Subject: Re: drill sharpening FAQ?
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 the
angle as equal as possible on both sides..I'll tell you how to do THAT in a
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 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
same mental picture of what I am describing. We approach the wheel, which
been dressed on its face, dead straight across with no grooves..(Ve SHOOT
ve catch putting grooves in ze drill wheel!!..No Pity..No Prisoners..Ya!
The drill shank is held firmly in the RIGHT hand...ALL the movement and
is imparted by the RIGHT hand. For the purposes of drill grinding, the left
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 other
three fingers aand let them naturally curl against the palm of your hand.
the drill flute drop into the vee between thumb and fore finger and let the
of the finger "Find" the curve of the flute where it fits comfortably. The
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!
Lift the drill from your fingers...see the GROOVE?...Drop the drill back
locates within a thou or two! Magic?..Bionic at least! Squeeze again to set
groove. You have created a customised drill guide that fits better that
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
Place the knuckles of your left hand, LIGHTLY on the ginding wheel tool
and swing the drill shank, from left to right (using ONLY your right hand)
push the drill lengthways though that groove in your fingers back or forth
the groove to make the drill twist or "rifle" in your fingers. Do NOT move
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
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 ensure that
your soon to be ground drill lip will start with a "smidgin" of cutting
(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
center of the wheel)
C) The two cutting edges of the drill..the straight, sharp bits, formed by
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
hand..the othe sharp bit of course, pointing downwards (Jeeze this would be
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
exercise. GENTLY ease the cutting edge towards the spinning wheel,
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
You will hear a subtle but distinct change of tone JUST, I mean Just...a
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
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
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
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
take up that last couple of tenths and the wheel begins to cut. Let it
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" are
in control of that drill and the wheel..Forget the times when, close to
you swung the drill wildly past the wheel, hoping to get "the dirty deed"
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
the hour on a clock face, to roughly 25 minutes past. But it isn't a smooth
of a circle, more a sector of an elipse..You see, as your hand starts to
slowly, you are also rotating the drill in "the groove"..the first third of
turn needs to maintain that very slight clearance angle on the cutting edge,
not increase it too rapidly.
You need the clearance to cut..But too much at that point will WEAKEN the
and cause the drill to snatch and chip...So the first part of the rotation
ALMOST but not quite, just as though you were grinding a straight cone point
the end of your drill. Only as you approach the second third, does your
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
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,
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
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
Having done a couple of passes on each face..it is now time to check the
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
"Comparator" and use, first one and then the other drill lip to scribe a
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
case may be.
Lets assume they are..Now look directly DOWN on the end of the drill to
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
and clearances are going to work together in YOUR favor and make what could
tricky bit of metrology..quite simple. While we are looking at the end of
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
the drill The angle fromed by the chisel edge to each cutting edge, should
ABOUT 50 deg...anywhere between 40 and sixty is ok for a first attempt. (I
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 the
is too steep..you don't have enough clearance...negative clearance will give
an angle event greater than 90 deg. Too MUCH clerance and the angle will
While looking at the end, check the point angle, How? Look down the axis
the drill at the cutting edges. Are they straight? If so, your point is
close to the right angle (As designed for that drill, by its manufacturer
he set the helix angle and the cross section of the flute) If the edges
CONCAVE the point is too flat and if they appear CONVEX, the point is too
If your drill passes all these tests, which take but a second or two to
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
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 check this,