On 10 Apr, 18:35, Dave wrote:

Can't you drill the pilot holes from the top to ensure that they are the
correct distance apart and the right size and then make any mess under
the work top where it can never be seen after course correction?

Taps do not bend easily, but copper pipe does.

What we did, and this is the cunning bit, was to use *two people*.
One, holding the drill, judged his left-right perpendicularity (to to
speak), and the other (me) kept an eye on the fore and aft aspect.
Drilled pilot hole, then drilled with a spade bit from both sides (not
at once), two reasonably perfect holes, sufficiently oversize to the
taps that they could sit correctly.

What is this "copper" pipe of which you speak?

Regards
Richard