Keep to the point

Sharpening drill bits can extend their lives and cut costs.

by Kay Falk

It used to be that dull drill bits were put to rest in tool drawers, seldom to see the light of day or productive work again.

If contractor tool specialists were brave enough to try sharpening them by hand, they could produce too much heat and anneal the drill bit’s edges. These annealed edges lose their temper, so they are softer than normal and will fail quickly when drilling most metals.

Mechanized sharpening solutions include $250,000 cutter grinders. That’s what large sharpening services and machine shops use, and they can do the job well.

There are also low-cost bench grinder attachments that some contractors employ for basic sharpening that can give inconsistent results.

Before 1997, contractors faced sending bits to professionals to sharpen, attempting to sharpen them with crude guide tools or pitching them.

But then, a more precise and less expensive option became available in 1997 with the introduction of the Drill Doctor sharpeners, says Dan Dovel, product engineer, and Matt Bernard, marketing assistant, at Professional Tool Manufacturing.

30 years experience in one tool
“Drill Doctor is the culmination of 30 years of drill sharpening,” Bernard says. “It evolved out of a line of industrial drill and end mill sharpeners manufactured by Darex Corporation since the 1970s. The Drill Doctor line uses the same patented sharpening technology as the Darex industrial-grade tool sharpeners.”

Dovel explains the machines work in a two-step process. “First, the drill bit is aligned in a chuck to establish the position of the new cutting edge,” he says. “Then the chuck feeds the bit through a 3-D path into a grinding wheel to produce a new cutting edge. This takes the art out of sharpening a drill by sweeping a path much like the factory uses to grind the drill in the first place.

“The feed rate is limited to ensure that the drill retains its material properties so annealing or hardening does not occur. The controlled feed only removes a few thousandths of an inch per sharpening. The machine doesn’t require special techniques by the operator,” he says.

Picture a pencil
Just as a pencil can be sharpened until it’s almost down to the eraser, the two sharpening experts say the Drill Doctor bit sharpener can keep bits sharp much longer than what is considered normal bit life now.

The number of times you can sharpen the bit depends on your bit’s length and how much material is taken off during each sharpening. “More material is removed to reshape and sharpen a broken bit than just to touch one up, of course,” Dovel points out. “That being said, an average drill bit that is 5" long may be resharpened between 1,000 and 2,000 times. In our test lab, we’ve used the Drill Doctor to sharpen a drill bit until there was virtually nothing left of the flutes.”

This ability to keep bits sharp lets contractor crews use them longer and it doesn’t take much of a worker’s valuable time. “The machine can resharpen a dull bit in less than one minute,” Bernard says. “In one afternoon of sharpening a drawer full of old bits, it can pay for itself.”

According to Dovel, the Drill Doctor sharpeners are equipped with a diamond sharpening wheel which enables them to sharpen high-speed steel, cobalt, carbide, TiN-coated and masonry bits.

He admits the machine can’t sharpen every bit. “There are a few specialty types of drill bits that aren’t easily sharpened,” Dovel explains.

“The Drill Doctor is designed to sharpen the most common drills including twist drill and masonry bits. All models in the line produce the industry standard 118-degree point angle. Some models also include settings for 135-degree point angles and split points.”

Sharpening and quality impact life
To assure the longest productive life from drill bits, the experts encourage contractors to sharpen bits often. “This allows you to remove smaller amounts of material more often, while always having a sharp bit handy,” Dovel says.

“Higher quality bits also make a huge difference,” Bernard adds. “It is tempting to buy less expensive bits. With the capability now to use a bit for many months or even years, the advantages of a quality bit far outweigh its higher initial cost.”

Drill experts suggest these tips for longer drill bit life:
1. Use the right tool for the job. Standard high-speed steel bits are an excellent choice for most materials, but some building materials such as concrete fiber siding require coated or carbide bits to attain reasonable edge life.

2. Use the correct feed and speed. It’s easy to overheat a cutting edge with the wrong feed or speed.

3. Use a cutting fluid in hard metals.

4. Avoid heat buildup. A sharp bit produces less heat, and less heat means longer edge life.

Published in the July/August 2005 issue of Contractor Tools and Supplies magazine.

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