A qualified approach to machining complex, deep holes

Courtesy of All images: Sandvik Coromant

This special, based on a Sandvik Coromant Type-424.10 T-Max drill, is part of a single-tube application system for deep-hole machining.

Learn more about deep-hole machining

For more information on deep-hole machining, view a video presentation here.

Very deep, complex holes are becoming increasingly challenging to machine as hole tolerances become tighter and surface finish requirements get finer. In addition, components often require unique features, such as chambers, profiles, grooves, threads and hole-diameter and hole-direction variations. Efficiently machining these types of part features with tighter tolerances requires experience, R&D resources, engineering capability, application facilities and meaningful cooperation between a shop and its cutting tool supplier.

Machining holes from 10 to hundreds of diameters deep is an area dominated by application-specific tools. Deep-hole machining takes place in several industries, but is more common in machining energy and aerospace components because they typically require many deep holes, such as in landing gears, oil exploration components and turbine axles.

Some deep-hole features seem impossible to generate, but special tools can simplify operations, ensure high productivity and provide a strong degree of machining security.

The development of modern deep-hole machining (DHM) technology came about because of a growing need for complex holes and the unacceptably long machining times that resulted. Deep-hole drilling with cemented carbide tools has been an efficient method for several decades, but machining down-hole features has become a bottleneck.

DHM success is usually achieved by applying a mix of standard and special tools. This base knowledge, combined with design and field experience, leads users toward tools engineered for DHM. For example, precision tools with expandable toolholders help meet the challenges of chamber boring. Integrated support functions for the tool and reamer capability are combined with the latest carbide grades as well as efficient coolant and chip management. Support functions range from simple support pads to complex, fold-out supports on DHM tools.

Size Matters

When deep-hole drilling, holes below 0.040 ” in diameter can be made with gundrills, while intermediate holes (from 0.040 ” to 0.590 “) can be made with gundrills, ground carbide-tipped drills and exchangeable-tip carbide drills, depending upon hole depth. For 0.591 “-dia. and larger holes, brazed-carbide drilling heads are more efficient. For even larger hole diameters—0.984 ” and above—indexable-insert drills are preferred. Modern indexable-insert technology and drill-tube systems have led to the development of engineered DHM tools.

When deep-hole machining holes below 0.040 ” in diameter, a carbide gundrill is effective, while intermediate holes (from 0.040 ” to 0.590 “) can be made with a variety of tools. For holes 0.591 ” in diameter and larger, a brazed-carbide drilling head can be applied. Single-tube or ejector twin-tube DHM systems (top) using indexable-insert heads (above) are effective for drilling holes 0.984 ” in diameter and larger.

Holes with depths hundreds of times their diameters require specialized single- or double-tube gundrilling systems. Machining a long way into and at the ends of these types of holes requires qualified-movement mechanisms, new tool configurations and the proper cutting edges to make and finish chambers, grooves, threads and cavities.

When machining deep-hole features, users must consider in-process tool stability. Therefore, support pad technology is an important factor.

Process Opportunities

Today’s complex components and machining productivity demands require DHM solutions as opposed to deep-hole drilling followed by single-edge boring-bar operations, often performed on separate machine tools. Advanced DHM tools, combined with multitask machines, can complete deep-hole operations in one setup. This broadens machining capabilities, making it possible to machine demanding features more efficiently, while achieving tighter tolerances.