Unfortunately the counter nut of my microstop machine countersinking tool just unlocked after 90 holes. Therefor the last 30 holes (top right spar) were countersunk deeper than the rest. I wrote Vans support an email to ask how to proceed. See the mail below: “I was recently working on the W-806 RV-8 main spars of the wings. As described on page 7-2, I installed the nutplates and the countersunk with the #30 pilot 100°-countersink the holes. I checked every 3rd or 4th hole to measure the diameter (I read in another post of the vansairforce.com to have a diameter of 0.370" (9.4mm). I also tried to fit a #8 dimpled 0.063" aluminum sheet. After 90 (of 120) holes to countersink...my microstop countersink had suddenly another countersink depth...deeper than before. since the last holes were just fine, I countersunk the last 30 holes without measuring. At the end the wing main spar RIGHT TOP SIDE is now countersunk deeper than all the other 90 holes (0.368" to 0.378"). The holes now measure between 0.385" (9.8mm) to 0.410" (10.4mm).” And this is the answer from Vans: “Christian, The ideal diameter for a #8 countersink is .370” so most of your countersinks should be fine. They are a bit oversized but not too bad. You may want to take a piece of .032 alum (fuel tank skin thickness), drill and dimple it for the screw and then install that scrap on one of the deepest countersinks. Tighten the screw and see if there is excessive distortion around screw head (cosmetic check… you may not like how it looks). Remove the screw and check the dimple for cracks around the hole perimeter ( if there’s too much space between the dimple and the countersink surface, tightening the screw can stretch the dimpled enough to crack the inside perimeter of the dimple…not desirable.
I’m guessing you’d probably be fine leaving the countersinks as-is but we do have a fix for them if you want to do that. See attached instruction sheet for repairing oversized countersinks. Steps are as follows. Remove the nutplate Use a step drill to
