Not the Same, Old Boring Mill Story

Feb. 3, 2011
CNC retrofit brings old floor-type mill up to modern standards
NUM's CNC technology was used to upgrade the programming software and motion control system on an old, floor-type horizontal boring mill to state-of-the-art standards.

With the right design and technology, even “old” machine tools can be updated to advanced processing capabilities. 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 G.A. Gray) up to state-of-the-art operating standards.

NUM develops CNC controls and designs and manufactures drives and motors. It also performs CNC and system integration with third-party products in cooperation with other suppliers and customers. In the case of the Gray horizontal boring mill, the electrical upgrade was performed by MasterControls Inc. LLC (MCI), and was part of a broader mechanical rebuild. The machine is back in production now for a shop that serves a mining industry OEM.

The mill, which has an impressive 42-foot travel on the main horizontal axis, and weighs over 100,000 lbs., was converted from manual to CNC operation in the 1970s. However, that CNC control system was primitive by current standards, with a variety of drawbacks including limited CNC functionality, inadequate system memory, and no networking capability.

MCI and the mechanical contractor performed a comprehensive electrical and mechanical rebuild, including adding a secondary x-axis. MCI’s decision to incorporate a NUM CNC kernel was critical to bringing the mill's CNC functionality up-to-date. The redesigned system is compatible with RS274 G-code programming, has probing functionality, and features an industrial PC front end that provides unlimited program storage and networking capability.

MCI's introduction of a tandem drive arrangement on the x-axis has been a notable factor in the machine's performance and accuracy, increasing torque dramatically for the main axis of the machine. Now, the two axes are 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 gear train, and to eliminate backlash.

The flexibility of the drives and control software that allowed this configuration was an important factor in MCI's decision to base the upgrade on NUM technology, as its drives support master-slave architectures. MCI performed physical testing of the tandem control at NUM's operation in Naperville, Ill., and also consulted with the CNC on the control and programming scheme.

NUM's advanced digital servomotor drives with absolute feedback were used for the mill’s modernization.

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

Other factors recommending NUM's CNC system was its ability to upgrade the servomotor drives to advanced digital operation with absolute feedback. This certifies its precision control capability and eliminates the need for homing moves, freeing the operator from having to reference the machine on power-loss or after shutdown.

All of the control system engineering and panel building was done off site. When the retrofit control system was complete, MCI delivered the package to the rebuild site and installed it in just three days. After testing and training, the whole machine was disassembled and shipped to the machine shop.

According to MCI managing partner Jeff Petry, "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."

MasterControls Inc. LLC, in Pendleton, Ind., is well known for its machine tool automation upgrades. The system integrator has more than 25 years of experience at replacing legacy CNC systems on lathes, mills, grinders, gear hobbers and other capital equipment. One reason for its success in the U.S. machine rebuild market is its willingness to conserve costs by retaining analog-interfaced servomotor drives on CNC systems (though, not in the current project, where the customer specified optimal precision for the rebuilt mill.)

The rebuilt machine is controlled by a custom-designed screen created using NUM's NUMpass software.

MCI relies on close relationships with a number of control system equipment partners, including NUM for CNC applications. "Strong engineering support, and a partnership approach has always been a major element of NUM's business philosophy," according to Steve Schilling, general manager of NUM Corp. in Naperville. "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."

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