How to make 'Tight Fit' Bolt Holes (Sept 10th, 2003)

The fore/aft fuselage joints (the fuse longerons of a Sonex are not going thru all along the sides, but instead they're split behind the pilot's seat and joined by strips of aluminum and eight AN-3 bolts (4.8mm diameter) at each of the four corners. These AN-3s caused me some grief during the last months. When I used a 0,1875" stepdrill, then it became an 'easy fit' - not good. So I decided to enlarge the holes and use oversized HI-LOK fasteners (see 'August 2003' page). These are 5.11mm in diameter and there's absolutely NO drill bit of this size available. At special stores in Germany one can buy drill bits in increments of 0.1mm (0.004"). The 5.1mm drill however is too small, the 5.2mm too loose (for my taste). So the way out of this dilemma was to grind down a 5.2mm bit by 0.09mm. This is the way I did it:

Placed a 280 grinding stone parallel to drill bit, lubricated well and ran the drill at 3000 rpm. It taks not much effort to remove this tiny bit of steel.

After fifth test hole I got it right. Bolt slips in with a good pressure of thumb. Grinded down drill bit is shown at right side.