Sharpening Drill Bits
By Steve Hill, CO

Few things can be more frustrating to a technician than a dull drill bit. I’m sure you’ve experienced it. The job is all finished except for drilling a few holes and screwing everything together. You start drilling with your favorite drill bit, the one you’ve used time and again for the past month with great success, and it barely even makes a dent in the metal.

It had to happen eventually—you’ve used this particular tool to the point where it has gotten dull (no pun intended). You would love to sharpen it as you could a pocket knife, but every attempt to do so results in a butchered mess. So instead, you grab a new drill bit and just get the job done.

That’s expedient, but what will you do with that drawer full of dull drill bits? This month’s “Tech Corner” will give you some tips on sharpening…and how to minimize the wear and tear that leads to drill bit dullness in the first place.

Drill bits 101
Drill bits come in standard sizes, in a wide variety of types. The type that technicians use most is known as a “twist” drill bit, named in 1861 by inventor Steven Morse. It was originally manufactured by cutting two opposing grooves in a section of steel rod and then twisting it like a corkscrew. Today, with computer-numeric-controlled (CNC) machines, twist drill bits are made by rotating the rod between two opposing cutting tools. We use this bit for drilling holes through materials such as metal, wood and plastic.

The twist drill bit is comprised of several distinct parts. The part that is secured into the chuck of a drill is known as the shank. The tip comes to a conical point at the other end of the bit, which then fans out to create two cutting blades known as lips. It’s these lips that you’ll be sharpening.

You can obtain several angles of tip, but the most common angle is 118 degrees. This is a sort of all-purpose angle. You might consider a tip with a shallow angle, like 150 degrees, for drilling stainless steel, or a steeper angle, like 90 degrees, for drilling through soft materials such as plastic. Personally, I like to keep it simple and buy just the 118-degree bits.

Durability
The many different materials that can be used to construct your twist drill bit have unique properties that will affect its functional lifetime. The low-end bits are made of high-speed steel (HSS). These are very inexpensive, but they don’t last long if you’re going to use them for drilling much stainless steel.

A coating added to high-speed steel, known as TiN (titanium nitride), offers more durability. TiN is a hard ceramic coating that can prolong the life of your drill bit by at least three times. The only real downside to TiN bits is that you can’t sharpen the coating. You can sharpen the bit, but then you’ve rubbed off the coating and are back to a low-quality HSS bit. Other coatings include TiAN (titanium aluminum nitride) and TiCN (titanium carbon nitride), which are even more durable than TiN.

My personal favorite is the cobalt drill bit, composed of a different kind of steel that has had extra cobalt added during its manufacture (approximately 8 percent). Not only does it last longer and cut at higher temperatures than either the HSS or the coated bit, but you can also sharpen it without losing the hardness the way you would with a coated bit. It’s three times as expensive, but lasts twenty times longer before becoming dull (user results may vary). For my money (and I’m a cheap bugger), cobalt is the way to go.

Care and feeding of drill bits
Minimizing wear and tear on drill bits in the first place will minimize the time spent sharpening them. Technicians should keep in mind these commonly overlooked aspects of drill bit care:

•    Lubrication. The bit must be lubricated when drilling through any metals, even aluminum (though aluminum requires less lubrication). This helps the lips of the bit to cut more easily, reduces friction, and cools the metal at the same time.

•    Feed speeds. Feed speeds and spindle speeds must also match the material being cut. Drill stainless steel at slow spindle speeds. Drill aluminum at higher spindle and feed speeds to avoid galling and buildup of metal on the drill bit lips.

•    Storage. Store all of your drill bits in a special case or wooden block that protects the tips from damage. Letting them bang around in a pile inside of a box will only allow the sharp tips to chip and rub against each other, dulling them.

To sharpen or not to sharpen
When deciding which bits to sharpen and which to discard, consider their size. The smaller the drill bit, the more difficult it is to see the tip clearly, and the longer it takes to get it right. Small drill bits are also the least expensive, and it may be less trouble to just replace them. Only you can decide when it no longer makes sense to spend valuable time on the grinder. I tend to draw the line at a 3/8-inch bit.

The fine art of sharpening
It’s best to sharpen your drill bits before they get dull. They will only need a touch-up then, and you can plainly see the original intended shape of the lips.

The trick to sharpening drill bits is really quite simple. First, dress the grinding wheel completely with a sharp dressing wheel. It must be perfectly flat across its grinding edge. Any ridges will only foul up the edge of the bit.

Next, you’ll need to replicate the angle of the lips. You can measure with either a machinist’s angle or your good old technician’s eyeball. I choose the latter, but you may wish to be more exact if your eye doesn’t work as well as your micrometer.

More important than the lips being a certain angle is that each be of an equal angle. That’s the key. For example, each lip should be roughly 59 degrees, for a total of 118 degrees.

I also like to get a sharp drill bit of the same size I’m sharpening and try to duplicate that shape. If one isn’t available, just grind it the best you can and try it out in the drill press. If it still isn’t sharp, try it again. It may take a couple of tries, so don’t give up.

The method I use is very simple, but it takes some practice, fine motor skills and hand-eye coordination. You must make three motions simultaneously: While holding the shank in one hand, move the bit across the grinding stone to the left and downward while twirling the bit clockwise. If you do this while keeping the drill bit at the correct angle to the grinding wheel face, you will wind up with a sharp bit.

Since this method is something of an art form, you may find that there are good days and bad days. Sometimes the resulting bit point is good enough for drilling only aluminum, and other times it’s as good as new and can go right through stainless steel. But for perfect results each and every time you’ll have to invest in the sharpening machine.

The easy way
Drill bit sharpening machines range quite a bit in price, but can save you a lot of money in the long run. That assumes, of course, that you are willing to spend the time to sharpen drill bits. Many shops buy these machines only to have them collect dust. In order to make the machine pay its way in life, you might have to make a scheduled job of using the machine, much like you do with changing oil in the air compressor. If someone doesn’t put it on the calendar, it will probably never get done. You can buy Drill Doctor™, a popular favorite, for about $50.

Not to put too fine a point on it, I hope this article has given you a few things to think about: what kind of drill bits fit your budget and durability needs, how to take care of them, and how to sharpen them to drill another day.

Steve Hill, CO, is secretary of OPTA and CEO of Delphi Ortho, located in Asheville, N.C. and on the Web at www.delphiortho.com.