Just as a chain is only as strong as its weakest link, today's high-technology machine tool can only perform to the level allowed by the tools it is driving. Most people would agree, but few recognize just how much a change at the cutting edge can improve a machine's performance and lower the cost of machining.

The common twist drill is a case in point. On average, manufacturers devote half of all machining time making holes. Secondary hole operations like center drilling, reaming, tapping, boring, grinding, or honing consume up to 25% of the hole-making time. Despite being one of the most basic tools in metalworking and the key to productivity in hole-making, the twist drill is one of the most overlooked ways of unlocking pent-up profits in today's advanced machine tools.

ISO certification. however, is forcing users to look at drill points again. As global pressures intensify, more companies are finding that greater performance in holemaking is one of the fastest, most cost-effective ways to increase product quality and reduce costs.

The wheel and drill make contact via these three axes of motion simultaneously. The drill rotates about its axis (1) to put the point on its center. The drill's vertical rise (2) forms the chisel, and its horizontal infeed (3) forms the relief.

One such company is Cashco Inc. (Elsworth, KS), a manufacturer of control valves and regulators for the chemical and petrochemical industries. The company drills hole diameters from 1/16 to 3" (2-76 mm) in cast iron, brass, Alloy 20, Hastelloy, and all 300 and 400 series of stainless steel.

In the course of sharpening its own drills for 20 years, Cashco had been facet grinding conventional points on drill sizes through 3/4" (19 mm) diameter and grinding helical points in 3/4-3" (19-76 mm) drills. The company sharpens 150-200 drills per day on average.

The impetus for improving the holemaking process was to meet ISO 9000 certification. "We needed to control hole size so we could know what to expect in consistent hole quality," explains Gary Wallert, industrial technician. "We ran tight tolerances of +0.002, -0.000” (+0.05, -0,000 mm) per finished hole. Uniformity is a must for our ISO 9000 certification."

Lack of uniformity occurred in the past because the drill grinders could not maintain a point on the drill's center. As a result, the drill points were not self-centering, which created position errors and holes oversized by as much as 0.003- 0.005” (0.08-0.13 mm). Because of this inaccuracy, Cashco had to drill holes undersize to a 0.005” tolerance and then bore the hole to meet the +0.002, -0.000” finish tolerance.

Connected to the accuracy problems were others involving productivity. The separate center drilling and boring operations slowed throughput. Cashco tried using carbide-tipped drills to allow faster feeds, only to break the carbide tools. "If we broke the drill, we scrapped the part," recalls Wallert. Because most of the holes in Cashco's parts are fairly deep, the deep boring operations also required slow feed to avoid tapering.

Still another factor in the search for a better way to make holes was a goal to increase machine utilization. "Our company uses a lot of CNC machines," notes Wallet, "and we couldn't justify using outdated drill points that prevented us from taking advantage of today's CNC technology and exotic materials."

By generating points today on a Winslow Engineering Model HC drill point grinder, Cashco not only has received ISO 9000 certification but also enjoys 5% higher productivity on machines that drive drills with Winslow-Helical and Winslow-Bickford points. Cashco drills directly to 0.002" (0.05-mm) tolerances, eliminating both the earlier separate center drilling and boring operations and the costs of scrap and tool breakage. The Winslow HC drill grinder paid for itself in one year.

"Our holemaking results were so predictable since we began using the Winslow-ground drill points that we have improved product quality ," says Wallert. "But that same uniformity has a positive impact on our people too.

Wallert recalls that he noticed the difference in Winslow-generated points immediately. "We knew right away that the Winslow-Helical point [see sidebar at right] was different from any other helical point we had seen," he says. "First of all, the Winslow-Helical point is self-centering. And because the Winslow-Helical point has more relief for clearance, it is freer cutting. This lets us use feed rates that are 25% higher than we could use to drive drills with conventional points."

Wallert says that spindle load meters keep showing how drills with the Winslow-Helical point carry only half the load of conventional-point drills. He says this holds true regardless of drill size or material.

How Conventional and Helical Points Differ

Because a conventionally ground drill point has a straight chisel edge with a large negative cutting angle, it pushes or extrudes the work material, rather than shearing it. The Winslow-Helical geometry has an S- shaped chisel edge with a small negative-rake cutting surface that starts cutting cleanly as it enters the work.

Still another difference Cashco recognized immediately upon changing to Winslow-Helical drill points was that the holes are straighter. This showed that drills with Winslow- Helical points do not flex or "walk."

Cashco grinds the Winslow-Bickford point geometry onto drills it uses for intersecting cross holes. "In addition to the advantages of a Winslow-Helical point, the Bickford point also minimizes burrs at break- through," says Wallert.

Why can some drills offer these advantages? Essentially, the answer lies in the geometry of the drill point and how the machine grinds the chisel edge on that point. The two basic methods are facet grinding and form grinding.

In conventional facet drill-point grinding, the grinding wheel and drill point make contact along one axis. The result is a drill point comprised of two large, relatively flat facets separated by a straight chisel edge that has a large negative cutting face. The large negative-rake cutting surface in front of this chisel can only push or extrude material, not actually cut it. On the other hand, triaxial grinding generates geometries of high-performance drill points, such as the Winslow-Helical and Winslow-Bickford points Cashco uses.

In triaxial drill point grinding, the grinding wheel and drill make contact through three axes of motion simultaneously to generate a variety of point geometries. Of these, the Winslow-Helical and Winslow- Bickford points include an S-shaped chisel edge with small negative angle. This provides the active cutting chisel a drill needs to cut chips instantly upon entering metal, makes such drills self-centering, and eliminates the need for a separate center- drilling operation.

The three axes of simultaneous triaxial motion on a Winslow Engineering drill grinding machine are a drill rotating about its axis to put the point on the drill's center, a vertical rise of the drill to form the chisel; and horizontal infeed to form the relief. Just as important as the triaxial grinding motion itself is the ability to make certain a point is ground on the center of each drill's axis of rotation. This is necessary to ensure balanced chip loads on each cutting lip-especially at the higher feed rates used today.

To grind points on center consistently, Winslow Engineering drill grinders grip each drill on the shank end with a collet and guide the fluted end with a bushing. The drill rotates about its axis during grinding-identical to the conditions that the drill has when making a hole. This accuracy determines the drill's performance and life.