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CNC Machining Advantages

The main advantage that CNC offers here is that it takes over the physical control of the equipment once the job has been set up and automatically completes it, freeing up the operator to perform other tasks. It’s like multiplying the work that one man can do without having to hire extra employees or work overtime.

By Larry Carley

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Running a profitable machine shop these days requires a lot of things: skilled machinists who know what they are doing, accurate equipment that can perform all of the tasks that are required to machine cylinder heads and blocks, an efficient work environment that maximizes both shop labor and equipment usage to boost productivity, a commitment to quality, and a loyal customer base. So how does Computer Numeric Controlled (CNC) machining fit into all of this?

Let’s start with the skilled machinists who operate the equipment in your shop. A good employee who knows what he’s doing can complete a certain number of jobs during an 8-hour work day. His productivity is limited by how much time it takes him to set up each job and how long it takes him to complete each task.

Accuracy, repeatability and an overall improvement in consistency and quality are additional benefits that CNC can provide. With a multi-purpose CNC machining center, there’s no need to move a work piece from one machine to another to complete different tasks.

Once you’ve mounted the head or block in the fixturing, you can perform multiple operations without having to move, remount and reset the parts. This reduces the chance of making a mistake and saves a tremendous amount of setup time.

Uncovering The Myths of What CNC Is and Isn’t
Some people call CNC machines “smart” machines because of all the things they can do. But a CNC is only as smart as the person who programs it. The computer that controls the motions of the tooling and part that is being machined is only following a road map that tells it what to do and how to move.

A human operator has to enter the commands that tell a CNC machine what to do either via conversational (question and answer) programming on a computer touch screen, or by entering G-code or M-code, which is the underlying language that CNC actually uses to control the movements of the tooling and parts fixturing.

The main advantage with CNC is that once you have entered the necessary instructions to perform a particular job, mounted the part to be machined in the fixturing and zeroed its position relative to the machine tooling, CNC takes over and does everything else. You don’t need an operator to run the equipment or to babysit it.

And if you are performing the same job over and over again on a run of similar parts, CNC will do each job exactly the same every time with a higher degree of repeatability and precision that is normally possible on manually operated shop equipment.

Of course, CNC isn’t foolproof. If an operator makes a mistake while entering the programming information for the job (like misplacing a decimal point or entering a wrong number), it may cause the tooling to move too far causing a crash that may ruin the work piece, break the tooling or even damage the equipment!

To minimize the risk of equipment damage, most CNC machine suppliers build in some type of collision avoidance crash protection that will prevent tooling from overextending its normal range of travel, or sense when an axis motor is overloading and immediately shut down the equipment before any serious damage can occur.  But you can still ruin a work piece if you mistakenly tell the CNC machine to do something it shouldn’t do, like drill a hole in the wrong place or too deep, or mill off too much metal from the surface of a head or block..

How CNC Got Its Start
Following World War Two, the aviation industry was looking for better ways to machine and automate the production of complex components for military and civilian aircraft. In 1952, the United States Air Force (USAF) asked scientists at the Massachusetts Institute of Technology (MIT) to come up with some type of control system that would make this possible.

One of their solutions was to use punched paper tape to control the movements of existing industrial machine tooling. The holes in the tape told the equipment how to move so it could machine the desired shapes. The new “numeric control” concept took awhile to catch on, but eventually it became quite common in all kinds of industrial manufacturing plants.

In the 1970s, the development of electronic computers allowed numeric control to be integrated with digital and analog processors. This eliminated the paper tape input, but still required a high level of skill to program the G-code and M-code that actually controlled the movements of the machines.

The development of better graphic interfaces for display monitors, touch screens and conversational programming made it possible to program CNC equipment without having to know any G-code or M-code commands. This opened up all kinds of new applications for CNC machining and brings us to where we are today.

How Hard Is It To Learn CNC?
Not very, according to most of the CNC equipment suppliers we spoke with for this article – at least for basic tasks. There are three basic aspects of CNC you have to understand: how to setup the parts on the machine, how to setup the tooling on the machine, and how to program the machine so it will do what you want it to do.

In a smaller shop, typically the operator will do all of these steps himself. But in a larger shop (especially if the shop has multiple CNC machines), one person may do all of the programming allowing less skilled operators to run the equipment.

According to one CNC machine supplier, their unique conversational programming is so easy to learn that a skilled machinist who knows how to use a micrometer and read a blueprint can be operating a CNC block center after only three hours of introductory training. In other words, you don’t need any CNC or programming experience to operate a CNC machine. Of course, the training requirements will vary with the CNC equipment and the simplicity or complexity of its programming interface.  Some are easier to learn than others.

Most CNC controls use a computer monitor or touch screen to enter information, either in a menu format or conversational Q&A format. It’s fairly intuitive and easy to understand. Some screens may show a 3D graphical display to illustrate how the tooling will travel once it has been programmed, and where the tooling is moving during the job itself. 

As a rule, most machinists can learn how to perform basic jobs on CNC equipment after a few days of training.

Most CNC suppliers provide training (often at your place of business) when they install a new CNC machine.  Others have a central training facility or use regional training facilities. If your shop already owns a CNC machine or you have people with CNC experience, your employees may only require minimal training on how to program and use the new CNC equipment.

On the other hand, if you or your employees have no CNC experience, it may take awhile to become fully competent with all of the nuances of CNC machining and many of the things it can potentially do (like 5-axis porting of cylinder heads). One CNC equipment supplier said learning the basics of a 3-axis machine is fairly simple because you are only dealing with three directions of movement: X and Y (sideways in two directions) and Z (vertical).

With a 5-axis machine, however, you also have to understand the movement of the A axis (which is the rotation of the tooling toward or away from the work piece) and the B-axis (tilt of the workpiece).  And if you also want to do your own CAD/CAM design work for manufacturing your own parts, the learning curve can be rather steep taking 6 months to a year or more to become highly competent in all aspects of CNC and CAD/CAM. Fortunately, you don’t have to be a computer expert or know anything about CAD/CAM (Computer Aided Design and Manufacturing) to do most of the common machining operations on a CNC machine.

“Teaching a new operator how to fixture blocks, what tools to use and how to set them takes up the majority of the training time, which usually lasts 5 days,” said one CNC equipment supplier. “Generally by second day the new operator has the controls and is operating the machine by himself with our technician watching over them. By the end of the week the operators are confident and ready to go!”

What are the hardest aspects of the CNC machine to learn? “To trust the equipment,” said the same equipment supplier. A CNC machine will do exactly what you tell it to do. You just have to make sure the numbers you enter into the CNC controls are accurate and that you haven’t made a mistake.

One CNC trainer said he typically trains a new CNC operator to first cylinder bore and then surface. Once they are comfortable with those functions, they can move on to lifter boring and stroker clearancing. After that, they can learn to do block end truing and line boring. If they want to do cam boring, install 4-bolt main caps or machine a new style block so an older mechanical fuel pump can be mounted on it, that comes next. All of this can be learned in 5 days of training or less.