If you are experiencing excessive machine down time with a machine that is mechanically sound, perhaps it's the control system that is obsolete.

Rather than tossing your old machine and getting a new one — which can be a costly endeavor — consider retrofitting the computer numerical control (CNC). This process entails the replacement of the CNC, servo motors and drives, spindle system and associated wiring.

Retrofit costs are typically between one-third and two-thirds the cost of a new machine, according to an American Machinist Webcast. It also avoids the "hidden costs" of new equipment such as transportation, tooling, training and start-up times.

Steve Colasanti, systems integrator at Dual Electric & Refrigeration Services, agrees, saying in a recent case study at Modern Machine Shop:

The cost of upgrading a machine tool to almost new is typically a fraction of the cost of buying new. If you have a solid machine base to work with, retrofitting machines with digital CNC and servo technology can yield large decreases in cycle time while providing accuracy similar to that of new machinery.

According to the Webcast, along with being less costly than new machinery, other benefits of a CNC retrofit include:

• Typically a 20 percent increase in performance due to the faster CNCs, higher-speed motors and machining technologies;
• Machine electricity usage reduction by as much as 50 percent;
• Increased plant capacity because of smaller CNCs;
• Improved mean-time to repair and mean-time between failures; and
• Better data accessibility and support through upgraded Ethernet communications.

To determine the full value of a retrofit, the Webcast instructs shop owners to perform a standard return on investment (ROI) analysis of the anticipated revenue improvements and the savings from cost reductions in conjunction with all quoted and hidden costs of the project.

While the benefits are appealing, there remain a few key considerations to keep in mind before committing to a retrofitting project. One of these is that benefits will be delivered only by upgrading the servo and spindle system to a high-speed digital interface as well. "It does not matter how fast the CNC can process blocks of part program data if the servo and spindle systems cannot keep up," according to American Machinist earlier this year.

When you've decided to commit to the project, the first step is to investigate the mechanics of the machine and determine the feasibility of a digital upgrade, Modern Machine Shop suggests. "Proper inertial matching calculations for each axis drive system is essential to peak high speed operation," Colasanti adds. Next, the retrofitting project manager must get an understanding of the electrical system so the retrofitted CNC can be integrated properly.

Once the viability of a retrofit has been established, it's time to select a retrofitter or retrofit kit provider. A retrofitter selects the CNC and determines the correct-sized drive systems, writes the programmable machine controller (PMC) ladder, mounts and wires electrical components and motors, sets the machine parameters and does basic servo tuning, Bruce Vernyi at American Machinist writes.

Due to their numerous responsibilities directly tied to the success of the retrofit, it is important to be extremely selective when selecting a retrofit partner. The American Machinist Webcast suggests machine shop owners:

• Establish their potential partner's competency in machine type;
• Ask for documentation of quality;
• Ask for references;
• Get multiple quotes; and
• Make apple-to-apple comparisons.

Some red flags to watch out for when appraising the quotations are a disproportionately low price, smaller servos or spindle systems and a poorly detailed quote.

Once you've chosen your partner, make sure to specify the exact CNC model you need and want, plus all the optional contents and additional enhancements you require, the Webcast presenter adds.

Resources

Best Kept Secrets of Successful Retrofits Webcast
American Machinist, May 20, 2008

Retrofits Invigorate Old Machine Tools
Modern Machine Shop, May 29, 2008

Considerations when Retrofitting, Rebuilding or Remanufacturing Machine Tools
by Bruce Vernyi
American Machinist, June 11, 2008