"David Littlewood"
wrote in message
news
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
--
David Littlewood

I tend to use sheet metal drills for hole
starting. They are very short and are double
ended. you can break twice as many for the same
price!