What is a Jig Boring Machine?
The jig borer stands out as a highly specialized machine tool designed primarily for achieving precise hole location and enlargement in metal and plastic components. Invented at the conclusion of World War I, it was developed independently in Switzerland and the United States to enhance the speed and accuracy of hole positioning. Resembling a refined form of milling machine, the jig borer offers superior repeatability and positional accuracy, making it an indispensable tool for tool and die makers.
While capable of light milling operations, its core strength lies in highly accurate drilling, boring, and reaming tasks. The machine’s design minimizes lateral forces on the spindle, ensuring maximum precision during operation. Typically, a jig borer features a work table measuring approximately 400 x 200 mm (16 x 8 inches), which can be moved with large, finely graduated handwheels that incorporate micrometer-style readouts and vernier scales. This setup allows operators to position tools with an accuracy of up to 0.0001 inches (2.5 microns).
The primary application of a jig borer is to enlarge smaller pre-drilled holes to precise dimensions, especially when initial manual or less accurate drilling methods are employed. Its capability to work on softer materials allows for the creation of hardened jigs and fixtures, although the process involves first drilling and then hardening these components, which can sometimes introduce distortions. To overcome this, the development of jig grinders emerged, capable of working on hardened materials with the same high precision as jig borers.
Historical Background
Before the advent of jig borers, locating hole centers depended on manual layout techniques—either rapid but imprecise or painstaking and highly accurate—or on drill jigs crafted through detailed layout work. The invention of the jig borer revolutionized this process by enabling direct, rapid, and precise hole placement, effectively reducing or eliminating the need for dedicated jigs.
The core principle behind the jig borer was that advancements in machine control technology could expedite the manufacturing process itself. The machine’s capability to produce intricate and accurate holes directly on workpieces paved the way for later developments such as Numerical Control (NC) and Computer Numerical Control (CNC). This innovation marked a significant step toward modern automation in manufacturing.
According to Franklin D. Jones in his authoritative textbook, Machine Shop Training Course, the jig borer can often serve as a “jig eliminator,” especially when production runs are too small to justify making jigs or when time constraints prevent traditional jig creation. This underscores the machine’s efficiency and versatility in modern manufacturing environments.
Several key innovations, notably from the Moore Special Tool Company, contributed to the development of the jig borer. These included the adoption of hardened and accurately ground leadscrews, replacing earlier designs that used softer screws with compensating nuts. Such technological improvements significantly enhanced the machine’s precision and durability, setting the stage for the subsequent rise of NC and CNC automation systems, which transformed manufacturing in the 20th century.
Types of Jig Boring Machines
Jig borers are generally categorized into two main types based on their construction and operational principle:
- Vertical Milling Machine Type: This configuration resembles a vertical milling machine, with a rotating spindle mounted on a vertical column. The workpiece rests on a horizontal table that can be moved precisely in multiple directions through handwheels equipped with micrometer adjustments. This setup allows for accurate positioning of the workpiece relative to the spindle.
- Planer Type: Featuring two vertical columns flanking a large work table, this design employs a reciprocating table that moves longitudinally. The spindle is mounted on a cross rail bridging the two columns, enabling coordinated movement along two axes for precise hole location and enlargement. This configuration is ideal for handling larger workpieces requiring high accuracy.
Vertical Milling Machine Type
This type operates similarly to a standard vertical milling machine, where the spindle rotates on a vertical axis, and the workpiece is secured on a movable table. The table can be adjusted using precise handwheels to position the work in relation to the spindle, facilitating accurate hole placement through combined movements.
Planer Type
In this design, the machine features two vertical guiding columns with a fixed cross rail supporting the spindle. The worktable reciprocates along the length of the machine, while the spindle moves transversely. This configuration allows for high-precision hole drilling over larger workpieces with complex geometries.
Applications of Jig Boring Machines
The versatility of jig borers makes them suitable for various specialized manufacturing tasks, including:
- Creating precise pilot holes in metal and plastic components.
- Fabricating complex and progressive dies used in mass production.
- Drilling accurately positioned holes in jig bushings and fixtures.
- Manufacturing jigs, fixtures, and dies, especially when working with hardened parts requiring grinding and finishing.
- Aligning posts within stripper or die sets to ensure accurate assembly and operation.
Frequently Asked Questions (FAQs)
What is a jig boring machine used for?
A jig boring machine is primarily used for creating highly accurate holes in workpieces, with the capability to position tools with micron-level precision. Its repeatability allows identical holes to be produced consistently, which is vital for manufacturing jigs, fixtures, and high-precision components.
How precise is a jig boring machine?
Jig borers are renowned for their exceptional accuracy, often achieving tolerances as tight as 2 micrometers (0.0001 inches). Typically, they operate within a range of 5 to 10 micrometers (0.0002 to 0.0004 inches), making them indispensable for applications requiring strict dimensional control.
What is a boring machine used for?
A boring machine is employed to enlarge existing holes with high precision and smoothness. It can accommodate various cutting tools such as steel, cemented carbide, or diamond-tipped bits, and is essential for producing accurate, smooth boreholes in various materials.
What is a jig milling machine?
Jig milling machines are automated milling systems categorized as plunger jigs, diaphragm jigs, air-pulsating jigs, and moving jigs. Among these, plunger jigs are obsolete. These machines are used for high-precision milling operations, often in conjunction with jigs and fixtures for complex machining tasks.
Are jig borers obsolete?
Yes, traditional jig borers have largely become obsolete with the advent of CNC machining centers. However, jig grinders remain vital for specific high-precision grinding applications, maintaining their relevance in specialized manufacturing sectors.
Why is it called a jig borer?
The term “jig borer” derives from its primary function—boring holes with extraordinary accuracy at precise locations. It was originally designed to create the essential components for jigs and fixtures, which are used to guide other machining operations. The machine’s ability to produce highly accurate holes directly on workpieces is the reason for its name.