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Solutions for Challenging Deep Hole Drilling

UNISIG offers solutions to overcome four of the toughest deep holes to drill. These included jobs involving close hole concentricities from inner to outer diameters, extreme thin-wall diameter ratios, off-center and intersecting holes and holes with internal machining at depths that exceed a conventional boring bar's capabilities.

On-Center Holes, Close Concentricity and Telescoping Bores

"Many industries require parts with on-center drilling through difficult materials such as high-grade stainless steels, alloy steels, nickel alloys and titanium," said a company spokesperson. "These parts can run between 1 in. and 18 in. in diameter at depths in excess of 60 in. with concentricity from ID to OD held to within a few thousandths. A deep hole drilling machine from UNISIG that allows for counter rotation of drill and workpiece offers the ideal way to drill such parts at precise concentricities and optimum straightness."

In addition to drilling long, straight on-center holes, some parts require those same high-concentricity holes also have internal stepped or telescoping bores with varying sizes from one end of the workpiece to the other. On UNISIG's modern deep hole drilling machines, accuracy and process control make these tasks routine two- to three-minute cycles.

The aerospace industry, for example, often uses these close-tolerance, fine-finish bores on engine and landing gear components. In some instances, a telescoping bore-starting at its smaller diameter-would then be followed by a larger counterbore to two-thirds the final depth at close concentricity and finally by a hole that runs the rest of the part length no counterbore. "Such an operation is an easy task on UNISIG deep hole drilling equipment," said the spokesperson.

From Solid Material to Thin-Walled Tubing

"Purchased tubing and sleeves are sometimes unable to provide enough strength and stability for certain part specifications," said the spokesperson. "To produce a high-strength, thin-walled tubing-type part with no welds or seams, manufacturers often opt to drill out a piece of solid bar stock to produce the tubing. On a UNISIG deep hole drilling machine, the BTA process easily transforms solid stock into thin-walled tubing with high-integrity walls between 0.25 in. and 0.125 in. thick, eliminating the wait for special-ordered parts and improving quality and profitability in the process. Energy and aerospace components make ideal candidates for this process, as do parts for space exploration, defense and advanced scientific applications."

For these thin-walled tubing applications, today's BTA drilling capabilities incorporate servo clamping systems and workpiece compensation that tie directly in with machine controls and protect the thin walls generated during deep hole drilling from damage. The accuracy and precision of current deep hole drilling machines also helps eliminate deformities such as oval or oblong bores and buckled parts, especially in conjunction with thermal growth.

Drilling Small, Deep, Off-Center and Intersecting Holes

High-ratio holes dominate deep hole drilling, as do off-center ones. "Faced with producing a series of 30 in. deep 120:1 ratio holes on conventional equipment, many shops would give up on the task, failing to realize that even a simple UNISIG CNC gundrilling machine could position a workpiece and a tool to drill those types of holes with ease," said the spokesperson.

Such systems control the process with coolant delivery and force monitoring to produce straight results and promote long tool life. For close tolerances at greater depths, these deep hole drilling machines can perform simultaneous off-center indexing to further improve straightness and accuracy.

Besides those parts requiring off-center deep holes, others-such as feed tubes for plastic extrusion machines-add the complexity of intersecting dual off-center parallel holes that must remain perfectly drift-free and straight throughout their depths. To create them, the deep hole drilling machine fixture must push the workpiece off center and rotate it concentrically at high speeds to drill the hole on the machine's centerline while the workpiece spins on a different centerline.

"A turning center lacks the travel-and the specialized process control-to handle these types of jobs," said the spokesperson. "But a modern BTA process from UNISIG that burnishes while it bores, however, maintains the close concentricity of hole diameters so shops can drill an initial hole, slide in a ground plug, tack weld it in place and then bore another hole through both the material itself and the sacrificial plug."

Machining Inside a Bore

Called bottle boring or chamber boring, this process machines inside a bore-deeper than a conventional boring bar can reach-and cuts an accurate profile controlled via CNC contouring. For these types of part features, depths of cut can run deeper than the bores. These machining scenarios often involve aerospace parts, including helicopter rotor shafts, jet engine and landing gear components, as well as oil and gas, instrumentation, defense, space exploration and scientific and industrial applications.

"On conventional machine tools, this process requires highly specialized, costly form radius tools that require hours of work time but often fail to yield the necessary finish and diameter control," said the spokesperson. "UNISIG's advanced deep hole drilling equipment, on the other hand, can perform CNC turning operations on the inside of a hole by stabilizing the cut with the initial deep hole bore for extreme rigidity while machining. These specialized machines yield precise final geometries and finishes, working with a tuned bar, long extensions and no support to machine at depths of cut 0.5 in. to 1.0 in. deeper than the bore itself."

The spokesperson added, "When it comes to workpieces that require challenging deep hole drilling work, UNISIG can equip shops to tackle such difficult, specialized jobs effectively and productively-starting by helping its customers identify processes, tooling, workholding and accessories as well as supplying the best possible deep hole drilling system for the job. All backed by application and training support."

For more information contact:


N58W14630 Shawn Circle

Menomonee Falls, WI 53051


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