On Tue, 28 Oct 2008 21:43:11 -0700, "Bill Noble"
wrote:

John - a couple of thoughts

first and most importantly - are you using a center drill for this?
otherwise the drill itself will wander.
second, drill opposites - e.g. drill hole 1, then drill the hole 180 deg
opposite hole 1 so only 1/2 error can accumulate
if possible, drill by bisecting angles
always center punch first - use dykem and a sharp scribe to layout


All Right! Thanks to suggestions from Bill and others, I've got a nice
index wheel, 15" in diameter, in 1/4" hardboard. The wheel will
rotate in a slot in a piece of 2x2 clamped to the lathe bed, with a
hole through the 2x2 for the pin.

I can't believe I was actually reaching around my brad point bits to
get the set of ordinary drill bits! Using the brad point bit allowed
be to get very good location by eye - I could just touch the surface
then raise the bit to check and reposition if necessary.

I tried using a center punch, then realized I was having to locate the
point in two dimensions by eye. Since the disk was going to rotate
under the drill on a fixed pin, I decided this wasn't necessary. If
I'd been drilling in metal that might have been required.

I'm laying out lines on wood for carving by hand - I don't need
thousandths of an inch accuracy.