On Thu, 13 Dec 2007 21:39:43 -0800 (PST), woodworker88
wrote:

I've recently noticed a problem with drilling in steel that I want to
ask the group's opinion on. The problem is the drill grabbing in the
hole, and it only happens in one situation (unfortunately, a common
one). The problem happens when I try to drill out an existing hole
which is larger than the web of the larger drill, which you should
avoid when choosing pilot drills, but in which I often don't get a
choice (if it's modifying an existing part). Since the web of the
drill does not regulate drill feed, the drill tends to "bite off more
than it can chew", take a large chip, and bind. This happens most
often when drilling in the lathe, and tends to spin the drill chuck
rather violently in the tailstock taper. I know this isn't just a
general taper issue, since it works fine when drilling a full-diameter
hole in the same material, same setup, etc. The drill bits are brand
new, very sharp American drill bits in the 3/8"-1/2" size. Feeds and
speeds, etc are not the issue, nor is the material any more unusual
than mild steel. The primary machine is a 12x36 Atlas lathe, but this
has happened in other machines in the past as well.

My main question is about chipbreakers. When dealing with cutters
that tend to "bite off more than they can chew", such as parting
tools, I have had good success grinding appropriate chipbreakers into
the top edges. Since I can visually confirm that the binding is due
to the taking of an inappropriately large chip by the drill cutting
edges, it would seem that this is an ideal solution. However, where
would I go about grinding a chipbreaker into the cutting edge of a
drill? I do have a set of drill bits with small vee grooves factory
ground perpendicular to the middle of each cutting lip, but I don't
recall if they were advertised as chipbreakers or some other purpose.
I can't actually try using them since the proper sized drill from that
set has long since been reground normally in the course of normal
sharpening.

My question is whether or not grinding such a groove into a normal
drillbit would solve the problem and, if not, if there are any other
suggestions that people have to solve the problem?

Thanks in advance,
woodworker88


This is a pretty common problem, even when drilling soft metals like
aluminum. Simply grind a very small flat along the cutting edge of the
drill so that the sharp edge formed by the flute and the end of the
drill is made a narrow flat parallel with a center line drawn through
the length of the drill.









Bruce-in-Bangkok
(Note:remove underscores
from address for reply)