I free hand drills to as big as they make them - 3 1/2" I think - or I did when I was still working for a living. My biggest drill is 2 1/8" and I just a week ago hand sharpened it with only one good eye (cararact operaion coming up Mon 10/24). Here's from my article in the May-June 05 issue of HSM:
"The cheap drill sharpening jigs made for bench grinders sold over the years are universally flimsy and awkward to use. They would do a good job sharpening drills if the user tinkered with them long enough but who has the time when a project is burning in the heart of the home shop machinist? Real drill pointers like those made by Oliver, Cincinnati, Sellers, and others over the years are first rate items of production sharpening equipment. One man can keep a twenty man shop in sharp drills by working one of these pointers a couple hours a week.
Hand sharpening: Fancy drill sharpening gadgets aren’t always available. I grind drills free-hand even now as a blurry-eyed old guy.
If you use a common bevel square or a drill gage to get the lip angles equal and a pair of dividers to get the lips symmetrical you can do an excellent job of drill sharpening free-hand. If your skills are well developed you can free-hand sharpen drills by eye alone. All it takes is practice and some experimentation. Here's how:
Dress the grinding wheel straight across so its periphery is a near perfect cylinder.
Assume a firm comfortable stance in front of the bench grinder.
Hold the drill comfortably so the flutes cradle themselves in your fingers of your right hand and with the shank in your left. The fit of the drill in your right hand registers it when you index (rotate the drill precisely 1/2 revolution).
Present the drill to the wheel and adjust your stance so the lip is parallel to the tool rest and the angle is parallel to the wheel's periphery. If your stance is right your indexing and presentation is almost automatic. If you have to twist or distort your body your drill sharpening will reflect it. Go through a few preliminary sharpening motions to ensure the repeatability of your stance and your grip on the drill.
Touch the drill to the wheel periphery and after a second or two lift up to grind the clearance angle by following the wheel. Make the lift firmly but without haste. Do not rock the drill shank down to grind the clearance. It makes you stoop and throws off your stance, the clearance angle, and often your parallelism to the wheel face. Lift the whole drill up without rocking or rotating it and follow the drill in. If the clearance is excessive don't lift the drill so high. If the drill needs more clearance start the lift sooner.
Index the drill in your fingers to grind the next lip without thinking about it too much. Just give it a quick rotation with the hand and re-cradle it as you resume your grip. Let your senses tell you when the drill is properly indexed. You'll be surprised how accurate and repeatable these neuro-muscular maneuvers are when not interfered with by a worry-wart brain. Check the parallelism of the lip and the angle with the edge of the tool rest then immediately grind.
Grind the drill through several indexes stopping to check the lip angle, symmetry, and clearance. If all is well, good. If not, no harm is done; sharpen it some more until it’s right. Try the drill in the drill press. If you get two equal spiral chips great. If you get two unequal chips maybe not so great but if the hole is less than 0.005" over nominal you did good.
There is no need to slavishly adhere to the 118 degree included drill point angle. You need to be close but it’s more important for the drill point to be centered, symmetrical, and equal angled in its two cutting edges. Different materials might call for special cutting angles and clearances which may be found in appropriate technical references. When the need arises you may wish to grind a special point on the drill. There’s nothing to keep you from doing it except the cost of the drill (low) and the number of sharpenings the drill can endure (many) before it gets to short for use.
Smaller drills – those 3/16” and under – I free-hand sharpen with a hand stone. I might touch them up on a bench grinder but I finish them with a hand stone. It takes but a few minutes and you have much better control over the angles and other features.
Sharpening drills is a manual skill requiring practice and training of the neuro-muscular system. You cannot verbalize free hand-drill sharpening except as a means to get the beginner started. It's like riding a bicycle or catching a ball. The skill lies in the reflex loops you develop not conscious thought. If you don't do sharpen a drill perfectly the first time, don't worry about it. They make drills long so apprentices can practice sharpening them. When you sleep your brain will re-program itself and you'll do better the next day. That's what sleep is for, to rev and mod the brain’s software. Practice! Practice! Practice!
Story: I once was called in to work on a Sunday to drill some big holes to layout in a thick piece of steel plate using a monstrous radial arm drill. There were plenty of suits and white hats present emphasize the job’s urgency. The tool room was locked up but I found a chipped drill the right size (2 5/8" dia as I recall) in a drawer. I free-hand sharpened it on a big Hammond grinder judging the symmetry and the angles by eyeball alone. Some white hats drifted over and talked among themselves as I worked the drill on the grinder - one skeptic making dire predictions.
Well, I was both lucky and well-practiced at the time. When I started drilling, a pair of chips spiraled out the gullets as sweetly as if the drill was machine ground. I cranked up the feed to 0.020" per rev and did my best to slop dirty, horribly contaminated soluble oil on the critics. As senior supervisors they were experienced in the game and danced back, timing things nicely. Drilling the four holes from the solid took a half hour. De-burring and chamfering took another ten minutes. Bada-bing and it was on the pallet.
I got handshakes and congratulations from my panel of judges. I don't know why - I thought success was a lock. I was thirty years old at the time and had the eye of an eagle, was sharp as a tack, and arrogant as a newly hired prosecutor. But I smiled and nodded as I fork-lifted the piece onto a truck for the ship's force to drive it away.
My story goes to show that skills will save your bacon when you least expect them to. What would have happened to my reputation if I sniveled about no sharp drills being available? Thirty people were standing around on overtime and I couldn’t sharpen a drill? What a disgrace! I’d have been sent to the propeller shop to grind and contour blades until I retired with lungs of brass.
Thinning the web: Thinning is necessary as the drill is sharpened back. The slightly rounded corner of a grinding wheel is used to clean out the intersection of the cutting edge and the gullet. The effect is to narrow the chisel edge reducing the thrust necessary to feed the drill. The drill is held at an angle to the wheel and you sight down the corner of the wheel as you bring in the drill into contact. This is another eyeball skill you have to practice. The beauty of this technique of thinning the web is it can be accomplished on a bench grinder whose wheels have been neglected. Some long a the wheel’s corner can tuck into the gullet you can use it to thin the web.
Split points: Thinning the web until the chisel point just disappears to become a sharp intersection is called a “split point.” Do this carefully. Over-grind a split point and its benefit evaporates. It takes a keen eye, a steady hand, and a grinder whose wheel has been properly dressed to a sharp corner.
Backing off the cutting edge: The cutting edge angle at the lip is equal to the drill’s helix angle - roughly 25 degrees. This is a very aggressive hook angle and it causes the drill to grab on breakthrough when hand drilling. When drilling some soft, strongly crystalline metals (cast valve bronze for example) the hook can cause the drill to “follow the helix” right into solid metal. Following the helix is a particular problem when step-drilling to enlarge holes. This often results in a broken drill or at least the drill is snatched out of its taper twisting off the driving tang. Backing off the edge of a drill is a means of reducing this “hook” at the lip of the cutting edge making it unlikely to grab.
A slip stone (or on larger drills the side of a grinding wheel) is used to make a narrow land on the cutting edge having either neutral or slightly positive rake. The edge only has to be backed off by roughly double the feed rate to be effective. In small drills where a typical feed rate would be 0.002” per flute only a bright line is actually necessary. However, it’s customary to back off a drill to at least 1/64” land width so the modification is readily visible to the next user - more on larger drills.
Lobing. Drilling spindles are not particularly rigid, drills are usually long and flexible, and the standard drill tip geometry is a compromise at best. The result of these variables is the drill can “lobe,” that is, make three and even five sided holes as easily as round ones. If the material has sufficient thickness the drill will eventually “round up” but the wobbly entry may be unsightly. The solution may be to drill a starter hole a bit smaller than the drill’s chisel edge thickness to give it a center to work from. If the material is thin, use a butterfly drill. You can also clamp a guide bushing on the work – even a piece of plate with the right sized hole in it will serve as a drill guide. If you’re starting the hole with a center drill, next time drill only as deep as the stub. If you’re drilling with the tailstock in a lathe, drill undersized for a starter then bore the hole to size for a short distance followed by the full sized drill."
And that the truth.
There are a lot of good cnc machinists that hand off their drill sharpening.
