CNC TURNING AND BORING Machinery's Handbook, 31st Edition
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b
W
A
b
a
P
a
P
B
W
B
A
R
R
B = (90 - A) / 2 B = A / 2 W = R x tanB a = W x sinA b = W x cosA Fig. 27. Calculation of Tangent Points.
Turning and Boring.— With the advancement of computer technology, control manu facturers have developed cutting cycles capable of complex lathe operations and made them an integral part of the lathe control systems. These special cycles are called Multiple Repetitive Cycles . Their main attraction is their excellent flexibility. Some of these ad - vanced cycles cover turning and boring, others grooving and threading. These cycles are only complex in the mathematical sense and even then, only within the control system. In practice, these advanced machining cycles are easy to program. Their other benefit is that they can be easily changed at the control terminal to be optimized for best performance. The most common multiple repetitive cycles are: Table 6. Multiple Repetitive Cycles G-Code Description G-Code Description G70 Contour finishing cycle (used after G71, G72, and G73) G74 Peck drilling cycle—along the Z-axis G71 Roughing cycle—horizontal direction G75 Peck grooving cycle—along the X-axis G72 Roughing cycle—vertical direction G76 Single point threading cycle (straight or tapered) G73 Pattern repeating roughing cycle For turning and boring operations, G71 cycle is the most common, along with G76 cycle for threading (described separately). Roughing Cycle (G71): The most common roughing cycle is G71. Its purpose is to remove stock by horizontal cutting, primarily along the Z axis, typically from the right to the left. It is used for roughing out material out of a solid cylinder. It is available in two for mats—a one-block and a two-block format, depending on the control system. Older controls use a one-block format: N__ G71 P__ Q__ I__ K__ U__ W__ D__ F__ S__ where: P__ = first block number of the finishing profile, Q__ = last block number of the finishing profile, I__ = distance and direction of rough semi finishing in the X axis—per side, K__ = distance and direction of rough semi finishing in the Z axis, U__ = stock amount for finishing on the X axis diameter, W__ = stock left for finishing on the Z axis, D__ = depth of roughing cut, F__ = cutting feed rate per revolution, S__ = spindle speed in ft/min or m/min (cutting speed).
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