I recently discovered how to fix an issue with drilling that I was having... I wanted to drill at a fairly slow speed in certain materials and found that one type of bit worked best. Unfortunately, they don't make that bit in letter sizes, which I need. Through experimenting, I've realized that the reason why just this one bit brand/type works so well, is how they designed the angle on the tip. Not the point angle that is generally spoken of, such as 118 degrees or 135 degrees... but the angle at which the tops are cut at. I'm not even sure what you call that part of the bit. But if you look at the bit from the side and see the main point, which is typically the standard 118 or 135 degrees... then turn the bit to the other side and look at the angle that goes along the top of that side... This is the angle the controls how much bite the blades (if that what's they're referred to) make into the material. I noticed that, that 'blade' angle on the bits that work well for me are particularly flat compared to most other bits... There's very little angle/bite at all. So... My question is, does anybody know of a sharpener that isn't a fortune, but can control that angle? Or is it possible to find human-beings these days that actually know enough about sharpening to understand that? I would like to sharpen numerous bits to that configuration.
I'll bet somebody here has the wonderful instructions I once saw here. I think it was by "T-Nut". In any case, learning how to sharpen your drill bits by hand is worth the time and effort. The first step is to have a grinding wheel dressed as close to perfection as possible. The rest is common sense and a bit of practice. Don't over heat the steel! Once you learn the basics, you can grind specials, like the one you mentioned with the low rake angle. You can be an expert in an hour!
If I understand correctly, you're thinking of the drill cutting relief angle. My Darex M5 can set this. It cost me $160 at an auction. I haven't watched but they may bring slightly more on eBay.
On Sun, 13 Apr 2008 17:29:31 -0700 (PDT), with neither quill nor qualm, Dave99 quickly quoth:
If you're saying what I think you might be saying, the angle is called "lip angle". If you set the bit down on its cutting edge, it's the clearance angle from the cutting edge to the back of the edge, right? A high angle there would tend to parallel the twist from the back, so you want a low angle.
You can sharpen them by hand that way. Never having used a drill bit sharpening machine, I don't know if that angle can be set or not.
You could also give the point angle less than 118 degrees by holding it to the grinding wheel at a lesser angle, but I think it's the lip you're talking about.
-- Save the whales! Trade them for valuable prizes.
I think that he's talking about a "dubbed" drill bit -- near zero rake -- good for drilling in materials like brass and some plastics. And this is normally done by hand after sharpening the bit in the normal manner.
Right... I did some searching and I've now seen it referred to as "Drill Lip Relief Angle". So 'Relief Angle', 'Lip Angle'... I guess all the same thing, right? All I know is that all the ones I've tried with a sharp angle there don't do what I want, and the couple I have that have the very modest angle do... So that must be the difference.
The original Darex Drill Doctor will grind non-standard relief angles if you don't align the bit correctly in the setting fixture. The angle of the center ridge to the cutting edge is after-the-fact evidence that the bit rotated in the collet but there isn't any way to control it.
I have been thinking about how to make a separate setting fixture with an adjustable positive stop for the cutting edge. Has anyone else made one that worked well?
Another point to remember is all drills drill an over sized hole, or so I was taught in machinist school. You can use this to your advantage by doing it on purpose. It is accomplished by grinding one side slightly longer that the other. Drill scrap to verify the finished hole size.
The angle you see when you hold the drill, at the tip, from one lip to the other, is the lip angle. The amount of drop behind the cutting edge when it is cutting, is the relief angle,or clearance, and the angle on the front of the cutting edge, in relation to the material, is the rake angle.
All three can be modified to some extent to improve (or not) a drills cutting characteristics.
If you can find an Industrial Arts textbook there is a better than decent chance that the various angles are explained, with a decent diagram.
For average use, 59 degrees per side (118 degrees included angle) has been settled on as the "best", but depending on the material, anywhere from 30 degrees per side to 70 per side are around.
The relief or clearance, controls the maximum amount of material that the drill can cut in a revolution, and the rake is adjusted to adjust for the material, as much as it can be, whithin the limits of the helix angle of the bit.
Some of the older Popular Mechanics Shop books had some really usefull diagrams for drills, among other usefull info.
Karl reposted Teenut's bionic system smoe time ago and I saved it again. was lost somewhere on a dinosaur model computer. Thanks Karl repost
next line emphasised, I, and others, miss Teenut's advice.
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 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..until 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..Though 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 straight 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
=================================
This post took a bit of cleaning up after all the extra linefeeds added over umpteen computer systems. I hope I haven't botched it.
I use Teenut's system and it works for me. I usually pile up blunt bits until there are about 50 of all sizes to sharpen, then do them as a batch, the last is always much better than the first, so I usually go over the first ten to improve them.
I think that all of Teenut's postings are archived somewhere. Does anyone know where I can find them ?
I was in Sears over the weekend with time to kill. They had several models of Drill Doctor on sale at a significant discount. The 500 had several features I didn't recall from the original model, and they were sold out of the 750, so I couldn't see what sort of features it had that would warrant the higher price. It looked like they had added several adjustments to the 500, which could be good or bad. More stuff to fiddle with & misalign, but in theory you can fix stuff you don't like.
Just out of curiosity, why not learn to sharpen the drill by hand? I learned when I was 14 years old and it couldn't have been that complex if a 14 year old kid with a different type of drilling on his mind could master it -- sure wish I could have mastered some of those girls I was thinking about :-) Bruce-in-Bangkok (correct email address for reply)
This is a fine article by teenut but I have said it before and I'll say it again now, switch RIGHT for LEFT and then it'll work as described! That's my opinion and I'm sticking to it......... phil kangas
It's pretty easy to learn how to hand sharpen a drill and lots of advice on this has been posted.
BUT this can produce, at best, a drill that cuts well and produces a hole that is oversize by a variable and uncontrolled amount.
A drill can only produce its nominal size hole if the drill point geometry is precisely symmetrical. It's reasonably easy to come close to with a well designed drill jig but nearly impossible with a freehand drill grind.
Can you gaze at your freehand sharpened drill point geometry and be sure that your efforts have produced a point with asymmetry less than 0.005"
Even this degree of asymmetry will produce a hole of up to +0.010" on nominal.
On Tue, 15 Apr 2008 17:38:48 +0100, pentagrid wrote: ...
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I'm sure the answer to that question is yes. 0.005" is easy to see by eye. For example, if someone hands you a #11 and a #12 drill bit, about .002" different, you don't have any trouble telling which is larger, do you?
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