MACH IN ERY
An introduction to CNC By Machinery Editor, Philip Ashley
A
lthough it appears that CNC manufacturing popped up yesterday, in fact it’s been over 60 years in the making. If you work with stone or other similar materials, CNC processing can be an extremely versatile method of producing benchtops in granite and marble but also for a range of other products such as cladding, tiling, shower bases and fire-place surrounds. CNC machines are still a large investment for most companies with $350,000 to $500,000 being a ball-park figure. They do, however, offer the potential for significant improvements in output and quality that far outweigh the initial cost. NC control came about as a result of the American military aircraft industry. At the end of the Second World War it was apparent that faster jet aircraft required more complex and demanding parts. Conventional means of manufacturing were falling short of the required tolerances and a faster, more accurate method of parts manufacture was needed. The movie “The right stuff ” chronicles the race to break the sound barrier and
conquer space and it is within this time frame that the history of CNC is set. During the late 1940s John Parsons was working on a system where punched cards containing position data controlled a machine tool. The idea was to machine flat templates to check the contour of helicopter blades. Parsons submitted his idea to the US Air Force in 1948 and was awarded a development contract with the University of Massachusetts (MIT) Servo Mechanisms laboratory. During the next three years a conventional milling machine was fitted with positioning servomotors for three axes (or movements) known as X, Y and Z and the first NC routing machine was born. The machine demonstrated in 1952 looked very similar to a modern-day single spindle CNC router. Different were the banks of computer consoles needed to drive the servomotors, almost equal in area to the machine itself. All this was driven from a punched paper tape, and became known as numerical control, or NC. Numerical control
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is where machine codes are used to “drive” the machine. There are codes to start and stop motors; move the cutter-head left, right, up and down; and other codes for feed speeds and spindle RPM, etcetera. Development in the woodworking industries began in the mid 1960s when the Ekstrom Carlson Company offered the first NC router in the USA. The Japanese Heian company developed its first NC router in 1968 and in 1969 Shoda claimed the first circular-cutting NC router. Early machines of the NC type relied solely on a punched tape. The paper tape had holes punched into it that the machine controller read as code. No calculations or modifications were possible on the computer and a new tape would be made even if only one code was changed. Computer numerical control (CNC) was not to follow until IBM developed the personal computer. The American Thermwood Company claims the first CNC machine, based on the Intel 8080 chip. Unlike NC, a CNC machine is able to perform some calculations