In article , Nick Müller
writes
wrote:

Centre drill are often used as spotting drills in the lathe
but there's a pretty wild mismatch between center drill point
angles and the the usual jobber drill that follows. Special
spotting drills are produced for NC use at about three times the
price of similar centre drills.

How do the special features work and are they worth the
premium price? Some seem to be single flute designs and the
included angle is usually less thqn 118 deg jobber drill angle.

I use them a lot on the mill, seldomn on the lathe. I like them!
The keep long, because you won't drill deep holes, and you can't and
should not drill holes. Just the conical part.
Mine are two-fluted.
Buy them!

I have never used a spotting drill - and don't know what their
construction is. However, just an alternative idea for pentagrid: have
you tried stub drills. I almost always use these for starting holes,
especially in small sizes. They are about half the length of a normal
jobbers drill bit, and hence much stiffer, but only cost about the same
or a little more. I do often spot with the very tip of a centre drill,
but I'm not sure it is necessary.

David
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David Littlewood