Tool sharpening in general

In the past, I had done some metal working on a nice little mill
drill, and, at the time, I bought some carbide insert end mills.
Well, these little things cut beautifully though the length of my
project.
Now (some time later), I am without that little miller, but working on
another project, and it has ocurred to me, primarily from the number
of times that I have made my drill bits all colors of blue, that I
have not been giving feed rate and tool sharpness their correct due.
I am no longer cutting on carbide blades, usually HSS or some kind of
cobalt coating. I am cutting too fast, too hard and after the first
usage, on a dull edge.
My question regards sharpening a scraping cutter in specific, but I
think it can be extended to drill bits in general (I hope).
I have a bench grinder with a course and fine wheel, and I can form
the tool correctly on the course wheel, and touch it up on the fine.
However, the postings I have read indicate that for the final "razor
sharpness" state, I should be honing on an arkansas stone. When I
look at the blade after the fine wheel, I can certainly see the
abrasion marks. The good news is that running my finger tip over the
blade, it feels sharp.
So, I try to hone it up a bit on various of a bunch of "Mold and Die
Maker Polishing Stones" that I have. This assortment ranges in grit
from 240ish to about 400, and there are several types available. The
trouble is, after my "honing", my blade feels significantly duller.
By means of process, I pass the blade over the stationary stone some
number of times (50, 100, or so) exerting good down force, and not
moving side to side too fast (from what I can tell from the piece of
crap machining book I have, this is OK). I seem to get nicer "cuts"
from the blade after the grinder than after the honing (and I still
hesitate to call these gouging-marking-scarring-things real cuts, and
of course the cuts have all the ridges that are visible in the tool,
but the cuts are shiny are generally well-formed).
The end result of my cutting is what you think it might be, scarred
and scratched. Can anybody serve up some advice? Basically, what I
want to know, is can I get there from here - or am I lacking some
basic tools, like the arkansas stone? ...or maybe its just a lack of
experince... I know this group is quite good, and as an aside, it is
pretty cool to read posts from the mid-90s. Of course almost all of
the web-sites referenced are dead links. Good advice is timeless, and
I'm hopin' to get me some. Thanks in advance from one of the only
metal working hobbyists in ever-colder Barcelona, Spain. --ss
Reply to
ss
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In memoriam...
Subject: Re: drill sharpening FAQ? From: Robert Bastow Date: Mon, 11 Oct 1999 07:59:04 GMT
Intro snipped.....
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 finger tips LIGHTLY together..Relax the other 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 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 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 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 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 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 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 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
Reply to
TeeNut in heaven
Ok then, I've followed the technique set forth by Teenut and I only get one lip to cut. I ran into this problem the other day on a 1 1/8" drill bit. Is there a secret to getting the things ground so that both lips cut during the drilling process. As near as I could measure with my drill gauge the cutting edges were at the right angle and the same length. The chisel point was at the correct angle. I ended up cutting a bit to watch the cutting action then grinding the cutting edge till both edges were cutting about the same. lg no neat sig line
them..untill
Reply to
larry g
Odds are you are rounding the edge over and it doesn't matter if it is sharp enough to split hairs if the edge doesn't contact the work. Try inking up the ground edge with a felt tip and giving it just a few light honing strokes. Stop rocking the tool or the stone, if you need help glue the stone to a stick of wood 2' long and any rocking motion will be apparent.
Reply to
Beecrofter
Man I hear ya. The only way I can get both flutes to cut the same is by trying the drill and then grind a little more off the edge that's cutting harder. The difference here is only a few thou.
I built a drill grinding attachment for large drills to solve this problem. Its easy to touch a perfect drill up by hand when it dulls a little. The biggest help with a perfect drill is keeping the holes from drilling oversize - when one flute does most of the cutting it forces the drill sideways and you get a larger hole.
Where my son used to work, they'd send out drills for professional resharpening. The after the drill has been touched up several times, send it out again. A good sharp drill allows higher feeds and speeds on CNC equipment. Plus, some of the operators weren't very good hand drill sharpeners.
Karl
Reply to
Karl Townsend

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