A little more progress made today; check back shortly for slides.

The first operation I did today was to make sure that the tips of the horizontal stab's full ribs, which eminate from the rear spar and flush up against the forward spar at its ends, and the small nose rib were coplanar. The instructions have us do this by placing the assembly leading-edge down and check the three points against the flat surface of the table; I did this, and all three ribs seemed to meet the table just perfectly.

It's not the easiest thing to judge, since there are two factors that come into play to keep the structure from being very rigid at this point. First, the full ribs are clamped but not rigidly attached to the end brackets which are at the ends of the forward spar. In fact, the very point of checking to see that the tips of the ribs are coplanar is so that if they are not, a small adjustment can be made at the full rib/end bracket junction to bring them into a coplanar condition. Second, no skin on the structure means that there nothing to keep the forward and rear spars from moving relative to each other, pushing the other compoents through angles other than 90 degrees.

So, what I did was lay the assembly upside down--to take advantage of the flat flange on the top edges of the spars and ribs--and then adjust the full-rib-to-forward-spar-end-bracket junction so that the end brackets were perfectly centered on the full rib where they meet it there at the ends of the forward spar. Then I clamped this securely in place, and gently stood the assembly up on its leading edge to judge the degree to which the three ribs were coplanar.

They seemed to be, so this told me that no particular adjustment between the full rib and the forward spar end brackets would be necessary, and that they should simply have rivet holes located and drilled so that the end bracket would be centered on the full rib.

So I removed the end bracket, drew a line on the flange of the bracket where it meets the full spar's web area, used the rivet fan to space three locations for rivet holes on the line, and drilled all three holes #40 bit.

Then I attached the end bracket back onto the forward spar using holes already drilled, clecoed it, and then I clecoed the center hole of the three on the flange that meets the web of the full rib--that is, the center hole of the three I just drilled on the end bracket. It seemed to me that with one flange of the end bracket fully clecoed to the forward spar and the center hole of the other flange of the bracket clecoed to the full rib, that I could safely and accurately drill the other two holes on that side--above and below the center hole--through the full rib's web using the existing holes in the end bracket as guides, and that's just what I did.

I repeated this process on both sides of the forward spar and then checked the entire structure for squareness. I also rechecked the three rib tips for coplanarness. All seemed to be well--I noted that the coplanarness of the rib tips was less perishable, as it were, than the squareness of the structure's components. That is to say that coplanarness of the rib tips could be maintained (within my ability to detect) despite a small relative movement between the forward spar and the rear spar, but that, of course, any relative movement between the forward and rear spars destroyed the squareness of the structure. The good news is that it was easy to get both squareness of structure and coplanarness of the tips at the same time--and I'm sure that's the important thing. Once the skin is on, there'll be no relative movement between the spars anymore, and that will be that.

This being completed, I transitioned to opening up the holes on the forward and rear spar to #30 in anticipation of corrosion protecting and riveting. PTI brand zinc chromate and reducer is on hand to do this when the time comes, but I need to get a few foam brushes to brush it on with.

Opening the holes was very easy to do--I simply silver clecoed every third or fourth hole in the spar-to-doubler structure, opened up the holes between the clecoes, then copper clecoed every third or fourth of the newly drilled holes, removed the silver clecoes, and drilled the remaining holes. It's easy, but it does require care to ensure that the center of the #30 drill bit starts out in the center of the #40 drill bit hole.

My method for opening up the holes that were located to hold the ribs in place (on both the forward and rear spar) was simply to silver cleco the top and bottom holes of the four that hold each of the ribs in place, drill #30 bit between the clecos, copper cleco the newly drilled holes, remove the silver clecos, and then drill where the silver clecos had been to finish the row of four holes. I did this process seven times: once each for the two full ribs, twice each for the rear ribs, and once for the single nose rib.

I did not touch the front mount holes yet because these holes require opening to a #20 bit, and I am unsure about whether it is a good idea to go straight from #40 to #20. I think I'll use the #30 as a transition so that the center of the holes stays relatively stable as the size is increased. This may not be strictly necessary, but I'd rather do it and have it not be needed than, in the interest of time, not do it and wish I had later.

I had a bit of time left, so I used lacquer thinner to clean up all the parts, removing the sticky labels and the various Sharpie marks I had made. I found that the lacquer thinner removed even the various foundry labels and marks that are sprayed on the metal as it is produced; after cleaning, there's absolutely no marks of any kind on any of the parts. Luckily, they'll all go together only one way.

I cleaned up and put up, and that was that for tonight. Time spent tonight was about an hour and a half.

Check back for slides and for additional updates.