also modified one of my practice studs to be used as an alignment pin for the backside of the drill guide. Using a hi-tech solution such (an elastic band) to hold the pin in the hole of the plate drill guides allows me to drill the hole perfectly perpendicular to the spar.
After doing some final fitment of the sockets from yesterday, I mixed up a batch of epoxy and thickener and set the sockets into final position.
After lunch, when the epoxy had set up enough to allow me to handle the spar, I attacked the critical and daunting though spar holes. These are the holes that pass from the front of the spar to the rear (or vice versa, depending on your perspective) and pass through the bolt holes in the spar attachment plate. Getting these lined up is critical. Not only to get the holes lined up for the stud to pass through the spar, but the location of the top holes in relation to the lower holes establishes the dihedral of the wing. Additionally, the three 8mm holes at the outboard end of each spar plate have some of the landing gear mounting bolts go through them. These also need to be lined up to one another properly or the landing gear mounts won't fit. Alignment, alignment, alignment. It's all so critical.
So after lots of measuring and layout and double checking everything, I clamped the drill hole guide plates in place and with the welded drill guide, started drilling. After all the prep, it was rather anti-climatic. I suppose that's what all the prep is for, to prevent anything from going wrong and keeping it dull. If it didn't work out it could have ruined the entire spar.
I drilled all ten of the 12mm holes and tested the studs for fitment with the spar plate in place. It all fits. Yay!
I've got to do the bottom ones yet but I'm waiting until I get my 8mm bushing for the 3 holes at the outboard end of the spar plate. Since the landing gear plates go through those 8 mm holes on both the top spar plate and the bottom spar plate, they are critical to the fitment. Hopefully that bushing material shows up in the next couple of days.