Thu Apr 12 2007

Deburring and countersinking spars

When my dad and I did the countersinking for these nutplates, I had him debur the holes and demonstrated deburring on the rivet holes. He didn't realize he was supposed to debur the screw holes, too; and I didn't notice it until after the nutplates were attached. I've been considering taking the nutplates off so I could go back and debur the screw holes, but that'd be a lot of work. I tried my swivel deburring tool. It worked great.

Here's what they look like after deburring.

I started machine countersinking all the rivet holes on the spar flanges. While I was working, I noticed something...the match drilling only cleaned up the prepunched holes towards the interior surface of the flange. This is because the prepunching is essentially a shearing operation, and anytime you shear metal, it creates a "break" surface that isn't exactly perpendicular to the surface of the the holes are slightly conical. The match drill is large enough in diameter to clean up the small side of the prepunch, but not the large side. But if you look at the hole in this pic that is machine countersunk, you can see that the countersinking removes the material that wasn't cleaned up by the match drill operation. The result is a fully machined inside diameter. I was thinking those guys at Van's were really clever for selecting which side of the material to punch through. However, my appreciation was smashed when I looked at the other spar...the prepunching goes the other way, so after machine countersinking, there is a section of the hole that isn't cleaned up. Sigh.

You probably need to click on the full size pic to appreciate the detail of this dialog.

Got this spar fully countersunk!