On the first set of HS spars I used a coupon method to check the depth of the countersink.  If you are unaware of how this is done I will not educate you with the wrong method.  Suffice to say that section 5 of the manual says to take a microstop countersink and set it to a depth 7 clicks (each click is a thousandth) deeper than the proper depth to countersink the factory head of the rivet.  IE 7 thousandths deeper than a setting that would yield a width of 0.176 (see mil spec detail sheet on Vans website).  This does not give you the measurements for the new width.  After a little geometry using the sine and a triangle drawing I was able to figure out the proper width per .007 deeper with a 100 degree deburr bit should yield a proper width of .193 wide for the countersink into the spars.  The proper method to countersink thin material like this is as follows:

1. Set scrap material below thin material to be countersunk. 
2. Match drill hole.
3. Countersink to proper width of .193″.
4. Repeat another 615 times for the RV-10.

The scrap material is so the pilot of the countersink has something to guide it.  When you countersink into thin material the pilot will begin to wallow out the thin material.  This time I got it right and used the aluminum angle I had around for the rudder TE build to match drill and countersink on top of.

The replacement spars are now deburred.