Well, I've got to say that I was expecting this to be easier. This entry represents about 12 hours over 3 days It's become my routine to peek at several build logs on line before jumping into a new section, in order to get more of an overview than I can sometimes see in the build instructions. Mostly when it came to the vertical stab people just said stuff like "uncle bob came over and helped with the vertical stab. don't cut too much off the front" In my case, it was a little more involved. I spent way to long figuring out what was going on here and where the potential trouble spots are, so I'm going to attempt to document it in detail here in case it might help out anyone else down the line. Clamping the vertical stab in place, you have 4 dimensions to account for; 1- height of the rear spar at the F-712 bulkhead 2- perpendicular to the H/S 3- rudder hinge line straight. 4- leading edge offset 1/4" for left turning tendencies So, lets jump in; The plans have you cut 5/8" off the fwd spar so it will nest nicely with the H/S at the fwd attach interface, but several people on VAF hav had issues and said that was too much, so I started by cutting off about 1/4" just to see what it looked like. To cut to the chase, here are my observations; If you locate the aft spar properly, 5/8" is probably in the ball park, but I can see how jut a little error back there could really effect the front. Also, you move the front attach point up or down to adjust the hinge line on the aft spar, and between those two things, I can see how you could run out of spar stub real quick if you cut too much off and were required to move it in that direction. Anyway, trial fit seemed okay, but the upper rudder hinge was about 1/8" too far aft. i.e. with the aft spar clamped in position, the front spar needs to be brought down in order to bring the upper hinge fwd and get all 3 in a common plane so the rudder will swing without binding. It can't come down any further because I only trimmed off 1/4" so, back to the bench and trim off another 1/4" I repeated this process until I had taken off approximately 5/8" or maybe even a little more. I should also mention that the way Vans tells you to check this is with a straight edge at the aft edge of the hinge brackets on the v/s. The implication is that if the hinges line up, the holes in the hinges will line up. Before betting the farm on that, I checked with a mic and sure enough, the holes vary in location by as much as .030 fore/aft. I didn't build the v/s, it came with the used wings I bought, so I don't know if they came from vans that way or if there was some variation in the way the previous guys cleaned the holes up. At any rate, a straight edge along the back of the brackets isn't going to give me a good result, so I did what many others before me have done and ran a tight string through the holes so I could check alignment. Anyway, to circle back to what I said before, the top hinge was too far aft. In the build instructions, it says to adjust this the fwd spar stub can be positioned either side of the F-781 attach plate and that you can also shim as necessary. it says to position the spar aft and maybe add a shim to bring the top hinge aft. For the longest time, I couldn't see how pushing the fwd spar aft at the bottom could bring the upper hinge fwd. it seems counter intuitive. I played with this for a long time trying to figure out what was happening here, and finally it became so obvious I felt stupid for not seeing it immediately; because the fwd spar and attach plate are canted at an angle to everything else, if the spar is aft of the attach plate, it's also lower. Ergo, you can raise or lower the fwd spar slightly just by which side of the plate you put it on. That's really what this adjustment is about; raising or lowering the fwd spar stub, which brings the aft top corner of the v/s fwd or aft. The instructions also give you a dimension and material callout on drawing 27A for the shim, but no thickness callout, which indicates that it can be any thickness it needs to be, within reason, to get the job done. Looking at it this way, the limiting factors on the length of the fwd spar stub then become a max of when it starts to interfere with supporting structure (too long), or when you run out of edge distance on the pre punched rivet holes on the F-781 attach plate (too short), depending on how you have to adjust it vertically to bring the hinges into alignment. If you get need to move the top rudder hinge WAY fwd, it's also possible that you can run into trouble with the attach plate lapping up on top of the flange of the lower v/s ribs which stick down and are riveted to the fwd spar on both the fwd and aft sides. Lot's of stuff potentially going on here. I didn't realize all this when I located the aft spar vertically per print, and while I got it as precise as I could, looking at it after the fact, it's ever so slightly lower than "perfect." You can see this in the picture below that shows the bolts installed through the hinge bracket if you know where to look. The sharpie marks should be aligned with the upper surface of the upper hinge bracket in that picture. It's lower but about he width of a sharpie line. This, combined with the variation in the hinge brackets, caused me to have to make many adjustments, trimming off a little bit of the fwd spar at a time until I got it where I wanted it. more on tis a couple of paragraphs down. I didn't mark 5/8" from the end before I started trimming, so I don't know exactly how much I trimmed off, but I have a sneaking suspicion it was probably 1/6" or so more than the 5/8" callout. I think this because when everything was positioned correctly, the upper edge of the attach plate was lapped up on the flange sticking down from the nose rib at the spar by about that much. Fortunately, I needed a .032 shim between the spar and the attach plate, which is also the thickness of that flange, so it can overlap slightly and everything still sits flush with solid edge distance on all the rivet holes both top and bottom on the attach plate. I feel like I dodged a bullet there, and I could have eliminated a bunch of this monkey motion by just scooching the aft spar upward by about 1/16" which would have made everything in the front a corresponding bit longer and likely eliminating the need for any shimming. Once I had all this figured out, I clamped it with about a billion clamps, remeasured everything, and reamed the aft v/s spar to the evaluator up stop and put some bolts in there to hold everything in position. I then remeasured everything again, was feeling pretty good about myself, and then realized it all had to come apart again. Now the real fun begins; on a taildragger, there are three bolts that go through the bottom of the aft spar, through the bulkheads, and through the aft flange of the tailwheel weldment, which of course, you can't see except with a mirror. Lots of opportunity to blow edge distance on one components or another. Took a bunch of measurements to identify location, then removed the v/s and pilot drilled #40 through the bulkhead into the weldment. The lower hole is centered on the tooling hole on the F-712 bulkhead, so that one was easy, but the upper 2 can blow out the e.d. on the tailwheel weldment on the fwd side or on the lower rudder hinge on the aft side if you're not careful. Once pilot drilled, I measured everything inside with a small scale and inspection mirror to confirm good e.d. on the fwd side, then re-installed the v/s, this time with the washer on the left side between the spar and the up-stop per print to allow for the 1/4" offset at he leading edge, and match drilled #40 from the inside with a 90* drill. This allowed me to confirm good e.d. on everything on the aft side. Now that everything was pilot drilled, it was a simple matter to bring the holes up to full size. Note- You have to pay attention here, because on print 27A (tricycle gear) there are 4 AN3 bolts here that go into the tail tie down structure. On print 27 (tailwheel, the 3 bolts are obviously a different location and configuration, but they are also a different size (AN4). Since I'm building a 7, they are AN4 bolts, so I upsized these holes by drilling them slightly under and then reaming them final size with a .249 reamer. Once the aft side was done, I snugged down bolts in all the holes, verified the offset up front and once again measured everything, especially the rudder hinge line to make sure nothing had shifted. Then I upsized the bolt holes common to the F-781 attach plate and the HS-710 & HS-714 angles by drilling them up from #30 to slightly undersize and finishing them off with a 3/16" reamer. Snugged some bolts down in them, then FINALLY match drilled the fwd spar stub to the F-781 with my 90* drill and enough holes that I could get some clecoes in it and make sure everything is going to stay put. Once again removed the v/s unclecoed the F-781 and shim and primed them. Looking back on what I just wrote, I can see a bunch of wasted effort here, Now that I have an idea what the end result should be and what gotcha's need to be accounted for, I could have done a bunch of these steps in a slightly different order and saved myself about 1/2 of the put-together-take-apart-put-together operations. But, they payoff for all this is that tomorrow I'll rivet F-781 to the fwd spar stub and this thing should just drop together smooth like butter.