What Is Jig Boring Machine?- Types and Working

What is Jig Boring Machine?

The jig borer emerged around the end of World War I, developed both in Switzerland and the United States, as a response to the need for swift and extremely precise location of hole centers.

At first glance, this machine resembles a specialized form of milling machine, but it was designed specifically to offer tool and die makers a much higher level of positional accuracy and repeatability than what standard equipment could provide.

While a jig borer is capable of some light milling, its real strength lies in tasks that demand precision, such as accurate drilling, boring, and reaming. Unlike conventional milling machines, the jig borer’s quill or headstock is not subjected to significant side forces, as it isn’t intended for heavy-duty material removal. In essence, the design prioritizes positional accuracy over sheer cutting power.

Typically, you’ll find a jig borer equipped with a work table measuring roughly 400 by 200 mm (or about 16 by 8 inches). Operators adjust the table using large handwheels that are fitted with micrometer-style readouts and vernier scales, all built with impressive care and robust gearing.

This arrangement allows users to position workpieces with remarkable precision, down to 0.0001 inches, or 2.5 microns, on both axes.

In practical use, the jig borer often comes into play after an initial hole has been drilled by less precise equipment. The operator will enlarge these roughly located holes to their final, exact dimensions, ensuring that the small pilot hole stays within the boundary to be bored for the larger, finished hole.

One limitation worth noting: jig borers are only effective on materials soft enough to be bored. Since jigs are frequently hardened for durability, this typically means boring must occur before the hardening process—though this introduces the risk of distortion.

To address this issue, the jig grinder was later developed, offering the same level of accuracy as the jig borer but with the added ability to machine hardened materials.

History

Before the advent of the jig borer, machinists had two main options for locating hole centers: they could lay them out by hand—which was either quick but imprecise, or extremely painstaking if precision was the goal—or they could use drill jigs. Ironically, those drill jigs themselves required the same painstaking layout to be made accurately in the first place.

The invention of the jig borer initially aimed to speed up the production of drill jigs. However, its impact went further: it made high-precision hole placement directly accessible, often making the use of jigs unnecessary for the very parts they were intended to help manufacture.

The underlying shift here was more than just a matter of convenience. Improvements in machine tool control that sped up jig making essentially pointed to a deeper idea: that the real breakthrough lay in expediting the cutting process itself, with jigs merely serving as an intermediary step. By sidestepping that extra step, the jig borer moved manufacturing forward in a fundamental way.

With its introduction, the jig borer marked a step toward technologies like numerical control (NC) and computer numerical control (CNC). It brought into manual machining some forward-thinking practices that would later become standard with NC and CNC, such as:

• Using coordinate dimensioning—measuring all locations on a part from a single, consistent reference point.
• Treating accuracy to the “tenths” (that is, to 0.0001 inch) as a routine matter, not just a slow, specialist skill.
• And, perhaps most significantly, eliminating the need for jigs entirely in many cases.

Franklin D. Jones put it neatly in his textbook Machine Shop Training Course (5th ed.):
“In many cases, a jig borer is a ‘jig eliminator.’ In other words, such a machine may be used instead of a jig either when the quantity of work is not large enough to warrant making a jig or when there is insufficient time for jig making.”

A number of the innovations behind the jig borer can be traced back to the Moore Special Tool Company. Notably, they introduced hardened and precisely ground leadscrews, a step up from the older approach of using a soft leadscrew with a compensating nut.

All of these advances paved the way for NC, and soon after, CNC and CAD/CAM systems—technologies that have profoundly changed how products are manufactured across industries.

Types of Jig Boring Machine

There are mainly two types of jig boring machines:

• Vertical milling machine type
• Planer Type

1. Vertical Milling Machine Type

In terms of construction, this type of machine resembles a vertical milling machine. The spindle is mounted on a vertical column, while the horizontal table is positioned on the bed directly in front of the column.

The workpiece is secured on the table, and its position can be adjusted through combined movements of the table—both perpendicular and parallel to the column face.

2. Planer Type

The structure consists of two vertical columns positioned on either side of the table, both securely mounted to the base. The table itself moves back and forth to allow precise adjustments of the workpiece. Meanwhile, the spindle is mounted on the cross rail, which connects the two vertical columns.

In the case of a planer-type jig borer, locating holes involves two coordinated movements. The table moves lengthwise, while the spindle can travel laterally across the cross rail. Together, these movements make it possible to achieve accurate positioning for drilling operations.

Applications of Jig boring Machine

Following are the applications of jig boring machine:

• The jig borer is used for the pilot hole.
• It is used to make compound and progressive dies.
• It is also used for drilling holes in jig-bushing.
• Jig borer is commonly used for jigs, fixtures and dies & bushing hole for grinding & A grinding the hardened parts.
• Also used in alignment post in stripper or die set

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