Tank Bay Nut Plates

[DesertBearhawk]

Guys, I'm following the build manuals...in the tank install section you can clearly see in the pictures that the recess for the #6 screw has been machine countersunk (the tank bay frame not the cover) and NOT dimpled. How was this accomplished? I believe the material in that area is too thin to properly machine without having the pilot wander all over the place.

I'm at the point where I need to decide if I am going to dimple these holes or machine countersink. I would rather machine as it tends not to deform the edge like dimpling does.

Please Advise!

Thanks!

[mswain]

Dave, I dimpled mine without any issue.

[Craig C.]

Dave: Use a sacrificial piece of thicker stock for a backer. Drill and ream a pilot hole that is within .001" or so of the c'sink pilot. Use a spare c'sink as an alignment tool and then clamp the backer up to the bottom side. Now c'sink as usual. If you use a piece fairly think, .090" or more, it will last quite a while. Sand it down as necessary to fit confined and tight clearance areas. An alternate, if you have c'sinks with replaceable pilots, or ones with undersized pilots, is to drill the hole undersize, c'sink with smaller pilot, then ream to final size. We used to do this all the time with -3 and -4 rivets on small brackets and thin bulkhead webs and flanges on the F-16.