I normally use a single-ended edge finder on the mill to locate work,
or more often the vise fixed jaw and work stop by zeroing on a 1-2-3
block. While it doesn't matter with a chuck, a single-ended one enters
a collet more easily. You might have to remove a tight collet to poke
a double-ended combo out if the spring-retained end jams.
A conical center finder may be thrown off if the top of the hole isn't
perfect, such as punched, worn, burred or manually countersunk. When
it matters I find or turn a snug-fitting pin and center on it with a
dial indicator, a Last Word or similar. That works for bearing holes
worn oval, by wedging the pin against the unworn side.
A wiggler may be somewhat less accurate but more convenient if you are
working to scribed or pencil lines or trying to duplicate an old worn
part. Unlike a center finder, regrinding the point after your spindle
accidentally drops it into the work doesn't affect its centering
This type of coaxial centering indicator is too tall for convenience
on my Clausing knee mill which has only 3" of quill travel.
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