It's easy to tell if you've made a mistake, you find out when you try to
push the drill through the metal - thats how I find out.
I can't sharpen a drill bit, not for lack of trying. My father learnt many
many years ago by spending near on a full year doing nothing but sharpening
drill bits for tradesmen in the factory he was apprenticed in. He never
forgot and can almost do it without looking 60 years later.
First, my all time favorite post from TeeNut:
Subject: Re: drill sharpening FAQ?
From: Robert Bastow
Date: Mon, 11 Oct 1999 07:59:04 GMT
The drill was ground, freehand, on
the FACE of the wheel (not the flat side)...care being taken to keep
angle as equal as possible on both sides..I'll tell you how to do THAT
Lets do that now in fact..
Jim, You are dead right about not being able to grind a drill without
help! Well here's how you create your own "6 Million Dollar Bionic
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
same mental picture of what I am describing. We approach the wheel,
been dressed on its face, dead straight across with no grooves..(Ve
ve catch putting grooves in ze drill wheel!!..No Pity..No
The drill shank is held firmly in the RIGHT hand...ALL the movement
is imparted by the RIGHT hand. For the purposes of drill grinding, the
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 the
three fingers aand let them naturally curl against the palm of your
the drill flute drop into the vee between thumb and fore finger and
of the finger "Find" the curve of the flute where it fits comfortably.
of the thumb rests on the sharp junction ot the land and the flute,
inch back from the drill tip.
Now...SQUEEZE HARD!!! YOUCH!...I said it would be easier if it were
Lift the drill from your fingers...see the GROOVE?...Drop the drill
locates within a thou or two! Magic?..Bionic at least! Squeeze again
groove. You have created a customised drill guide that fits better
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
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
push the drill lengthways though that groove in your fingers back or
the groove to make the drill twist or "rifle" in your fingers. Do NOT
left hand in any way..it is made of clay remember!
A) The drill axis is "eyeballed" to be at half the required point
wheel face...You can scribe or chalk reference lines on your grinder
help you line this up..at least untill it become almost second nature.
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
radially to the wheel center and about half the drill diameter below
center of the wheel)
C) The two cutting edges of the drill..the straight, sharp bits,
junction of the flute and the back face (the only bit you grind),
horizontally disposed..with the edge uppermost on the side closest to
hand..the othe sharp bit of course, pointing downwards (Jeeze this
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
exercise. GENTLY ease the cutting edge towards the spinning wheel,
maintaining all the angles and orientations of the SET position..until
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!!
Now, press the knuckles of your lump of clay..sorry, your left hand
onto, into and around the grinding rest..establish a "Groove" on the
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 tilt
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... bending
squeezing your arms hands and body..rather than actually moving
take up that last couple of tenths and the wheel begins to cut. Let
cut..don't force it, and dont' rush it..it really won't hurt anything
take a full minute Per pass per face. YOU and your "Bionic Darex" are
in control of that drill and the wheel..Forget the times when, close
you swung the drill wildly past the wheel, hoping to get "the dirty
with as quickly as possible.
Take your time, enjoy the moment, THINK about the shape you are trying
generate. Just the one face is left to "Interpretation"...every other
aspect,angle, facet, what have you...Has ALREADY BEEN TAKEN CARE OF!!
locked in place under your control!
The right hand should perfome a "Lower Quadrant sweep" for want of a
term..An observer behind you would see your hand move from about 17
the hour on a clock face, to roughly 25 minutes past. But it isn't a
of a circle, more a sector of an elipse..You see, as your hand starts
slowly, you are also rotating the drill in "the groove"..the first
turn needs to maintain that very slight clearance angle on the cutting
not increase it too rapidly.
You need the clearance to cut..But too much at that point will WEAKEN
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
the end of your drill. Only as you approach the second third, does
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 coming
quite rapidly by now.
Above all, take your time, if it helps, move the drill one degree at a
think ahead what shape or angle the next degree of cutting face
needs...Remember, you have control, and IT ain't going nowhere 'til
After a pass on one face, flip the drill in your "Bionic Darex" DO
THAT LEFT HAND!!, return to SET position and repeat, the pass on the
Having done a couple of passes on each face..it is now time to check
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
"Comparator" and use, first one and then the other drill lip to scribe
line on your whitewashed (OK Blue or red dyed) surface.
You will readily see if the lines coincide..if the lips are even..or
case may be.
Lets assume they are..Now look directly DOWN on the end of the drill
the clearances. HUH? How can you check radial clearance by looking it
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 clearances are going to work together in YOUR favor and make what
tricky bit of metrology..quite simple. While we are looking at 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 well
sharpened, standard drill, you will see
the two cutting edges, joined by the CHISEL edge which crosses over
the drill The angle fromed by the chisel edge to each cutting edge,
ABOUT 50 deg...anywhere between 40 and sixty is ok for a first
hear the purists and theorists screaming and lighting up their flame
But believe me, get it in that ball park and your drill will CUT. If
is too steep..you don't have enough clearance...negative clearance
an angle event greater than 90 deg. Too MUCH clerance and the angle
While looking at the end, check the point angle, How? Look down
the drill at the cutting edges. Are they straight? If so, your point
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 is
If your drill passes all these tests, which take but a second or two
THEN IT WILL CUT..pretty close to size, without chattering, chipping,
overheating, wandering or seizing. I guarantee it!
Hey, thats a pretty good start for the first drill you ever ground!
takes now is a bit of practice for it to become second nature and
with a little 'un or a big 'un!
My apologies for "goin'on" but If it helps just one person to pluck up
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 check
sharpen all my drills under 3/4 on it. I batch them, spend a day
That said, I find touching up a drill to be a fairly easy to learn
skill. Starting from a broken off drill takes a lot better eye. Larger
drills are actually easier. Drills under 3/16 are near impossible. I
do drills from 3/4 to 3" by hand. I did make a fixture for grinding
these but its too putsy.
There a tool that looks like a six inch scale with a special
protrusion on it called a drill gauge that you might find handy.
It is not too hard. I never had anyone show me how to sharpen a
drill, and still can not visualize Tee Nuts method. Start with two
good sized drills. One that needs sharpening and one that is good,
preferably new. Start without having the bench grinder running and
using the good drill. I grind starting at the non cutting part and
rotating the drill so you finish grinding at the cutting edge. Now
try it with the grinder running and with the drill that needs
sharpening. Do both sides and then compare with the good drill.
Look at the drills from the side and from the end. Okay so the first
attempt did not come out right, so try again. After about ten minutes
you ought to have it right.
I line up the bit in my hands against the motor housing before
shifting to the grinding wheel.
Try to match the angle where the two ground faces intersect with a
factory-ground bit. If the rake seems questionably low see if the bit
can cut into a block of wood.
You might be able to detect the wobble of an off-center point by
rolling the bit across the mill table.
Depending upon your dexterity, it can take very little time, Ig. My
dad showed me when I was 7 or so. I watched him do it, and he
explained as he went. He gave me a large bit to try on. I bought very
few new bits when I wrenched for a living. People would give me their
broken or dull bits and I'd fix them for myself.
Three mistakes show up clearly. First, you push too hard on one side
and the point is then visibly off-center. Second is if you get the
angle wrong and it just won't cut anything tougher than butter.
The method I use, which is probably typical:
1)Don goggles and gloves. Bits get hot, so have a cup of water nearby.
2) Start the grinder, belt sander, or disc sander. On a grinder, I
usually grind bits softly, so I use the side of the wheel. (Luckily,
one has never exploded on me.) It's usually quite a bit smoother and
some guides aren't easily removable. You need space for your fingers
near the wheel. A 120 or smoother grit belt works wonderfully, too.
3)Hold the bit in your fingers at an angle which makes the cutting
surface of one flute parallel with the wheel surface, with the cutting
edge (lip) facing upward. (59 degrees for standard 118 degree bits)
Now touch the lip to the wheel until it is sparking evenly. As it
touches, push in lightly lifting the tip of the bit upward, making the
grind progress along the cutting face of the flute. (Alternatively,
you can rotate the bit through that arc.) You want the back of the
flute land to be about 15 degrees lower than the cutting edge. The
grinding part should take less than a second to do for each flute. Do
one side, rotate the bit 180 degrees, and do the other side. Now dip
it in water and look at it/feel it. Is it sharp, centered, and have
the relief you need for drilling? Good, you're done.
See? That wasn't hard.
Experience is a good teacher, but she send in terrific bills.
-- Minna Thomas Antrim
Suggest a smaller diameter relatively fine grit wheel--#180 and about 1/2 of
the max diameter that your grinder can ordinarily handle....as to hardness,
a small amount of wheel wear is normal in use and IMO a softer wheel is much
better than one that's too hard--aside from possibly overheating the tool,
you don't want the wheel to be so hard that quick and accurate dressing
becomes a significant problem.
Karl, Larry and all, thanks. The above link is mine. I pulled this M2
from the "Look at it later" pile. I will try it out on a few drills.
I will also try free handnig. I think that all I need is a few hours
of time spent on this.
The motion is similar to shoveling.. the fingers holding the approx center
of the drill remain stationary, while the grip at the back end causes the
tip to kinda scoop upward, while turning to the side (as in rotating the
shovel handle to dump the load).
A small drill chuck used at the back end of the drill serves as a good grip
with a somewhat better rotational resolution/feel than the bare shank.
A common bench grinder generally works fine. Good lighting and/or a
magnifier can be very helpful.
The wheel edge should be freshly dressed flat and sharp. For wheel
types/designations, see Harold V excellent description.. PDF file available
here as Tool Grinding by Har..
Or, in Harold's numerous detailed discussions of lathe cutting tool methods
on the Chaski forum.