I made my flycutters/boring bars the same as Dave except I drilled and
reamed a 1/4 hole in the bottom end. Ream to a slip fit and use a dowel
slipped into the hole to measure over to the edge of the tool bit.
(Subtract half the dowel dia.)
Drill a 1/4 inche hole in the center of the work piece, install the
flycutter. Index the 1/4 dowel into the drilled hole and you stabilize
the tool to the workpiece. Hole will be dead nuts.
Remove the 1/4 inche dowel for flycutting, of course.
Oh, one more thing, you can slip a small spring over the 1/4 dowel to
hold the scrap down, if you wish.

Warren