Single Flute Gundrills
Gundrills are carbide tipped, steel shank drills, known for producing long, straight, close tolerance holes, at a high penetration rate, and with a superior surface finish. These “deep hole drills” are generally employed when the hole exceeds 5-6 diameters in depth, and offer size location and straightness accuracy where critical tolerances are important. It’s an economical operation, often eliminating one or more secondary operations. Gundrilling offers the capability of burr-free holes and bottom forming of blind holes, as well as entry into surfaces at angles other than 90 degrees.
Hyper Tool produces Gundrills in diameters from .063 thru 2”, and in lengths exceeding 8-10 feet. Hyper’s Threadlock Detachable Head Gundrills are available up to 3” in diameter. Materials commonly gundrilled include cast iron, carbon and alloy steel, tool steel, high temperature alloys, titanium, beryllium, copper, brass, and aluminum, as well as graphite, wood, plastic and fiberglass. They require a high-pressure coolant to be injected at the back end, which then lubricates the cutting edge and exhausts the chips down the straight flute. They also require either a starting bushing or a pre-drilled starter hole, as they are self-piloting once in the hole, but not self-centering at the start.
Initially gundrilling applications were limited to concentric parts, such as gun barrels, as the part had to spin while the drill was held stationary. Gundrilling grew in popularity once it was learned how to inject the coolant into a spinning drill, thus allowing any shaped part to be gundrilled. Special gundrill machines were required to accommodate both the coolant injection and the starting bushing.
The latest growth spurt in the industry has come with the introduction of CNC Machining Centers and Lathes, which flow coolant through the spindle, and are able to pre-drill accurate starter holes as part of an automatic operation. This has opened up a whole new market of potential gundrill users. Today gundrilling is widely used for short run job shop work as well as for high production runs.
Gundrills come in both single-flute and two-flute configurations. Two-flute gundrills can cost 2 to 3 times as much as single flute gundrills, but they have been the tool of choice for people drilling both aluminum and cast iron, as they typically can be run at twice the penetration rate of single flutes.
We believe we have rendered the two-flute gundrill largely obsolete, as a result of the research and product development we have conducted. The single flute drill we developed for an automotive company, for example, penetrates their aluminum engine blocks at double the traditional rate of a two-flute gundrill. Similarly, we have replaced two-flute gundrills at a major truck engine manufacturer, drilling cast iron engine blocks, with no reduction in their penetration rate, but with a straighter hole and at half the cost.
Today Gundrilling applications
span a wide variety of industries, including the Automotive (engine
parts, valves, fuel injectors, brakes, etc), Aerospace, Medical, Plastic
Injection Mold, Farm Equipment, Firearms, Pumps, Refrigeration, Paper,
Food Mixing, and General Manufacturing.
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