Machine Tools

Boring machines are similar in construction to milling machines except they are generally more massive and built lower to the floor, use different tooling, and feed differently along the axis of the spindle. Boring machines are typically located in very clean, climate controlled environments and are massive for extra rigidity and vibration damping to ensure close tolerance hole sizes and locations, one example being automobile engine piston bores.

Jig boring machines are primarily intended for tool-room use and are used to produce precision dies, jigs, and gages, which are used to ensure the accuracy and interchangeability of high volume production parts. There are three common designs of jig boring machines in use, the open-sided or C-frame, adjustable-rail, and fixed-bridge construction. Variations of the jig boring machine include jig grinders, which are used to realign holes after hardening, and the horizontal jig boring and milling machine, which is utilized for general production operations.

The base of the jig boring machine supports a saddle that moves in and out from the operator to the column. A table moves right or left on the saddle to complement the saddle movement. A massive column supports the spindle housing, which adjusts to the work location by moving up and down the column ways. The spindle moves inside a quill that is supported by the housing or spindlehead.

The quill also moves up and down inside the housing to give a telescoping mechanism which adds rigidity to the spindle. The spindle, quill, and housing are manufactured under very careful and exacting conditions to eliminate any lost motion. The housing is usually made of Invar cast iron to minimize errors due to thermal expansion. Stability of the housing is extremely critical because any expansion would change the tool location relative to the column.

The spindle is hardened, ground, and lapped. Preloaded ball bearings also help to eliminate lost motion of the tool and its driving mechanism. Spindle speeds range from 30-1,500 rpm on an average machine. A digital readout (DRO) system is used to provide a continuous numerical readout of the table position. Jig boring machines may also be computer numerically controlled (CNC). CNC control permits many additional jobs that would be impossible with a manually operated machine. One example would be to produce precise, irregularly curved forms to be generated on cams or master templates without operator involvement.