Retrofit brings old floor-type mill up to modern standards

NUM’s CNC technology helps bring an old-floor type horizontal boring mill up to state-of-the-art standards, areas improved include programming software, motion control system.


NUM's CNC technology has been used to bring the programming software and motion control system on an old floor-type horizontal boring mill originally manufactured by Gray up to state-of-the-art standards. NUM CNC Technology

The electrical upgrade was performed by the automation system integrator, MasterControls LLC Inc. (MCI), and was part of a complete mechanical rebuild of the mill by a major US machine rebuilder. The machine is now in production with an end-user working in the mining industry.

The mill - which has a massive 42-foot travel on the main horizontal axis and weighs over 100,000 pounds (>45,000 kg) - had originally been converted from manual to CNC operation back in the 1970s. However, the control system was primitive by today's standards, with numerous drawbacks including limited CNC functionality, a very small memory size, and no networking capability.

MCI and its rebuilder customer performed an extremely comprehensive electrical and mechanical rebuild on the mill - even adding a secondary x-axis. By choosing a NUM CNC kernel, MCI has been able to bring the mill's CNC functionality up to modern standards. New capabilities include compatibility with RS274 G-code programming, probing functionality, and an industrial PC front end providing unlimited program storage - as well as networking.

MCI's introduction of a tandem drive arrangement on the x-axis has made a major contribution to the machine's performance and accuracy, increasing torque dramatically for the main axis of the machine. The two axes are now synchronized in a master-slave arrangement, with the new secondary axis set to lag the primary axis very slightly in order to maintain tension in the geartrain and eliminate backlash.

The flexibility of the drives and control software that allowed this configuration was an important reason behind MCI's decision to base the upgrade on NUM technology, as its drives support master-slave architectures. As this was a critical element of the project, MCI visited NUM's facility in Illinois during the development of the control system to physically test the tandem control, as well as to get the CNC vendor's feedback on MCI's proposed control and programming scheme.

Improving the underlying precision and accuracy of the heavily-built mill was a major feature of the control system upgrade, and MCI additionally implemented a table with laser measurements of axis positions to compensate for other variations in the mechanics.

Other key factors in choosing NUM's CNC system was the ability to upgrade the servomotor drives to advanced digital operation with absolute feedback - enhancing precision a step further. This also eliminates the need for homing moves - freeing the end user from having to reference the machine on power loss or after shutdown. NUM

All of the control system engineering and panel building was done off site. When the retrofit control system was complete, MCI took the package to the customer rebuild site and started installation. This phase was achieved in just three days. After testing and training, the whole machine was then disassembled and shipped to the end user.

According to Jeff Petry, MCI's Managing Partner, "The refurbished mill now has both a machining accuracy and a rich programmability that is comparable with a brand new mill - but at a fraction of the cost. The technical support available from NUM, who partner with us on applications like this, makes us comfortable taking on these types of major projects."

"Strong engineering support, and a partnership approach has always been a major element of NUM's business philosophy," adds Steve Schilling, General Manager of NUM Corporation in Naperville, Illinois. "It's one of the reasons behind the company's success with small to mid-sized machine tool OEMs, and system integrators and upgrade specialists such as MCI."


- Edited by Gust Gianos, CFE Media, Control Engineering,

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