"DoN. Nichols" wrote in message
...
On 2010-11-10, Michael Koblic wrote:
The purpose of center drilling is to start the hole exactly where
intended
without the drill point wandering all over the place, yes?

Actually -- that is the purpose of spot drilling -- with a spot
drill, not a center drill.

The purpose of a center drill is to make a conical depression
with a precise 60 degree angle and a bit of clearance to allow room for
the point of a live or dead center to stablize the end of a workpiece in
a lathe.

Yes, people do use center drills for the purpose of spotting
drills -- but that is not what they were made for.


Very informative as usual Don.

*****
Wiki
Center drills, numbers 1 to 6Center drill bits are used in metalworking to
provide a starting hole for a larger-sized drill bit or to make a conical
indentation in the end of a workpiece in which to mount a lathe center. In
either use, the name seems appropriate, as the drill is either establishing
the center of a hole or making a conical hole for a lathe center. However,
the true purpose of a center drill is the latter task, while the former task
is best done with a spotting drill (as explained in detail below).
Nevertheless, because of the frequent lumping together of both the
terminology and the tool use, suppliers may call center drills
combined-drill-and-countersinks in order to make it unambiguously clear what
product is being ordered. They are numbered from 00 to 10 (smallest to
largest).[9]
*****

Hmmm... Would it not lend itself then to the thought that even on a lathe
you should first spot drill and then center drill?