I've seen machinists use a small block with a bunch of holes
in it where the tap would be inserted to guarantee that the
tap threads straight into the hole to be threaded. I could simply
drill a clearance hold in some scrap metal, but if I wanted to
machine such a guide,there must be some good ideas out there.
It could be a rectangular solid with a row of holes different
diameters, it could be a disk, etc. What do most people use?

I know of other techniques using the drill press chuck, a spring-
loaded tap guide, etc, but in this application, I would like a simple
guide.

Jim