Countersinking nutplates along wing inbord edge

[Jskyking]

Today, I started preparing to countersink the #19 screw holes to fit a #8 flush head screw dimple. The K1000-08 nutplates on the backside are already riveted.
The issue is that with the nutplate attached the microstop countersink cannot get to depth because the pilot on the #8 countersink bit cant go deep enough into the hole/ nutplate to allow the proper countersink depth into the top wing skin.
I did a trial run on a test piece of scrap and even with max depth on the cage, the bit barely cut into the test piece.
Is there another type of #8 countersinking bit that has a smaller pilot to allow the cage to drop into the nutplate or is there some other technique to allow the countersink to reach the proper depth? ( see red circled areas denoted on RV14 plan pages 16-03/16-04)
Thanks
Jt

[WingsOnWheels]

Next time, countersink before you install the nutplates. For now you could removed the nutplate, or grind down the nose of the pilot.

[birddog486]

your countersinks have the same cutter angle just need to pick one with a smaller pilot that fits into the nutplate without damaging the threads

[Jskyking]

Thanks for the reply. After double checking my nutplates, I found that I had used K1000-8D nutplates vs K1000-8’s. ( they were in a separate box and I thought Vans might have just left of the D. I know now that the D, stands for dimple). Anyhow, I ended up going out this afternoon and removing the nutplates, though it might not have made a structural difference, Ill sleep better. Pretty painless job....Anyhow, even with the nutplates removed, the #8 CS pilot still didn’t work, so I inserted a CC6 bit ( a little smaller diameter pilot) and ran a couple of test passes. Worked like a charm. Thanks for the idea to downsize the c/sink. I’ll probably reinstall the nutplate before c/ sinking to reduce chatter or I may just use a backer plate behind the skin with a pilot hole sized to accept the cutter’s pilot.
Much obliged,
Jt

[MS1095]

A #30 countersink fits right into a #8 nutplate and keeps the countersink centered in the hole. The nutplate keeps the countersink from walking and chattering. I just did the tanks on my RV-4 this way.

[Jskyking]

Thanks, I’m going to run another test piece ‘this afternoon. It will be sweet if the #30 cutter works, because the #6 would have required a backer plate due to the pilot point not completely filling up the nutplate screw receiver.

[NorthernRV4]

As MS1095 posted, it's an accepted practice to use a c/s bit with a smaller pilot. The #30 bit does fit nicely into a -8 nut plate. I'll have to keep my eye out for when a -8D is called out compared to a normal -8. I had no idea there were both kinds.