This technical information has been contributed by
Tube Hollows International

What is Gundrilling?


Gundrilling is the process of drilling long or deep holes, first used in the making of gun barrels more than 100 years ago. Today's technology with refined machinery and tool design has made gundrilling a reliable high-production method for drilling short holes as well as deep holes.

History of Gundrilling

Gundrilling was first introduced in Europe more than two centuries ago. The process was born out of the need to generate the bore of gun barrels in a more efficient manner.

Originally, the most effective manner of manufacturing a gun barrel was to hand forge a long strip of steel around a rod (or mandrel) in a spiral fashion. This proved more a blacksmithing function than a manufacturing process. This method - a supreme credit to the craftsmen of the era - yielded many fine gun barrels (known as 'Damascus' barrels) which were highly prized and performed exceptionally well with the traditional 'black powder' of the time.

However, as the technology of firearm propellants evolved, the strength of the basic firearm was found to be wanting. Damascus barrels, which had performed well with black powder, tended to split wide open like a coil spring under the higher pressures of the new propellants.

An interim process consisted of drilling the bore of the barrel with a twist drill. This enabled the barrel to be fabricated from a solid - and thus stronger - bar of solid steel; but the method was slow and cumbersome, necessitating the need to retract the drill frequently to dispose of chips and apply more lubricant to the drill. Also, the depth of the hole necessitated using a set of drills - of identical diameter but with each successive tool having a greater length than the previous– such that the hole was actually step-drilled to full depth.

Enter gundrilling: this revolutionary method allowed the tool to drill the full length of the barrel without retraction by injecting cutting oil through the hollow shank. Once the oil had lubricated the cutting edges of the tip it escaped along the v-shaped flute of the shank, taking with it the chips.

As with any new process, gundrilling underwent constant development as related technologies evolved. The most significant improvements in the early stages were development of the high-pressure pump and the debut of sintered carbide. With the switch to carbide tips and high-pressure coolant, the process was able to yield faster cycle times and better finishes.

Improvement continued as experimentation showed that by varying tip geometries certain materials and conditions could be better accommodated. Concurrently, the modified engine lathes that were used from inception were gradually replaced with machines designed specifically for the gundrilling function. The first machines were built with high precision, but spindle drives and feed systems left a lot to be desired.

As time passed, development of the modern electric motor, more efficient high-pressure coolant systems, and stepping motors added the needed improvements. The later introduction of electronic speed controls and servomotors brought the design to its current state.

Gundrilling Today

The gundrill consists of a hollow tube with a "V" shaped groove or flute along its length, and a carbide cutting tip designed in such a way as to produce its own guide bushing as it drills the hole. High-pressure coolant is introduced into the center of the drill tube through the spindle of the gundrilling machine to help break and evacuate the chips along the "V" groove of the tool and out of the hole.

Gundrilling machines are built to an extreme degree of precision. Gundrilling provides very close tolerance straight holes with excellent surface finish, and is able to produce holes as small as .055". Digital positioning technology is used to maintain tolerances, true position, concentricity, and straightness of holes in prototypes and throughout production runs.

Today, 'conventional' gundrilling machines, X-Y knee machines for multiple hole drilling, and custom machines are available, all depending on your particular process requirements.

At this very moment, some form of the process is being utilized by every industry imaginable in a host of varied applications, not only in gundrilling machines, but as well in high-production special purpose machines, horizontal and vertical CNC machining centers, CNC turning centers, screw machines, and to complete the circle - the basic engine lathe.

Gundrilling Capabilities

Range of Materials

Types of Holes Possible

This technical information has been contributed by
Tube Hollows International

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