View Full Version : sharpening drill bits

02-25-2004, 06:44 PM
saw this on home machine shop, thought some would like to see it.
Anyone who wants to learn this skill should start large - and I mean 12 inch and above. This is a great way to make long drills short.
I believe I learned on a 3/4" taper shank drill..it is a lot easier to
see all the angles and begin to understand how they work and interact.
By the way..we had a handy little dohickey to help get the drill lips
level. I have never heard it described before..
For the morse taper shank drills from 1/4" up to about 1" diameter, we had a piece of 2" by 1/8" hot rolled steel strap..about 14" long. One end was bent at right angles, about 2" from the end to form an L shape with one 12" upright and a 2" horizontal. In the geometric center of this short leg was afixed a "dead" center..not a lathe tailstock
center!!...more like a 1/2" bolt, 1/2" long, turned or ground to a 60 deg point (Approx...no great precision required) and screwed in from the under side. Thats IT..toolmaking over!

In use the inner face of the upright was coated with whitewash (Never
SAW marking blue 'til I got in the toolroom!) The drill was ground,
freehand, on the FACE of the wheel (not the flat side)...care being
taken to keep the POINT angle as equal as possible on both sides..I'll
tell you how to do THAT in a moment..

Lets do that now in fact..

Jim, You are dead right about not being able to grind a drill without mechanical 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 drill..it is 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 groovesThe 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 forefinger tips LIGHTLY together..Relax the other three fingers and let them naturally curl against the palm of your hand. Let the drill flute drop into the vee between thumb and forefinger 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 smoothly the 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
tool rest, 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 nature.

B) The drill axis is dropped JUUUst below horizontal. This will
ensure that your soon to be ground drill lip will start with a
"smidgin" of cutting clearance.

(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), should be horizontally disposed..with the edge uppermost on the side closest to your left hand..the other sharp bit of course, pointing downwards (Jeeze this would be a lot easier with a sketchpad)

This I will call the SET or START position!

NOW, move your left hand for the first, last, and ONLY time during
this whole exercise. GENTLY ease the cutting edge towards the
spinning wheel, carefully maintaining all the angles and orientations of the SET position..until the cutting edge is JUST shy of touching the wheel. If you listen carefully you will hear the tone of the entrained air, whistling through the narrowing gap. You will hear a subtle but distinct change of tone JUST, I mean Just...a couple tenths
of a thou BEFORE the edge touches the wheel. STOP!!! FREEZE!! DO

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
grinding rest is otherwise quite relaxed..letting the drill slide,
twist and tilt wherever 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 clearance, and cutting angles, and rakes and......

With the RIGHT hand in control, gently, kinda, lean forward... bending or squeezing your arms hands and body..rather than actually moving them..untill you take up that last couple of tenths and the wheel begins to cut. Let it cut..don't force it, and don't rush it..it really won't hurt anything if you take a full minute per pass per face. YOU and your "Bionic Darex" are totally 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 trying to generate. Just the one face is left to "Interpretation"...every other aspect,angle, facet, what have you...Has ALREADY BEEN TAKEN CARE OF!! and is locked in place under your control!

The right hand should perfome 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 rotation is 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
rapidly..Thogh not enough to catch the OTHER drill lip on the
wheel..that lip is coming around 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 those interacting and confusing
angles and faces and clearances are going to work together in YOUR favor and make what could be a tricky bit of etrology..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 well 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 flame throwers.) 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 too shallow!

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 manufacturer when he set the helix angle and the cross section of the flute) If the edges appear CONCAVE the point is too flat and if they appear CONVEX, the point is too "Pointy"

02-25-2004, 06:45 PM

Mike W
02-26-2004, 08:07 AM
Here is a site that has more info: http://www.newmantools.com/machines/drillpoint.html

02-27-2004, 10:35 AM
I will need to go over that a few more times befor it begins to sink in. mental overload, but thanks for the great read.

fla jim
02-27-2004, 11:49 AM
By the time you guys get done reading all this. I sharpened an index full of bits on my "Drill Doctor::laugh:

Mike W
02-27-2004, 02:52 PM
Some of us just like to split hairs or would that be points? :D I have done a whole coffee can of drills in the time some people write in talking about why the Drill Dr. is no good. :rolleyes:

02-27-2004, 03:06 PM
Originally posted by fla jim
By the time you guys get done reading all this. I sharpened an index full of bits on my "Drill Doctor::laugh:

Jim, you only have 2 drills in that index cause you ground the rest to nubs with the Drill Dr. Dogzilla ate all the rest of the drills in the coffy can for iron suplements.

fla jim
02-27-2004, 03:33 PM
Franz see what you've gone and done now!:nono:
You've embarrased him.
Actually when he gets excited he drools excessively. I bought the Chi-com blast cabinet to get the rust off of my stuff.

02-27-2004, 07:17 PM
I Figure that with enough practice and a little guidance anyone is capable :D

fla jim
02-27-2004, 08:12 PM
Did you get him from the OCC shop? Some of their work pratices look like it's done by dogs.
Where's his safety glasses?:nono:

02-28-2004, 12:06 AM
Yeah, I saw that after I posted it.. Chewy(the dog) has been punished accordingly.. No cookies tonight.

02-28-2004, 12:53 AM
Originally posted by Brainfarth
Yeah, I saw that after I posted it.. Chewy(the dog) has been punished accordingly.. No cookies tonight.

:angry: HEY lets remember our paw-lick-tickle correctness, it ain't dog, it's Canine-American! :blob2:

02-28-2004, 02:33 AM
And another thing, you younguns don't know squat about grinding. Here's a picture of some real grinding like us Old Farts do.:cool2:

02-28-2004, 02:40 PM
yee dawgy! ride that puppy...

02-28-2004, 03:07 PM
Say Brain,

I've been trying to get my Pit to help out around the shop, but have been unable to talk him into it. Got any tips? How old is yours.

02-28-2004, 04:01 PM
He's almost 6. But half of him is brendal pit and the other half is sheppard. I think that's where he gets the agility to rotate the bits at the correct angles. As for talking to him, It's the cookie bones that do all the talkin'. ;)