I'm embarrassed to admit how nervous I was about drilling the first two holes in this process, but the you google this task, you get a multitude of build sites about people who've had problems with blowing edge distance here. The problem is that once you get the horizontal stab located and triangulated to ensure it's where it's supposed to be, you have to lay out a hole location that works for the HS-714 angle on the fwd spar, but also works for the F-718 Longeron and the F-710B spacer. These 3 angles are stacked up with the aft deck covering the lower two and they're oriented at approx 85* to each other. Doing the arithmetic, there's 8 separate opportunities that I can think of to blow edge distance on a structural component with that one hole, and you have to put one on each side of the airplane. Of the three, the F-710B is the least critical, and when people have run into trouble here, Van's has previously approved some pretty skimpy edge distance on this component. In fact, I saw a couple of build logs online where people had received quickbuild kits with with this part woefully shy on e.d. On the other hand, they are not nearly as forgiving if you blow the e.d. on the longeron. The fix for that has quite often been to add doublers, which I want to avoid if at all possible. I'd really like to get his right the first time. Way back when you first start building the fuselage, you fabricate the F-710B from angle stock and rivet it to the bulkhead, then way later in the process the F-718 main longerons stack on top of it; Make it too long and it won't nest in the radius of the longerons properly- too short and you blow the already meager available edge distance. If you see that this might be a problem, too bad so sad. You can't pull the hole inbd without blowing e.d on the main longeron, doom on you. With that in mind, about a year ago when I was working on this part I had made the length as precise as I was capable of, and radiused the end so it would hopefully nest snugly in the corner of the longeron when the time came. I spent quite a bit of time on it to give myself the best chance of success. As I mentioned, out of all the components involved, the F-718 longerons are the most critical. The build instructions are very specific that you should strive to put this hole dead center in the middle of the space available on the horizontal leg, which works out to be 5/16" from the edge and 7/16" from the apex of the angle. The implication is that if you have to fudge it somewhere, this is not the place to look. Step one was to verify that the fwd edge of the HS-714 angle matched the fwd edge of the F-710B, which at this point is hidden under the aft deck. I tried a couple of things to measure this and ultimately decided that the simplest way was to stick a plastic protractor under there with the flat edge butted up to the F-710B, then draw a line on the protractor around the edge of the lightening hole, then pull the protractor out of the hole, line up the circle I just drew, and then draw a line on the aft deck along the straight edge, thus transferring the edge of the F-714 to the top side where I could see it. Once that was done, I transferred the edge of the longerons to the aft deck by simple measurements, and verified that the rivet line down the edge of the aft deck was basically the line that I wanted. I then positioned the horizontal stabilizer side to side, clamped it to the vertical bars at the aft spar and discovered that sure enough, the fwd edge of the hidden F-714 was about 1/16" fwd of the visible edge of the HS-714. Both of those angles are 1", so there's plenty of meat there to work with as long as you know about it first. I measured back 3/8" from the fwd edge of the HS-714, which will give me 2d edge distance longitudinally on that part and about 2.5 e.d on the F-710B. Potential longitudinal catastrophe accounted for. NOTE- Both HS-714 and F-710B are 1" angles, and it could be tempting to push this dimension up greater than 3/8" to center the hole on the available 7/8" of the horizontal flanges on these angles, but if you push the hole aft of 3/8" youre going to run into edge distance problems on the aft corner of HS-714 where there is a radius at the termination of the horizontal flange. Do yourself a favor and measure in every direction possible and really think about it before you commit yourself. I then transferred an intersecting line from my longeron rivet line to find the sweet spot. So far so good. At this point it looks like this will work, as long as it doesn't get too far out of whack when I do the final positioning of the H/S. I had drawn a longitudinal centerline on the aft deck and had lined up the center butt joints of the H/S spars on it, but now I got out the tape measure and verified that it is correctly positioned laterally. It was off by about 1/16" or so, and I nudged it back and forth until I got it where I wanted it, measuring from multiple points a bunch of times during the adjustment. Once it was right, I started triangulating the tips with various points fwd on the fuselage. After I had it right, I left and had a cup of coffee. Came back and measured again. Had another cup of coffee. Measured again. Tips were maybe off by about 1/16" Adjusted, found a different point to measure from. Decided that it was no good to measure to the h/s tip because one skin might be filed back slightly more than the other at the leading edge to account for the gap in the elevator horns. Remeasured from the firewall to the outermost rivet at he fwd H/S spar. Measurement was just shy of 161-9/16" on the right side, 161-11/16 on the left side. Is it really out or is the tape just sagging? Took a break and went to Costco with RJ and picked up a Freddys burger for lunch. You get the idea- basically, I had worked myself up into a freak out state about this stupid thing and just needed to walk away for a while. Came back and got the measurement consistently between dead nuts on or within 1/32" depending on where I measured from, clamped it down tight and called it good. Went back and verified my sweet spot was in the same ballpark. When trying to lay out a hole this precisely, even a thin point sharpie line is pretty fat, so I used a my favorite thin steel scale to exactly reference the dimples in the top of my reference rivet line, and popped a starter hole with a center punch. Once I was sure it was absolutely perfect, I pilot drilled with a 6" #30 bit, then stuck a #30 bit in the hole because it would hold it more perfectly that a cleco, and drilled the other side. After all that sweating and scheming, they came out just about perfect. The result was exactly 5/16" e.d on the longerons (per builder instructions) good e.d. fore & aft, and 4/32" e.d. to the end of the F-710B on each side, which is honestly, about as good as is physically possible, given how this all stacks together. Holy cow, I'm glad that's over. I feel like I just defused a bomb. Tomorrow I'll fabricate the shims that go between the HS-714 and the aft deck, upsize these holes to final size and drive forward.