Howdy folks. As I continue to install doubled steel "french" doors in a steel frame to close the hole I cut in the back wall in order to insert the bridgeport mill into the back bedroom I am beginning to dull all my drill bits drilling holes into the channel iron and wood framing.
A 5/8" drill bit costs a significant amount of money. Since I'm not even good at sharpening knives I have serious concerns about whether I have the equipment and/or a steady enough hand to re-sharpen these bits.
I'm generally aware of the "geometry issues" that go with re- sharpening bits. But how DO you do it by hand? Is it a free-hand operation? Or do you use some kind of guide or fixture?
Vernon fired this volley in news:1a0ddf0f-2095- snipped-for-privacy@e25g2000vbe.googlegroups.com:
Vern, for small bits, (say) a 1/4" diameter or less, I use a decades old Craftsman bit grinding jig. It mounts on the bench to the side of a grinder, and trims up the edges against the side of the wheel.
For larger bits, unless I'm doing some relatively high-precision drilling (which you are NOT), I freehand them, because it's much faster, and pretty easy to master.
I think establishing the back rake is the hardest part to understand and see properly. Centering is dead-simple.
Lloyd, thanks for the encouragement. As you well know, the cost of bits increases exponentially with the size. So my concern is keeping the 1/2", 5/8", and 3/4" bits alive. I don't remember how much I paid for the last 3/4" bit I bought but I do remember that the price made me cringe. At this point they're getting so dull that they're worthless anyway. So I guess I can't screw 'em up! V
------------- Yes you can do it free hand, but it takes a fair bit of practice.
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but also take a look at
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I have one of these and it works pretty good. I set mine up to use the disk on my 4X36belt/6disk sander.
There are Chinese copies of this available that are somewhat cheaper.
Not as easy or quick to use as a drill doctor, but about 1/3 the cost.
Drill Doctor is the top of the line hobby drill sharpeners.
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{extra cost large chuck required or see}
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split points.
Another alternative if you have several dull drills, is to contact a local sharpening service to see what they would charge. Frequently the shop that does saw sharpening also has a drill pointer in the back. Generally pretty cheap if you don't require rush service and do the drop off/ pick up yourself.
Unka' George [George McDuffee]
------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Vernon , when I do this , the best description I can give is "lower the free end as you rotate the tip against the grinding wheel " . The biggie is to have the heel of the lip shorter than the cutting edge . With a very little practice the big ones are much easier than tiny bits . Having a flat true surface on your grinding wheel is probably the biggest thing , and a light touch comes a close second .
What the others said about sharpening! I just free hand mine. The 'drop as you turn' thing works. Take a look at a properly sharpened drill (any larger size is fine). When you look at the drill from the side, the ground area should drop away at about a 10 degree angle. Most common mistake is to get a cutting edge with no relief.
You didn't ask but you should NOT have to resharpen for a single project. Most common mistakes on large drills is running too fast and with too little pressure. If you are using any sort of portable drill I can almost guarantee you are not applying enough pressure. I have an old
1/2" portable drill that turns 200 rpm. I rig up a strap/chain with a
2x4 through the 'D' handle, get about 4:1 leverage to put enough force > Howdy folks. As I continue to install doubled steel "french" doors in
Excellent point on the pressure. Which is what makes a drill press so efficient.
re speeds: according to
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a .625 drill should be about 500 rpm, which is probably what most drills will slow down to, with suff. pressure. Oil will help quite a bit in preserving bit life. Smoke indicates the oil is doing its job.
What happened with the 5/8" bit was this. I was doing just fine using a cordless Porter Cable drill. But when the battery gave out I switched to a new Bosch drill that I just got yesterday. The Bosch drill seems to run much faster than the older Porter Cable. So I clumb the ladder with the new drill to finish the hole. I was up high which made it hard to exert much pressure on the bit. Plus the drill was turning too fast. Before I got things under control I had lost the edge on the bit.
That's a nice simple formula. Rearranged, max bit diameter D =3D 90 / (RPM*.26) so the 400 RPM Bosch is OK up to 0.865", ~7/8" or 22mm.
I always work from scratch, D * pi =3D circumference, * RPM =3D inches per minute, / 12 =3D feet per minute, because I don't trust myself to remember formulas without intermixing similar ones. This one amounts to the diameter times one quarter of the speed, easy mental math and close enough for the go / no-go accuracy required.
You can grind away the metal behind the cutting edge until the end resembles a spade bit, then sharpen that without rolling it. Watch the angle of the center ridge, which indicates back relief, and try to make it the same as a new bit. This isn't as good but it's a lot easier for a beginner. You don't need to make the point angle 59 degrees, a wide range of angles works well as long as both sides match. When you buy a drill sharpener, clean these up to ~59 degrees by hand so you don't wear down the grinding wheel in it.
The grinding method you describe below creates very effective cutting edges, Jim.
It's a 4 facet grinding method, which is essentially the same as most split-point drills.
The 4 facet points aren't just an easy method of resharpening for beginners,
4 facet points are produced for many manufactured drills. These points greatly reduce the amount of feed force/pressure required for drilling, particularly helpful when drilling with a handheld drill motor.
When viewing the brazed one-piece inserts of carbide-tipped masonry drills (for example), one can easily distinguish the 2 facets. The webs of HSS twist drills are wider, and the 4 facet grinding method results in a very similar cutting area on/at the drill point.
The disadvantage is that the bit is more likely to chatter and drill oversize until the intact flute sides enter the hole to stabilize it. But it will keep you going when hole size isn't critical.
Vernon, my dad was a lifelong machinist, and a flight engineer in the USAC during WW2. He was good. He'd take one of those 1" x 3" Arkansas whetstones, and sharpen drills whilst humming all the way. It took him less than a minute on some, longer on others. Boy, they would cut!
Myself, he never taught me that. I bought a Drill Doctor 750 at a trade show a few years ago. It sat in the closet for five years. Recently, I got it out, and I'm sold. I must have 800 drillbits, 789 of them dull. I still buy them at yard sales by the handfuls to have sharp bits. Now, I need to take a full day and sharpen and index them all. A winter's day thing.
Consider a drill doctor. It's nice to do by hand, and I'm sure you could learn or be taught.
My dad's action looked mostly like the rolling action of both wrists at once like turning a plastic bag inside out with two hands.
Steve. What a great story. Since I don't have a grinder and do have a whet stone I will give 'em a whirl. I will be thinking about your dad while I hum.
Vernon, Let me introduce you to one of the best contributers to this Newsgroup...his name was Robert Bastow and his handle was teenut. He died some years ago of cancer the article below was his answer to your question posted in 1999. Steve
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,
Gentlemen. I figured things out yesterday about Robert Bastow a/k/a "teenut". I also found the memorial page that his wife set up. I hope when I pass on that somebody, somewhere, remembers me with such affection. Best holiday wishes to all. Vernon
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