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  #1  
Old 12-11-2017, 12:27 PM
asw20c asw20c is offline
 
Join Date: Jun 2010
Location: Edgewood, NM
Posts: 147
Default Which Countersink Bit?

This past weekend I finally arrived at the step where the top skins over the inboard rib are countersunk to accept a dimple for a #8 screw. For those of you long past this step, or not there yet, the nutplates are installed earlier so this is the first time in the build where a countersink is required AFTER the nutplate is already there. No problem (I thought). I pulled out my countersink bit that specifically said it was for #8 screws, but I quickly discovered that the pilot (the little nub at the point) was too big to fit down into the nutplate threads and therefore I was unable to countersink as deep as is required. Does anyone know what size pilot will fit in these #8 screw nutplates (i.e. MS21051-L08 and K1000-08)? The bit that I was trying to use has a #21 pilot, so I already know that is too big. Will a #30 fit?
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  #2  
Old 12-11-2017, 03:07 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,616
Default

A #30 pilot on a countersink is a very close fit for a #8 nutplate.
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  #3  
Old 12-11-2017, 09:11 PM
Polar Polar is offline
 
Join Date: Oct 2013
Location: Central Alberta
Posts: 63
Default

I just completed that process last week, it's a bit of a haul countersinking all those holes. I did a couple with the nutplates installed but didn't like the finish of the countersunk hole. Eventually I clamped a 1/4" thick angle to the flange and match drilled all the #8 holes through the angle with a #23 drill, then countersunk them with a #8 countersink. It worked well, but scrapped some angle in the process. I followed the directions for the #6 screws, it worked well.




Quote:
Originally Posted by asw20c View Post
This past weekend I finally arrived at the step where the top skins over the inboard rib are countersunk to accept a dimple for a #8 screw. For those of you long past this step, or not there yet, the nutplates are installed earlier so this is the first time in the build where a countersink is required AFTER the nutplate is already there. No problem (I thought). I pulled out my countersink bit that specifically said it was for #8 screws, but I quickly discovered that the pilot (the little nub at the point) was too big to fit down into the nutplate threads and therefore I was unable to countersink as deep as is required. Does anyone know what size pilot will fit in these #8 screw nutplates (i.e. MS21051-L08 and K1000-08)? The bit that I was trying to use has a #21 pilot, so I already know that is too big. Will a #30 fit?
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