Gundrilling Info

Single Flute Gundrills

Single Flute Gundrills consist of a carbide tip, a heat treated alloy shank, and a steel driver, typically silver brazed together into one precision unit.

Tip: The most critical element, the tip cuts the hole as it pilots the drill through the work piece, producing precision holes in a single pass. The drill’s point, or nose grind, has two basic angles that may be varied for optimum results depending upon the material being drilled. These angles balance cutting forces, distributing them to the tip’s bearing pads to keep the drill concentric. The tip is slightly larger than the shank, so the shank can rotate freely without contacting the hole wall. A round, kidney-shaped, or two round holes through the tip line up with the shank’s channel to allow the flow of coolant at high pressures.

Shank: The shank is made from aircraft grade alloy steel tubing with a110° -120° Vee-flute formed to the center of the shank’s diameter. Coolant is forced from the driver through the center of the shank to the tip, where it is flushed back along the shank’s flute. The shank maintains proper gundrill alignment and must be strong enough to absorb cutting torque and thrust. If the shank is too stiff it may transfer minor mis-alignment in the machine to the tip, but it must not be flexible enough to sag or whip at high RPMs.

Driver: Drivers are cylindrical, with an undercut or flat section for the set screw, which holds in the spindle bore. They are manufactured to industry standards or to special diameters and a concentric hole through the driver’s length allow coolant to pass through to the shank and tip.

Solid Carbide Single Flute Gundrills

Solid Carbide Single Flute Gundrills are manufactured as a single piece of carbide, replacing the tip and tubes braze section resulting in an extremely strong, ridged tool. Most small diameter drills significantly benefit from solid carbide drills because they yield the maximum allowable surface footage and feed rates with decreased whip factor do the their rigidity. Our solid carbide drills are manufactured through a new process using modern CNC equipment resulting in high quality and faster lead times. Long lead times are a thing of the past.

Two Flute Gundrills

Two Flute Gundrills are used in non-ferrous materials and allow for up to 80% increase in feed rates. Special nose configurations are designed and must be exactly duplicated to obtain repeatability. When using this type of drill the increased feed rates require more coolant pressure to evacuate the chips. The rule of thumb is 20% – 30% more than the required single flute specifications.

Step and Pilot Drills

Step and Pilot drills may be combined in one application to eliminate two to three subsequent operations in a single hole. The use of a step tool dramatically reduces cycle time, scrap, and eccentricity between diameters. Step drills have manufacturing limitations depending on extreme diameter ranges in the steps. Special carbide developing may sometimes be necessary do to the coolant hole location. Additionally chip breakers may be required do to the lack of an inside angle which curls and breaks the chips under normal circumstances. Ideally using this type of drill yields virtually no eccentricity between diameters. Non-cutting pilot drills are used to follow an existing hole while cutting a larger diameter and reducing cycle times plus minimizing eccentricity between holes.

Interlocking Detachable Heads

Interlocking detachable heads allow you to install a new head in minutes without removing the shaft from the assembly. Benefits include no down time, increased tool life and greater productivity. Order them to fit your existing drivers, shanks, and detachable heads. If your standard shanks are in good condition, you can convert to this system.

Eldo-Loc® Detachable Tip

Eldo-Loc® Detachable Tip construction provides easier handling of extra long or large diameter gundrills. This is an optional method available for gundrills from .625″ (15.875mm) to 2.375″ (60.325mm) diameter.

Gundrill Machines

Gundrill Machines are designed to provide optimum conditions for gundrill operation; the gundrilling machine’s high pressure pump delivers lubricant to the rear of the drill. The drill can be driven by the spindle or be held stationary if the work piece is rotated. During drilling, the work piece can be advanced or the drill can advance. The gundrill is supported by anti-whip devices along the shank and at the rear of the chip box. The chip box contains chip deflectors and a front end bushing, which guides the drill into the work piece. The chip box also contains escaping chips and lubricant, which are separated and filtered.

Gundrilling on CNC Machining Centers, Mills, Screw Machines, Lathes

or virtually any machine with through the spindle high pressure coolant capabilities can adapt the gundrilling process. The tool selection and operation sequence is the same as the conventional gundrill machine with the exception that a pilot hole is needed to replace the starter bushing. The general rule of thumb is one to two times diameter in depth and .0005″ larger in diameter. It is preferred that a flat bottom form is produced to eliminate the chance of deflection at the point of entry. If this cannot be obtained the pilot angle must match the outside angle of the gundrill. The truer the pilot hole, the straighter the hole. When possible, the tool should approach the pilot hole rotating backwards at about 25 RPM to compensate for any misalignment between the spindle, tool holder, or tool alignment. Once inside the pilot hole the tool will stop at about .100″ from the bottom and the coolant is turned on and RPM is started. The tool will now drill at the predetermined feeds and speeds (without pecking). At the bottom of the hole “either blind or through” the tool is immediately retracted (no dwell) to the original starting position. The coolant and RPM is shut-off and the tool may be retracted fully out of the part.