15 MAR 09 - Spar Countersinking and Nutplate Installation (Part II) - 6.0 Hours
We ran to Home Depot and bought a digital
caliper to ensure that our countersinks were the right dimension for the #8 and
#6 screws. According to
a post on Van's Airforce,
the proper dimension for the #8 countersink is .365" to .375" and #6 is < .325".
I used .370" and .320", respectively, as my target dimensions.
I followed the directions and used the installed nutplates as the guide for the
#30 countersink bit for the #8 wing tank attach screws. There has been a lot of
discussion as to alternative methods to produce a more accurate countersink, but
I found the nutplate method worked perfectly and all of the countersinks turned
out very nice.
I did use a cordless drill with a low speed, high-torque setting instead of using
the air drill. The process took a long time, but I'm happy with the way the countersinks
turned out.
After the #8 countersinks were complete, we riveted on the #6 nutplates for the
inspection covers on the bottom of the wing, and then countersunk the holes for
the #6 screws, using the same method as before with the exception of using a #40
countersink. Again, no problems were encountered while using this method.
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