The jig borer is a type of machine tool invented at the end of World War I to make possible the quick-yet-very-precise location of hole centers. It was invented independently in Switzerland and the United States.^[1] It can be viewed as a specialized species of milling machine that provided tool and die makers with a higher degree of positioning precision (repeatability) and accuracy than those general machines had previously provided.

A typical jig borer had a work table of around 400 x 200 mm, which can be moved using large handwheels (with micrometer-style readouts and verniers) on particularly carefully made shafts with a strong degree of gearing; this allowed positions to be set on the two axes to an accuracy of 0.0001 inch (2.5 micrometres). It was generally used to enlarge to a precise size smaller holes drilled with less accurate machinery in approximately the correct place (IE with the small hole strictly within the area to be bored out for the large hole).

History[link]

Before the jig borer was developed, hole center location had been accomplished either with layout (either quickly-but-imprecisely or painstakingly-and-precisely) or with drill jigs (themselves made with painstaking-and-precise layout). The jig borer was invented to expedite the making of drill jigs, but it helped to eliminate the need for drill jigs entirely by making quick precision directly available for the parts that the jigs would have been created for. The revolutionary underlying principle was that advances in machine tool control that expedited the making of jigs were fundamentally a way to expedite the cutting process itself, for which the jig was just a means to an end. Thus the jig borer's development helped advance machine tool technology toward later NC and CNC development. The jig borer was a logical extension of manual machine tool technology that began to incorporate some then-novel concepts that would become routine with NC and CNC control, such as:

• coordinate dimensioning (dimensioning of all locations on the part from a single reference point);
• working routinely in "tenths" (ten-thousandths of an inch, 0.0001 inch) as a fast, everyday machine capability (whereas it formerly was the exclusive domain of special, time-consuming, craftsman-dependent manual skills); and
• circumventing jigs altogether.

Franklin D. Jones, in his textbook Machine Shop Training Course (5th ed),^[2] noted:

"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."

The technological advances that led to the jig borer and NC were about to usher in the age of CNC and CAD/CAM, radically changing the way humans manufactured many of their goods. The potential of control technology that would gradually eliminate many needs for jigs—and also often eliminate the need for the jobs of the operators who used them—was little appreciated outside of a few R&D laboratories when Jones recorded his observation.

References[link]

Dancing the Haymakers' Jig at an Irish ceili

The Jig (Irish: port) is a form of lively folk dance in compound meter, as well as the accompanying dance tune. It developed in 16th century England, and was quickly adopted on the Continent where it eventually became the final movement of the mature Baroque dance suite (the French gigue; Italian and Spanish giga).^[1] Today it is most associated with Irish dance music and Scottish country dance music.^[2] Jigs were originally in duple compound meter, (e.g., 12/8 time), but have been adapted to a variety of time signatures, by which they are often classified into groups, including light jigs, slip jigs, single jigs, double jigs, and treble jigs.

Origins[link]

English Elizabethan clown Will Kempe dancing a jig from Norwich to London in 1600

The term jig was probably derived from the French giguer, meaning 'to jump' or the Italian giga.^[3] It was known as a dance in sixteenth-century England, often in 12/8 time, and the term was used for a dancing entertainment in 16th-century plays.^[4] Later the dance began to be associated with music particularly in 6/8 time, and with slip jigs 9/8 time.^[5]

Ireland and Scotland[link]

During the seventeenth century the dance was adopted in Ireland and Scotland, where it was widely adapted, and the jig is now most often associated with these countries.^[6] The jig is second in popularity only to the reel in traditional Irish dance; it is popular but somewhat less common in Scottish country dance music. It is transcribed in compound meter, being 6/8 time. The most common structure of a jig is two eight-bar parts, performing two different steps, each once on the right foot, and one on the left foot. As with most other types of dance tunes in Irish music, at a session or a dance it is common for two or more jigs to be strung together in a set, flowing on without interruption.

Light jigs[link]

Feet shod in Irish dance hard shoes

A light jig is the fastest of all the jigs, danced in ghillies, and are performed in 6/8 time. The performer's feet rarely leave the ground for long, as the step is fast, typically performed at a speed around 116 at feiseanna. There are several light jig steps, varying with each dance school, but one step is almost standard in all light jigs. This step is known as the rising step, or the rise and grind. This is the right side version of it: Put your weight on your left foot and lift your right foot off the ground. Hop on your left foot once. Hop on your left foot again, bringing your right foot back behind your left foot and then shift your weight onto your right foot, leaving your left foot in the air. Dancers use the phrase "hop, hop back" for these three movements, and there is a slight pause between the hop, and hop back. The next movement is a hop on your right foot. Then you shift your weight on your feet , left-right-left-right. The phrase for this whole movement is: "hop, hop back, hop back 2-3-4." To do the step on the left foot, reverse the left and right directions.^[7]

Slip jigs[link]

Slip jigs are in 9/8 time. Because of the longer measures, they are longer than the reel and the light jig, with the same number of bars to the music.^[8] The dance is performed high on the toes, and is often considered the "ballet of Irish dance" because of its graceful movements that seem to slip the performers across the floor. Slip jigs are performed at a speed of 112 at feiseanna.

Single jigs[link]

Single Jigs should not be confused with slides; they are the least common of the jigs, performed in ghillies, in a 6/8 or less commonly a 12/8 time. Musically, the Single Jig tends to follow the pattern of a quarter note followed by an eighth note (twice per 6/8 bar), whereas the Double Jig follows the pattern of having three eighth notes (twice per 6/8 bar).

Hop jigs[link]

The term Hop Jig is the subject of some confusion, as some people use it for a single jig,^[9] while others use this term to refer to a tune in 9/8 time (e.g., Francis O'Neill^[10]). Among the latter, some do not distinguish it from a slip jig, while some reserve the term to a slip-jig variant that has special characteristics, in particular an emphasis on 1/4 - 1/8 pairs.^[9]

Treble jigs[link]

	The Old Grey Goose A jig featuring the tin whistle, performed by Dancing Willow
Problems listening to this file? See media help.

Treble jigs (also called the Hard or Heavy jig) are performed in hard shoes, and also to a 6/8 time meter. They are characterized by stomps, trebles, and clicks. Many set dances are performed in treble jig time, a few being Drunken Gauger, Blackthorn Stick, The Three Sea Captains, and St Patrick's Day. Two types of treble jigs are performed at feiseanna: the traditional and non-traditional (slow) treble jigs. Beginners will do a treble jig at traditional speed (92 bpm), while more advanced dancers will dance the non-traditional (slow) treble jig at 72 bpm.

See also[link]

• Gigue
• Hornpipe
• Irish stepdance
• Mazurka
• Polka
• Reel
• Slide
• Slip jig
• Highland Fling
• Schottische
• Strathspey (dance)
• Waltz

Notes[link]

Bibliography[link]

• Baskerville, Charles Read. The Elizabethan Jig. 1929.
• Brissenden, Alan. Shakespeare and the Dance. 1981.

External links[link]

• Irish footwork