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Now the other one.  It’s pretty much the same routine.  Mark up the flap skin and drill the pilot holes.  Then line up and drill the ribs.  In the second picture you can see that this process has just been started. The silver clecos are the ones used for match drilling the pilot hole. Then all of the holes are updrilled to the rivet size.  

At the start of the project I had several dozen of each #40 and #30 drill bits.  The #40’s for the pilot holes and the #30’s for the finished rivet holes.