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Countersinking nutplates along wing inbord edge

Jskyking

Well Known Member
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

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