If you’re like most machine shops, you want to cut faster and hold better accuracy on your machining centers-without having to invest much money. Well, the means for doing just that could already be sitting in your shop. One of the best-kept secrets in the industry is that most modern CNCs contain many performance-enhancing features that builders of general-purpose machines often don’t use. All you need to do is turn them on.

“CNCs have a lot of capability that’s not taken advantage of,” says Bill Griffith, CNC product manager, GE Fanuc Automation North America Inc. (Charlottesville, VA). “You can hire a service engineer to set them up for you. Sometimes maintenance engineers learn about some features in the training classes that they take.”

The availability of these performance enhancements varies widely with the make of the CNC and its manufacturer’s marketing strategy. Some manufacturers, for example, activate all of the features that they offer, making them available to users from the outset to avoid “optioning” them to death. You just need to learn to use them. Others, however, price their products based on the active features, requiring their customers to pay only for those features that they use. So if the builder of your machine djd not activate a feature that you might find useful, you will need to buy it.

Although the cost of such features usually runs between $900 and $2000 each, it varies by manufacturer and type of feature. Sometimes the purchase is simply a matter of giving the CNC manufacturer your credit card number over the phone, and receiving an activation code that you punch into the CNC. Other times, however, a technician needs to come to the machine to activate and tune the feture, and perhaps even load a missing piece of software. In these cases, you’ll need to add the cost of the service call, which usually requires from a few hours to a day.

Keep in mind, however, that using these hidden features isn’t always just a matter of turning them on. Sometimes there is a tuning, or commissioning, process. Other times, you need to tweak cutting programs and internal software to account for the changes made by a feature. “You have to be aware of what you are doing to enhance your machine, because it might affect how the machine will operate,” says Christian Kuhls, CNC product manager, Siemens Energy and Automation Inc. (Elk Grove Village, IL).

An example is the motion-synchronous actions, or synchronized actions, feature in Siemens’ CNCs. This feature allows users to program instructions-such as sending output of auxiliary functions to the PLC, writing and reading of real-time variables, making on-line tool offsets, taking measurements, and calculating of function values-that are processed synchronously with the interpolation cycle. The goal is to complete tasks or to provide data in time for use. Since you integrate these actions into the machine and coordinate them with the tool motion, you might need to adjust them if any features change the machine.

To help users sort through the various features that are hiding in the CNG and to decide which would boost the performance of their machines the most, GE Fanuc’s Griffith suggests organizing them into a kind of hierarchy-one that puts sound mechanics at the base. Although software and electronics might mask some mechanical defects, they cannot make an unsound machine sound. The hierarchy then builds on the base of sound mechanics, beginning with servo and positioning adjustments, continuing with features that enhance the machine’s acceleration (and deceleration, which is nothing more than negative acceleration) and programming, and ending with those that add functionality to the machine.

At the lowest level, adjusting servo and positioning parameters, the first order of business is tuning the velocity loop. The process involves determining the natural frequency of the machine, which tells you the performance limits of the machine and lets you set resonance filters, velocity loop gain, feed-forward coefficient, and position gain accordingly. GE Fanuc has software called Servo Guide that leads users through this initial tuning process.

“Servo-tuning functions like feed-forward control are in every CNC, but aren’t always used,” says Griffith. “The feed-forward function more or less skips the position loop and sends the command directly to the velocity loop of the servo system.” By bypassing the slower position loop, the feature hastens the CNC’s response to any deviations from the programmed toolpath, allowing the machine to react to corners and contours much faster. Consequently, feed-forward control reduces any position errors that would result from servo-processing delays when cutting at high feed rates.

A feature called nanometer command interpolation allows Fanuc CNCs to send commands to the servo system in increments that are a thousand times smaller than before. These tiny, nanometer-size command increments not only improve accuracy by moving rounding error to smaller decimal places, but also make acceleration smoother, which allows you to cut at faster rates.