Counter sunk the Pitot Tube Mast and Checked out the LE from the Inside

Since I received the AN507 6R4 screws from ACS, I decided it was time to do the deed and countersink the mounting holes in the mast to accept the new screws. I had an opportunity to practice this a bit before going to town on the real thing by using the half inch of mast material that I cut off as described in my earlier posts. Some of my pics turned out really blurry so I won't show the close ups.

To countersink the mast mounting holes I did NOT use a microstop countersink tool, as this is next to impossible to use since you are countersinking a hole on a curved surface. Other builder sites have reported that it is almost impossible to get a totally good countersink on these mounting holes because of the curved surface of the mast.

So I did everything by hand by using 2 different deburring tools. I started by using my single flute deburring bit in my electric drill. I made sure that the deburring bit was angled in the same direction that the original hole was drilled, and that the bit was as square to the hole as I could get it. Once the countersink was started and I could not go any deeper with this tool, I switched to my larger 3 flute deburring tool that has a larger countersink bit on it.I removed a little material at a time, maybe only 3 light turns each time, as I got closer to the final depth for each screw. The last thing I wanted to do is make the countersink too large for the screw head. After countersinking each hole I would remount the new pitot tube into the mast and tighten down each screw to check the depth, and then carve out some more metal if necessary and do it all over again.

Practicing on the scrap piece of the mast helped, because that allowed me to get a feel for what it would take to get the right depth for each screw. Here are some pics of the tools used and the new screws  think I have some more work to do on one of the forward holes, but the rest of them seem pretty good to me.

Next is the work on the LE. I removed all clecos attaching the LE skin to the Wing Spar flange, and then I removed all clecos attaching the rear LE rib flanges to the wing spar web. Note to self, remember to apply all these clecos from the rear (bottom) of the wing spar web, and NOT through the top or front of the web. When I attached the LE to the modified W408 rib it was already attached to the wing spar and I had mounted the clecos on the top or front side of the wing spar web. The goal for this removal was to remove the entire LE assembly from the wing spar, leaving ALL ribs and the subskin clecoed in place so I could inspect the new holes and clearance on the edge of the rib flange.

To do that I was faced with trying to figure out a way to remove 3 clecoes attaching the 408 rib from the wing spar web. I really had no other choice other than to remove the clecoes holding the LE skin to the 408 ribs again, but that would mean starting all over again, so I got creative and figured how to get my hand inside the lightening holes of both 408 ribs with the cleco pliers in hand, and then working the pliers with one hand by reversing the pliers to face the clecos, and feeling my way around in the blind until I new I had attached the pliers to each cleco. The clecoes are hidden from view so all of this has to be done by feel. I managed to get each one undone, but I really do not want to do that again. SO next time all LE attach clecoes will be inserted into the ribs from the rear (bottom) of the wing spar web.

With the fully assembled LE finally off the wing, I was able to check my handy work. Here are the pics of the top and bottom rib flanges where I had to trim away some of the rib flange to allow clearance for the shop head of the rivet that will go into the closest hole (where the cleco end is currently. At a galce it looks like the shop head of the rivet will clear the flange, but I need to make sure it will clear AND not rub against it, so I think I have just a bit more filing to do, but its real close:

This next pic is a bit bright due to my flash from the camera, but it does show some detail of the inside of the LE area that I have been working on:

You are looking at a close up of the bottom rib to LE skin flange with the LE laying on its side. You can see the area where I trimmed the rib flange for the clearance for the original rivet hole that will go through the outer skin and the sub skin only. (Last cleco on the right). The next cleco to the left is the new rivet hole that I drilled that will attach the outside LE skin, subskin, and rib flange (3 layers of metal). I can also see that I have at least the required 2xD edge distance, or in this case 1/4 of an inch from all sides of the flange (rear, outside edge, and inside bend radius).

The rib flange is sitting on top of the extended subskin, and the outer LE skin is sitting under the subskin.So with a little more filing I think I will have sufficient clearance for the shop head of that right-most rivet hole that normally would have gone through the final hole in the W709 rib, but since I am not using that rib any longer this is the change that I had to make.

After I get this clearance issue done I can start prepping the ribs and outside skin for primer, and then I have to rivet the rear rib flange additions to the web of the modified 408 rib (The six holes at the top of the above pic, plus the ones for the other side of the rib). Then I get to make even more critical measurements on the subskin so I can start trimming that up to its final form. Hopefully the pics  provide a bit more clarity to my explanations about what I doing here. Getting there......

KPR.