The View From 1776

EDUCATION FOR CNC MACHINING

By Richard Becker

The Front Range Community College, North Campus, is contemplating shutdown of their Machining Technology program for the 2-year Associate of Applied Science Degree in programming, setting up and operating computerized CNC (Computer Numerical Control) machine tools of manufacturing. A problem created by failure of the high schools, failing to introduce students to CNC as a potential career option that requires the identical high school education as college preparation, on the assumption that the core basics of reading, writing and math are not essential for acquiring “manual vocational skills”! And, failure to properly teach them reading, writing and math as essential for gaining skills and knowledge.

CNC is a process where a computer built into each machine operates the machining procedure digitally via servomotors and other electronic devices replacing manually operated machine tool controls of the past. A “high tech” concept that has existed since 1977, and requires Information Technology combined with machining practices and core knowledge to create a machining “program”. In this case, programming is a matter of inserting in the proper sequence the codes to instruct the computer which machining sequence to select in the proper order.

An academic high school education has always been essential in the machining/manufacturing industry. A 1951 second edition textbook MACHINE SHOP MATHEMATICS for high school graduates as vocational and apprenticeship students seeking machinist skills and knowledge. Chapter 1 Shop Arithmetic states in the opening paragraph that “Arithmetic is the basis for all mathematics”. The last paragraph states: “This chapter will deal with a review of the principles involved in the solution of shop problems concerned only with fractions and decimal fractions, since it is assumed that those who will use this text will have mastered the four fundamental operations as applied to whole numbers" ; addition, subtraction, multiplication and division! (emphasis added). Chapter 7 Geometric Construction teaches geometric principles as the basis of machine drawings. Chapter 8 Shop Trigonometry states: “Trigonometry, as far as the apprentice is concerned, deals with the solution of right and oblique triangles. He will find many applications of trigonometry in his daily work, especially angle boring and tapering”. It addresses the solution to problems using the trig tables or the Pythagorean theorem.

When the above textbook was found in a thrift store, it contained a 3-page, neatly typed report on “Gear Cutting, showing that written communication is essential. The report was critiqued by the instruction as per an English or other academic field instructor going over homework assignments.
It also contained a folded sheet of notebook paper covered on both sides with mathematical calculations, either from doing the exercises at the end of the math chapter, or using the text for reference on the job and performing math calculations when setting up a machining production job.

Existence of a textbook illustrates that reading and reading comprehension was essential in acquiring core machining knowledge in preparation for each class, and applied in the direct labor workplace. No different in principle in accepted academic courses, where assigned chapters are to be read in preparation for the next class. Basic knowledge required to understand the instructor meeting with the class to explain and demonstrate the principles for that lesson. Then, students enter the lab containing machine tools and apply the concepts learned for reinforcement. A concept contrary to that of school officials who have assumed that academically deficient individuals become “machinists” by having an instructor showing them what button to push and when to push it.

The required Machining Technology textbook list, acquired from the Front Range CC bookstore, lists the “CNC Programming Handbook” by Peter Smid. A copy is available for checkout or review by anyone who wishes to verify its existence and content. See to view the text and a list of contents.

The book has a college level reading and reading comprehension requirement. It covers the basics of control panel functions. Chapter 4 Coordinate Geometry covers the principles of the Cartesian Coordinate system as the basic element of CNC machine tool functions. The work area of a vertical machining center is divided into four quadrants: Quadrant I X+Y+; Quadrant II X-Y+; Quadrant III X-Y-; Quadrant IV X+Y-! If that is puzzling, check the textbook and look on page 17 as students would do to understand it.

Chapter 52 Math in CNC Programming states, in a box for emphasis: “The knowledge of trigonometry is essential to any serious CNC programming”! Under “Basic Elements”, it covers Arithmetic and Algebra, followed by Order of Calculations (as applied to CNC) and Geometry as taught (presumably) in high school for college preparation purposes. On page 480, it teaches trigonometry as required in application to calculate unknown angles when setting up for machining an angle.

Scattered throughout the textbook are examples of programming for specific functions. for example, from page 403: N28 G90 G54 G00 X-2.5 Y-2.0 S4000 M03 T01 is a line of code for “XY start position for peripheral chamfering”! N28 denotes a line of code; G90 Absolute Dimensioning mode; G54 Work coordinate offset 1; G00 Rapid Positioning (of the work under the milling head in the Z axis); X-2.5 Y-2.0 coordinate location of beginning of the chamfer via the Cartesian Coordinates; S4000 rotational speed of the milling cutter in rpm, based on the ductility of the material, cutting lip angle, number of flutes of the milling cutter, and the finish desired; M03 Circular interpolation counterclockwise; T01Cutting tool #1 in the magazine.

The above is an explanation of just one line of code in a total of 44 lines in three blocks of machining information. Each block concerns use of a different milling cutter. In many cases, machining companies require a programmer/operator to program for a production run. Also, knowledge of codes is essential because operators are also responsible for editing the machining program codes to adjust it to maintain dimensions specified by the design engineer as per the drawing called a “print”. It is essential they know which line of code needs to be changed, and in which direction; - or +, to bring it into specifications.

The supervisor running the production facility has not the time to “babysit” an employee who has not the knowledge to setup, program, and operate the machine tool. When assigned a machine to setup, program and operate, he or she is expected to apply skills and knowledge to get the job done and produce the first item for the supervisor to check against the print and verify that it is in specifications before beginning actual production.

The most common CNC machining facility is called a “job shop” that takes in machining work by the “job” from companies who have a need for precision machined items assembled into their products but it makes more sense to job it out rather than go to the expense of setting up and equipping an in house facility. That includes manufacturers of computer “high tech” hardware such as disk drives, CDrom drives, hard drives etc. A “Job Shop” provides a MACHINING SERVICE ( part of the “service industry") and the supervisor is too busy bidding on jobs, ordering materials, and assigning machining jobs to be setup and run, and has not the time to be telling academically and CNC ignorant employees how to perform the tasks for which hired.

Many schools have adopted the Applied Technology, or similar program, involving a table-top CNC miniature milling machine and turning center to replace the old “shop” courses. It is assumed by many that the program produces students who can obtain good-paying jobs in machining. That is a perceptual fallacy, because there exists a huge difference between simple CNC machining concepts taught in applied technology courses and the real machines used in industry. Machines with multi axes dominate, and are more complex and more powerful than the “toys” used in schools to “teach job skills” though only serve to introduce students to the concepts of CNC machine setup, programming and operating.

Another major reason that an academic high school education is essential, is new machining businesses starting up. After working in a CNC programmer/operator capacity for a few years to get some solid experience, many go on their own to establish their own machining business. Perhaps buying a machine and installing it in their garage until business picked up and a larger space is reuired to house other machines and hire experience people as business expands.

Besides precision machinists producing machined components in quantity for assembly into consumer items such as computer hardware and other “high tech” items to “low tech” items such as aluminum castings for paint sprayers, there are tool and die makers, mold makers who use the identical machines to produce precision components for punching and forming dies, and moldmakers using the identical machines for producing steel molds used for producing precision plastic items by injecting melted plastic into the molds to form cellphone bodies and other items of a “high tech” and “low tech” nature. To many computer users, “hard drives” are “high tech” disk and CD roms, and CD burners are abstract items that merely “exist” or are but a slot into which a disk or CDrom or CDdisk is inserted to record or retrieve information, but fail to consider the mechanical device behind the slot.