Center Drill Question

[Paul Alciatore]

I have an old set of center drills that I got from my grandfather. Eight of them in a wood screw top case (well seven and one empty hole). The sizes are marked from A1 to F2 and the letters seem to indicate the larger diameters while the 1 or 2 following it seem to indicate two different sizes of the small diameter.

Looking in Machinery's Handbook, the sizes shown there are numbers only, 00 to 8 or so. Looking in the KBC catalog they show both styles of numbering but the ones with letters are much higher in price and marked subject to availability.

So my question is, are the letter designated sizes obsolete? Are they being phased out and replaced by the number only types? And is there a reason for this?

Paul A.

[wierdscience]

You sure the're not combined drill and countersinks?

[Paul Alciatore]

As near as I can see, the two terms, "center drill" and "combined drill and countersink" are used interchangably. At least for the 60 degree version. If they aren't the same, what is the difference. They sure look alike in the catalogs.

Paul A.

[C. Tate]

They are the same. I have always refered to them as center drills because they are used to center a part before turning or grindng between centers. Some may not consider them center drills because there was a time when a center drill was more like a spade drill that made a 60 deg hole with no relief in the front thus the name combined drill countersink.

CT