Selecting the appropriate drill design

If asked to name common machining operations, machinists and toolmakers likely would reply with varied lists based on experiences. Although varied, all lists probably would include drilling.

Drilling is a manufacturing process that has been used for millennia. Its roots can be traced to ancient Egypt when pyramid builders drilled holes in rock to construct the massive structures. Early methods were crude by today’s standards. But as the world became more industrialized, advances in workpiece materials and the need for greater accuracy demanded improvements in drilling technology.

In some manufacturing facilities, like those where machining occurs, drilling is an integral part of product realization. In other types of manufacturing, like food production, drilling is not integral to production but is certainly required for machinery and facilities maintenance. Therefore, it is safe to say holemaking is a critical process in all types of modern manufacturing.

Replaceable carbide tips are molded so they conform to the shape of the drill body. Image courtesy of C. Tate

Drilling as most people know it dates to Stephen Morse’s invention of the twist drill, which was patented in 1863. Although drills had been manufactured for centuries, his twist drill design is the most familiar and the basis for many modern drilling tools. This was a major change. Now, a person could drill vertically and still evacuate chips without re-cutting them.

The twist drill is easily recognized by the distinctive helical flutes, or grooves, that run most of its length. Helical flutes pull chips from the hole and allow cutting fluids to access the work zone. The name originated from the manufacturing process developed by Morse whereby the round drill blanks were twisted after the flutes had been milled.

Modern twist drills are usually made from HSS, but cobalt-alloy, solid-carbide and carbide-tipped twist drills are common. Twist drills are available in countless sizes, lengths, shank types and point angles depending on whether the workpiece material generates long or short chips. This variety makes the twist drill the go-to drill in most circumstances.

Index or Replace

Indexable carbide inserts dramatically changed cutting tools in the mid-20th century by ushering in new tool designs and boosting efficiency in all types of machining operations, including drilling.

Indexable carbide-insert drills have become common cutting tools, as they offer several advantages. Indexable drills have penetration rates that are four to five times greater than HSS drills, resulting in faster cycle times. Carbide inserts also extend tool life compared with HSS tools, especially when cutting difficult-to-machine materials.

Indexable carbide inserts offer long life, high performance and easy edge renewal. Image courtesy of C. Tate