Boy, has this one been answered. There was a long time
contributor to usenet who is no longer with us who explained it
all better than anyone has or will. I am proud to post this as
some of TeeNut's finest work:
Jim, You are dead right about not being able to grind a drill
help! Well here's how you create your own "6 Million Dollar
Bionic Darex" ;^)
Let's assume we are going to sharpen a 3/8" diameter, 2MT shank
about 8" long (these figures are arbitrary..I just want every one
to have the
same mental picture of what I am describing.) We approach the
wheel, which has
been dressed on its face, dead straight across with no
grooves..(Ve SHOOT anyone
ve catch putting grooves in ze drill wheel!!..No Pity..No
The drill shank is held firmly in the RIGHT hand...ALL the
movement and control
is imparted by the RIGHT hand. For the purposes of drill grinding,
the left hand
could be...with benefit..a LUMP OF CLAY!!
It is from this "lump of clay" that we fashion the Bionic Darex".
Place your left hand thumb and finger tips LIGHTLY together..Relax
three fingers aand let them naturally curl against the palm of
your hand. Let
the drill flute drop into the vee between thumb and fore finger
and let the tip
of the finger "Find" the curve of the flute where it fits
comfortably. The tip
of the thumb rests on the sharp junction ot the land and the
flute, about an
inch back from the drill tip.
Now...SQUEEZE HARD!!! YOUCH!...I said it would be easier if it
were clay! 8^)
Lift the drill from your fingers...see the GROOVE?...Drop the
drill back in..it
locates within a thou or two! Magic?..Bionic at least! Squeeze
again to set the
groove. You have created a customised drill guide that fits
better that that on
any machine ever built! You can relax your grip now..feel how
drill will ride back and forth, guided by the groove you have
created for it.
Place the knuckles of your left hand, LIGHTLY on the ginding wheel
and swing the drill shank, from left to right (using ONLY your
right hand) and
push the drill lengthways though that groove in your fingers back
or forth using
the groove to make the drill twist or "rifle" in your fingers. Do
NOT move your
left hand in any way..it is made of clay remember!
A) The drill axis is "eyeballed" to be at half the required point
angle to the
wheel face...You can scribe or chalk reference lines on your
grinder benchtop to
help you line this up..at least untill it become almost second
B) The drill axis is dropped JUUUst below horizontal. This will
your soon to be ground drill lip will start with a "smidgin" of
(Ideally, and certainly for a beginner, the grinder rest should
be set dead
radially to the wheel center and about half the drill diameter
below the true
center of the wheel)
C) The two cutting edges of the drill..the straight, sharp bits,
formed by the
junction of the flute and the back face (the only bit you grind),
horizontally disposed..with the edge uppermost on the side closest
to your left
hand..the othe sharp bit of course, pointing downwards (Jeeze
this would be a
lot easier with a sketch pad)
This I will call the SET or START position!
NOW, move your left hand for the first, last, and ONLY time during
th is whole
exercise. GENTLY ease the cutting edge towards the spinning
maintaining all the angles and orientations of the SET
cutting edge is JUST shy of touching the wheel. If you listen
will hear the tone of the entrained air, whistling through the
You will hear a subtle but distinct change of tone JUST, I mean
tenths of a thou BEFORE the edge touches the wheel. STOP!!!
FREEZE!! DO NOT
Now, press the knuckles of your lump of clay..sorry, your left
hand FIRMLY down
onto, into and around the grinding rest..establish a "Groove" on
the back of
your hand as well as between your fingers.
We are now ready to grind, Your left hand locked to the drill and
is otherwise quite relaxed..letting the drill slide, twist and
your right hand and the groove in your fingers tell it to go.
The actual grinding is a bit of an anticlimax.
You have previously studied a new drill point, you have read about
and cutting angles, and rakes and......
With the RIGHT hand in control, gently, kinda, lean forward...
squeezing your arms hands and body..rather than actually moving
take up that last couple of tenths and the wheel begins to cut.
cut..don't force it, and dont' rush it..it really won't hurt
anything if you
take a full minute Per pass per face. YOU and your "Bionic Darex"
in control of that drill and the wheel..Forget the times when,
close to panic,
you swung the drill wildly past the wheel, hoping to get "the
dirty deed" over
with as quickly as possible.
Take your time, enjoy the moment, THINK about the shape you are
generate. Just the one face is left to "Interpretation"...every
aspect,angle, facet, what have you...Has ALREADY BEEN TAKEN CARE
OF!! and is
locked in place under your control!
The right hand should perform a "Lower Quadrant sweep" for want
of a better
term..An observer behind you would see your hand move from about
17 minutes past
the hour on a clock face, to roughly 25 minutes past. But it
isn't a smooth arc
of a circle, more a sector of an elipse..You see, as your hand
starts to drop
slowly, you are also rotating the drill in "the groove"..the first
third of the
turn needs to maintain that very slight clearance angle on the
cutting edge, and
not increase it too rapidly.
You need the clearance to cut..But too much at that point will
WEAKEN the edge,
and cause the drill to snatch and chip...So the first part of the
ALMOST but not quite, just as though you were grinding a straight
cone point on
the end of your drill. Only as you approach the second third,
does your right
hand start to noticably drop..kinda "Catching Up" on the rotary
motion...increasing the clearance as it does.
In the last third of the rotaion the right hand drops quite
enough to catch the OTHER drill lip on the wheel..that lip is
quite rapidly by now.
Above all, take your time, if it helps, move the drill one degree
at a time, and
think ahead what shape or angle the next degree of cutting face
needs...Remember, you have control, and IT ain't going nowhere
'til you decide.
After a pass on one face, flip the drill in your "Bionic Darex"
DO NOT MOVE
THAT LEFT HAND!!, return to SET position and repeat, the pass on
the other face.
Having done a couple of passes on each face..it is now time to
check the results
on our homemade "Optical Comparator"
(Sorry Jim I couldn't resist!!) ;^)
Rest the center hole in back end of the drill shank, on the center
point of the
"Comparator" and use, first one and then the other drill lip to
scribe a light
line on your whitewashed (OK Blue or red dyed) surface.
You will readily see if the lines coincide..if the lips are
even..or not, as the
case may be.
Lets assume they are..Now look directly DOWN on the end of the
drill to check
the clearances. HUH? How can you check radial clearance by
looking it staight
in the face? Surely you need to look at it sideways?
Well no you don't...for once all thos interacting and confusing
angle and faces
and clearances are going to work together in YOUR favor and make
what could be a
tricky bit of metrology..quite simple. While we are looking at
the end of the
drill, we will also check that the POINT ANGLE is correct too!!!
(Ok guys, leave quietly..teenut has finally lost it!!)
No really, trust me. IF you look straight down on the point of a
sharpened, standard drill, you will see
the two cutting edges, joined by the CHISEL edge which crosses
over the web of
the drill The angle fromed by the chisel edge to each cutting
edge, should be
ABOUT 50 deg...anywhere between 40 and sixty is ok for a first
attempt. (I can
hear the purists and theorists screaming and lighting up their
But believe me, get it in that ball park and your drill will CUT.
If the angle
is too steep..you don't have enough clearance...negative clearance
will give you
an angle event greater than 90 deg. Too MUCH clerance and the
angle will appear
While looking at the end, check the point angle, How? Look
down the axis of
the drill at the cutting edges. Are they straight? If so, your
point is pretty
close to the right angle (As designed for that drill, by its
he set the helix angle and the cross section of the flute) If the
CONCAVE the point is too flat and if they appear CONVEX, the point
If your drill passes all these tests, which take but a second or
two to perform,
THEN IT WILL CUT..pretty close to size, without chattering,
overheating, wandering or seizing. I guarantee it!
Hey, thats a pretty good start for the first drill you ever
ground! All it
takes now is a bit of practice for it to become second nature and
almost as easy
with a little 'un or a big 'un!
My apologies for "goin'on" but If it helps just one person to
pluck up the
couragre and go hand sharpen his (or Her) first drill, by hand...
Then I hope you will bear with me.
It is late, I am tired and I am not even going to proof or spell
Keep the whole world singing . . . .
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