I was countersinking the rivet holes for the three nutplates which are for attaching the inboard most Z bracket, but couldn't get the countersink cage over far enough to countersink the top and bottom most holes.

...so I carefully used my deburring bit to freehand the countersink. It worked perfectly for the left spar, but I went a little too deep on the right spar. Oh well, they're only holding nutplates on.