February 18th, 2008
Countersink Spar for Nutplates
I spent 2 hours tonight drilling and countersinking the spars for the wing tank attach nutplates. There are a lot of holes to countersink and my arm was plenty tired by the time I finished.
Update: 2-24-2008 READ FIRST
Learn from others mistakes! I ran into a problem using the #21 countersink. The issue has been described many times in the forums by other builders but I did not take the time to research it before I started on the spars. Check out the links below. The bottom line is the
depth of the center c'sink for the screw is such that there is no material left on the back side to support the pilot of the countersink . You need something back there to guide the pilot. So don't use the #21. Instead use either the Van's method of riveting the nutplates in place and using them as a guid or make your own guide. I chose to make my own guid because I wanted to be able to debur the holes before riveting the nutplates on. See my next log entry.
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Original Post
The first thing I did was tape of the spar so the metal shavings would not fall down between the spar and the stiffener. They can be a real pain to clean out. I used the blue painting tape. It is easy to peel off. Pay attention to the plans and only drill the holes that are for the fuel tank nutplates. You can also countersink the nutplate holes for the three inspection plates on the bottom of the spar. I did this because I already had the countersink set up. i also went ahead and drilled the other spar while I had everything set up. One thing to note is the size of the countersinks.
Here I have just completed the first pass of countersinking. It was really easy. I just took my time and made sure each hole was just right.
So I follow Brad's site quite a bit. If you haven't visited his site take a look. He has lots of good information. He made a tool that I thought was really cool. You take two rivets and sandwich them between two pieces of aluminum to make a jig for countersinking the #8 screws.
You can then clip the jig along the spar for using the #30 countersink. This will help you keep the countersink centered.
Once I did all that I was like Duh! I bought the Isham kit and he includes a #21 drill bit and countersink for #8 screws! Yeah. This thing made the whole thing a piece of cake. I ended up not using the jig I made but it was fun to make. Oh well.
Here's a glory shot of the finished holes after using the #21 countersink and drill. One thing to note is you have to be very careful not to over drill the hole. The bit will chatter and make a lousy countersnink. I plan on trying the vans method tomorrow of riveting the nutplates on and using a #30 countersink. I will post what I find out. I finished the left spar and will tackle the other one tomorrow.
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