What I have been doing is holding the drill bit in front of the screw at
eye level and trying to sight it to see if I can still see the shaft of
the screw behind it. If I can just /barely/ see it, then I know that the
screw's shaft will be a smidgeon larger than the hole it's teething into,
and that's what I'm aiming for usually.

Yeah, I do that too, plus a little trial and error.

2. Should a pre-bore be large enough to only grab the threads? Or is this
only necessary for the harder of the hard woods?

I think the answer is that it depends on the wood, and to some degree on
the position of the screw.

IME, I seldom need to predrill at all in softwoods. If I am close to the end
of the board, where splitting is more likely, I will predrill more often and
more agressively.

However, I have found reclaimed very old (soft) wood to be brittle and
absotutely required predrilling.

IME, the harder the wood, and the larger the screw, the more particular you
should be about pilot hole size.

Cheers,

Steve


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