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View Full Version : Sharpening Drill bits, a engineers method



ibewgypsie
02-22-2004, 04:03 PM
Kurt Laughlin wrote:
<snip>
> I am neither a machinist nor even an operator. I'm an engineer (no
> calluses, all ten fingers :-)) who bought a small lathe and a mill-drill to
> play around with. Hand sharpening is beyond my skills, a machine sharpener
> beyond my budget, so I pay a guy to do it just buy new ones.

Once someone showed me the tricks it was pretty easy. But I don't hand
sharpen small drills (< 3/8"?).

Hold the drill in your left hand, the front side of your finger gently
touching the edge of the tool rest, with just enough drill sticking out
that it is a few thousandth's away from the grinding wheel. The cutting
edge is on the left, horizontal, and you are looking down on it.

The right hand holds the drill shank and controls infeed and the
swinging and rolling movement that follows. Gently press in until the
wheel starts cutting and at that time swing your right hand to the left
slightly, roll the drill clockwise a little, and maybe lower the end of
the drill a little as you finish the cut. The infeed is continued
enough to maintain a light cut during the entire process.

The rolling and swinging movement causes the cutting edge to move away
from the wheel as the infeed and left swing follows the relief angle
behind the cutting edge.

To practice the movement, place a properly ground large drill near or
gently touching a *non turning* wheel and make a movement that keeps the
relieved area behind the cutting edge in contact with the wheel
continuously.

It you started with a chipped point (I know, it only happens when
someone else has been using your tools), make two or three light passes
on the chipped side, then two or three on the good side and keep that up
until the chip is gone. Hold the drill up vertically towards a light
source and use a drill gage or protractor to compare the length of the
two cutting edges.

The disclaimer: Your hands, fingers and face are at some risk during
the process, use appropriate safeguards. Working around machinery is
almost as dangerous as driving on public roads or living in the world.

--

Mike W
02-22-2004, 04:20 PM
Interesting, I still think that sharpening a drill by hand is like trying to turn a shaft to a 1" diameter. The only tool you have to measure it is a ruler.

barts
02-22-2004, 05:16 PM
> Interesting, I still think that sharpening a drill by hand is like trying to turn a shaft to a 1" diameter. The only tool you have to measure it is a ruler.

Use a old 1/2" drill that is't sharp any more
but isn't too damaged to practice with... use the drill gage, and be prepared to sharpen it several times... our instructor for the machine shop classes I took had us doing this for several hours. If you do it often enough, you can go pretty small - handy when you chip the tap drill you need 10 minutes after the hardware store closes.



------------------
Bart Smaalders
http://smaalders.net/barts

darryl
02-22-2004, 05:31 PM
Ironic. Almost all the drill bits I sharpen by hand are less than 1/2 in. I routinely sharpen 1/8 and smaller by hand, and sometimes they are only .031. I keep a set of factory sharpened hss bits for when I need to get a more accurate hole, which is no guarantee, I realize. It's interesting how a seemingly mundane task turns into a bit of a black art.

Forrest Addy
02-22-2004, 06:38 PM
Fine except for a critical ergonomic consideration: Don't tip the drill down with the right hand. Lift with both hands without tipping the drill so the clearance is ground by the drill's following the wheel radius. The clearance angle comes out much better once you develop the knack.

Otherwise, Gypsie's written the best all-text account of how to free hand sharpen a drill I've even seen.

[This message has been edited by Forrest Addy (edited 02-22-2004).]

ibewgypsie
02-22-2004, 08:58 PM
Now Forrest, YOu know I won't take credit for a clip and paste job. SOmeone else authored it. I was looking for a loupe with drill point angle on it. AND there it was.

When I sharpen them like it says, I make a real aggressive bit that breaks when it pierces. They sure throw pretty curls thou.

David

aolney
02-22-2004, 09:14 PM
I thought these instructions for sharpening from the usenet group rec.crafts.metalworking was interesting.
It was written by Robert "Teenut" Barstow.

FILENAMES:

only this text file

DESCRIPTION:

This is a copy of instructions for hand sharpening drill bits as
originally posted in rec.crafts.metalworking by Robert Bastow (teenut).
Posted by Ted Edwards <Ted_E@bc.sympatico.ca>. Ted provided the
following description:

================================================== ===============
I just posted Teenut's description of how to sharpen a drill by hand
to the dropbox.

Ted

------ Teenut's instructions -----

Anyone who wants to learn this skill should start large - and I mean
1/2 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 grooves..(Ve SHOOT anyone ve catch putting grooves in
ze drill wheel!!..No Pity..No Prisoners..Ya! Verdampt!)

(Sorry)...

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 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!

UNTIL....

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 sketch
pad)

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
NOT MOVE!!

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 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 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"

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, chipping, 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!

Hey guys!

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 check
this,

'night all

teenut

Evan
02-23-2004, 03:03 AM
I had no idea that this was such an involved subject. When I was in the aircraft repair business we would walk over to the grinder and touch up the drill bits whenever necessary. Way shorter walk than going to the tool crib. Grinding drill bits by hand is not rocket science. You need a well dressed stone. Sheesh...

ibewgypsie
02-23-2004, 07:24 AM
Evan

Drill sharpening is a learned art. You must have learned. Somethings easy for some are difficult for others. With some of the complex items you post you must be good at it too.

Who taught you to ride a bike? I bet someone was there helping you.. HA..

HELP... My drill sharpening skills suck...

David http://bbs.homeshopmachinist.net//biggrin.gif

JCHannum
02-23-2004, 09:41 AM
When writing instructions for a "simple" task, we are reminded of the complexity of the operation, and the skill it takes to put it into words.
Sometime when you have nothing better to do, write up how to tie your shoes. A simple operation we do every day. It might give you an insight of what is involved in putting something like this on paper.
By the way, I have seen more than a few drills sharpened by "experts" that were far worse than anything coming out of India.