A fairly big build day today. I opened up my center section package that came with the wing kit a couple of years ago and laid all the pieces out on the table.
First item of business is to drill all of the pieces for the snap bushings. I had set up the drill press and the unibit to enlarge the holes that are pre-drilled for you. I started with the F-704C and D pieces, then moved on to the F-704A and B outermost holes.
Next I began to mark out and drill the innermost holes on the F-704B (aft) bulkhead.
The more tricky part is marking out the holes on the F-704A (fwd) bulkhead. Vans provides you with dimensions, however these make the holes extremely close to the rivet holes for the center ribs. Many folks have noted this issue in their build logs. To make things worse, the holes in my fwd bulkhead are not symmetrical making the left side ok, but the right side is certain to have edge distance issues. I must have measured and re-drawn the hole locations about 4 times. Very frustrating and slow work. Nobody really comments on the logs and forums as to the acceptable solution. I found that the RV9 vertical dimension was 1 19/32, as opposed to the RV& being 1 17/32. I also reasoned that the 5/8" hole for the bushing was just a wiring hole, so I decided the best approach was to preserve the edge distance at the expense of slightly moving the location of the 5/8" holes. The right side hole will need to be moved slightly above and to the right to maintain proper clearances.
Drilling was a tedious process, many measurements taken and adjustments made during the drilling to ensure the holes were perfect. I do not want to mess up this part! In the end, I'm extremely pleased with the outcome. Edge distance from both holes to the center of the rivet was 0.2655" which is well within limits.
Next step was to attach the 704C & D pieces to the 704 A & B center sections and fit the close tolerance bolts. I will admit that I did not enjoy this process. Very stressful to get those bolts in, with the fear I might be doing something wrong. I used a small amount of aviation grease and then wiped it off so the bolts weren't dry. I noticed that left side went much better than the right side on the aft bulkhead. It only took firm pressure with the palm of my hand, while the right side took a couple of light taps with my small mallet. After examination of all the bolts and trying them all. I found this. Not all bolts are the same. Some bolts fit a tiny bit better than others, often the bolts hang up on the initial insertion as they tend to have a very slight bulge after the threads stop. I've read comments that this happens to the bolt when they cut the threads. In this area, some of the cadmium plating comes off when inserting the bolts. I most certainly will buy new bolts during final assembly, but these ones will be sacrificed for the build process. I should note that the bolt fitment improves once you have the bolts in and out a couple of times. (But its still tight, which is good).
Next I set up the assembly on the drill press to match drill all the holes.
I then installed the 704-G vertical bars with AN4 bolts and clamped the assembly. Using the hand drill, I "Marked" the holes with an initial drill. This gives a really good pilot hole to use on the drill press with reducing the chance I oblong the hole or drill it crooked. As I have found...never miss an opportunity to use the drill press when working with thick material.
Finishing up the #30 holes on the drill press.
