I haven't posted anything for a couple of weeks, but that doesn't mean I haven't done anything. I'm at the point where I need to countersink a bunch of holes in the VS-808PP rear spar doubler. I figured I'd better practice on some test pieces before I commit to doing something irreversable on the actual part.
I drilled a bunch of #30 and #40 holes in a 0.063 in. scrap aluminum sheet and started practicing with the microstop C/S cutters. It seems no matter what I did either fast or slow, light or heavy pressure and all combinations in between I had a massive amount of chatter. This sucker was screeching like a banshee! I used generous amounts of Boelube, but it didn't seem to help. My C/S bits are the 3-flute type from Cleaveland. I read about single flute C/S bits, so I ordered a couple of #30 and #40 bits. Hopefully that will solve my chatter problem.
The plans call out for AN426AD4 rivets with dimples in the rear spar and C/S in the doubler. I made a dimpled coupon to figure out the correct size of the C/S. After a lot of trial and error, help from the Vans Air Force web site and a through re-reading of Section 5.5 in the plans I finally got a good fit.
Section 5.5 says C/S until you get a flush fit with a rivet, then go 0.007 in. deeper.That's 7 clicks on my microstop. I tried it and it was a perfect fit!
Waiting for my new bits to arrive before I proceed further. In the meantime, I'm going to build my spray booth.
Test dimple coupon and my first countersinked holes. C/S is way too deep. Coupon wiggles around.
Hole on the right is C/S for rivet. On the left is for a dimple. Difference is 0.007 in. depth.
