The jig borer is a type of machine tool invented at the end of World War I to enable the quick and precise location of hole centers. It was invented independently in Switzerland and the United States.[1] It resembles a specialized kind of milling machine that provides tool and die makers with a higher degree of positioning precision (repeatability) and accuracy than those provided by general machines. Although capable of light milling, a jig borer is more suited to highly accurate drilling, boring, and reaming, where the quill or headstock does not see the significant side loading that it would with mill work. The result is a machine designed more for location accuracy than heavy material removal.
A typical jig borer has a work table of around 400 by 200 millimetres (15.7 in × 7.9 in) 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 allows positions to be set on the two axes to an accuracy of 0.0001 inches (2.5 μm). It is generally used to enlarge to a precise size smaller holes drilled with less accurate machinery in approximately the correct place (that is, with the small hole strictly within the area to be bored out for the large hole).
Jig borers are limited to working materials that are still soft enough to be bored. Often a jig is hardened; for a jig borer this requires the material to be bored first and then hardened, which may introduce distortion. Consequently, the jig grinder was developed as a machine with the precision of the jig borer, but capable of working materials in their hardened state.[2]
- ^ Moltrecht, Karl Hans: Machine Shop Practice, 2nd ed. New York: Industrial Press, 1981, Volume 1, p. 403.
- ^ Moore (1970), p. 162.