458 Modern Metalworking Copyright Goodheart-Willcox Co., Inc. 26.6.3 Rotary and Index Tables A manually operated rotary table, Figure 26-37, is 7 7 a workholding attachment that consists of a circular worktable rotated by a handwheel through a worm and worm gear. The hub of the handwheel is gradu- ated in degrees, permitting the precise spacing of the cuts (holes, slots, grooves, etc.) around the piece. The rotary table is used to perform a variety of operations, including cutting segments of circles, circular slots, and irregular slots, as well as locating angular-spaced holes or slots. A dividing attachment can be fitted in place of the handwheel. Not all rotary tables are manually operated. Some are integrated into CNC milling machines and machine tools. Automated worm gear-driven rotary tables are operated by stepper or servo motors. They are often used to achieve fourth- and fifth-axis movement for CNC machining, Figure 26-38. An index table, Figure 26-39, is a workholding attachment that permits the rapid positioning of the material for angular work. Most index tables have increments of 15°. 26.6.4 Dividing Head The main function of a dividing head is to divide the circumference of a circular piece into equally spaced divisions. This makes the dividing head indispens- able when milling gear teeth, cutting splines, and spacing holes on a circle. It also makes possible the milling of shapes such as squares, hexagons, and octagons. The dividing head consists of two parts: a divid- ing unit and a foot stock. The work may be mounted between centers, held in a chuck, or clamped in a collet, Figure 26-40. An index plate, identified by circles of holes on its face, and the index crank, which revolves on the index k plate, are fundamental in the dividing operation. Rotating the index crank causes the dividing head spindle (to which the work is mounted) to rotate. The standard ratio for a dividing head is five turns of the index crank for one complete revolution of the spindle (5:1) or 40 turns of the index crank for one revolution of the spindle (40:1). The ratio between the index crank turns and spindle revolution, plus the index plate with its series of equally spaced hole circles, makes it possible to divide the circumference of circular work into the Dmitry KalinovskyShutterstock.com Figure 26-38. This tilting rotary table can be installed on machining centers. Yukiwa Seiko USA, Inc. Figure 26-39. An index table permits work to be rapidly positioned at different angles. The unit can be mounted vertically or horizontally. WMW Machinery, Inc. Figure 26-37. A rotary table can used to precisely space cuts, such as holes, slots, and grooves, around a workpiece.