Brief Description: Countersink rivet nutplate holes in LH Spar
The plans call countersinking all of the nutplate rivet holes on the flanges and the web. These are supposed to be flush. I don't have a single flute C/S for my C/S cage, so I have to make due with the 3-flute ones that came in my kit from Cleaveland Tools. There's nothing wrong with the 3-flute ones, but I've heard it's easier to use the single flute to make high quality countersinks. Unfortunately, the only place I can find them to fit my C/S cage are sold by Cleaveland but they're out of the #30 pilot.
In order to get a good chatter free C/S surface I found you need to go high pressure and very, very slow speed. If the C/S starts to squeal then you're going too fast. The squeal is chatter.
The next step is to install the nutplates, but the instructions say to use a screw to align the nut hole with flange or web hole. Turns out the screws do not fit thru the main hole. There are no instructions to final size the hole, so I'm not sure how to proceed. I know the screw holes end up being knife edge (something that makes me shudder as a Boeing stress engineer), but I suspect when you countersink the screw holes you enlarge the hole and the screw will fit.
Unrelated to this step, I discovered that I cut my short J-stiffeners from the wrong stock length and I need to order two more 6 ft. pieces. Vans has been aware of this since at least 2013, but hasn't added a simple note to say "Use 8 ft. stock to fabricate all the J-stiffeners in this section". This pisses me off to no end. I used two 8 ft. and two 6 ft. leaving me short for the stiffeners in the LE and fuel tank.
I marked the screw holes with a Sharpie so I wouldn't accidently C/S them
These are the type of shavings (long and curly) you want to see for a chatter free C/S surface
There are 14 nutplate rivet holes on the web. These nutplates are on the outboard end of the spar
