DJ Delorie wrote:


The offset you care about is the center of the bit relative to the
center of the bushing. The offset from the finger to the bit is
irrelevent here - the jig is designed to accomodate *that* offset.

When pondering your diagrams, think to yourself "the bit is to the
left of where it should be".


OK, I got this -- I figured out what I was missing. Although my sketch is
correct as far as the comparison in offsets between pins and tails, that's
only 1/2 the story, when the router comes around to the other side of the
pin or tail, the other side of the bushing contacts the jig, thus, just as
you said the pin or tail is offset to the left or right by the amount of
the difference you stated, from center of bushing to center of bit (the
other difference to the bushing edges cancels out). As you stated, if I
rotate the router 180 degrees, I'm shifting the fit such that the pin and
tail board will be offset.

Thinking about this, all other things being equal, rotating the router 180
degrees should be a way of measuring how far offset the router bit is from
being centered in the bushing. It should magnify the offset by 2 if I'm
looking at this correctly. That might be useful for measuring that offset
in a straightforward way -- cut the pins and tails with the router rotated
180 degrees and measure the test piece misalignment. Doesn't help any as
far as being able to make the adjustment to fix it any easier since one is
essentially rotating a base anchored by 4 fasteners.

Thanks for setting me straight -- what can I say, an EE doing ME stuff.

--
If you're going to be dumb, you better be tough