Deburring Rib holes and Marking Pitot Tube Mounting Holes

Well I was finally able to stop researching and get out in the shop to do a little metal work for a change. A rough few weeks at work, weather, and a head cold have kept me pinned down a bit, but tonight I was able to do a few small things.

First, I was able to debur almost all the holes I had previously match drilled in the main ribs where they slide underneath the main wing spar flange. I deburred both inside and outside holes f the wing spar as well as the ribs. Now I just need to finish drilling and deburring all the wire run holes and hopefully I can move on the prepping them for primer.

Then I decided to perform the steps to mark the hole locations for the pitot tube mast. Neither the pitot tube nor the mast holes are drilled at all, so you must locate, mark, drill, debur, and tap the holes.

1. mark the center of ech screw mounting point of ghe pitot tube. This is identified by the 4 thicker areas of aluminum that protrude deeper into the top face of the pitot tube as shown below:

2. Carry the line down the side of the pitot tube and continue the line past the point where the pitot tube base widens out.

3. Measure the height of the recess in the pitot tube to the top of it. Mine measured about 22/32. I then took half of that value, or 11/32, and marked the pitot and mast accordingly. This will effectively put all the mounting screw at the halfway point of the mounting flange of the pitot tube.

4. Slide the pitot mast over the pitot tube. I also used electrical tape to fill the slight gap between the outer edges of the pitot tube and the mast - this is typical of the pitot and mast that I am using. Some use electrical tape and others use heat tape. All you are trying to do right now is get the pitot tube to snug up against the wall of the mast so you can drill accurate holes through both of them.

5. Transfer the vertical lines onto the mast, and then measure the 11/32 from the end of the mast on both sides and draw the intersecting line on each side of the mast.

I center punched the hole locations on the mast and decided to stop there for the night. My plan is to gradually upsize the hole to make sure that it maintains the correct angle based on the mount points built into the pitot tube. The last thing I did was to reposition the drill stop on my #40 drill bit to just over a 1/4 inch. The mounting screws can not really be any longer than that,or you risk drilling into the actual air lines or heating element inside the pitot tube. You can order either countersunk or pan head screws from ACS, or I was able to find some 3/8 inch long, 6/32 pan head stainless steel screws at  local hardware store that I plan to use for my setup. Lots of folks go ahead and get countersunk screws for this, but I just did not want to go through the trouble. Neither of the screw types sits absolutely flush to the round pitot mast, so I am ok with just using the pan heads for now.

And lastly a shot of the electrical tape wrapped around the mounting flange of the pitot tube:

The tricky part of all this is drilling the holes at the correct angle and depth. I plan to use my drill press for this so I can clamp the work at the correct angle and ensure that the drill bit will maintain a straight path into the tube. Will try to do all that tomorrow.