Then I slowly used the sanding drum to enlarge the hole. This was an iterative process of moving the flap push rod up until it hit something, marking what it hit and sanding.
I disconnected the flap motor and pushed the rod up and down by hand. This was a mistake because I ended up making the slots too long for descending the flaps. The motor does not descend as much as I did manually.
I started in the fully up position to make the hole for the ball joint.
