Cutting large stone slabs into high-end kitchen countertops, reception desktops, and other decorative interior and exterior fixtures takes tough machinery and a lot of power and control. However, the hardest challenge facing the stonecutting industry isn’t cutting through solid marble or granite: it’s doing so with maximum productivity, precision, and efficient use of raw materials. Recently, a leading US stonecutting tool builder Advanced Industrial Machinery (AIM) redesigned one of its top products, the MasterJetSaw combination cutting saw/waterjet system, to reduce design/build costs and significantly improve stonecutting throughput and productivity. To achieve these goals, AIM incorporated a new drive and control system, a CNC machine control platform and an integrated motor and drive system, all supplied by Bosch Rexroth Corporation.

The MasterJetSaw is AIM’s top of the line tool, designed for highthroughput stonecutting for major commercial and residential stone surface applications (Fig 1). Combining a rigid, high-accuracy 20 hp rotary cutting head, high-speed diamond-tipped blade, and a 50 hp abrasive waterjet cutter into a single unit, the MasterJetSaw lets fabricators cut accurately and repeatedly in stone up to four-inches thick. Most cuts are straight, using the 20 hp rotary saw. The waterjet is used for radiuses, sink cut-outs, holes for pipes and fixtures, and other circular or curved cuts. Until recently, AIM built waterjet and saw machines at its Hickory, NC factory using conventional servo drives and motors. The company were looking for new technology that would:

Reduce machine footprint

Lower machine component costs

Reduce the time to build machines and deliver to market

Improve stonecutting productivity and materials utilisation

AIM worked with Livingston & Haven (Charlotte, NC), a leading supplier of manufacturing productivity technology solutions, and a major distributor of Bosch Rexroth products, to identify the best solution to satisfy their requirements for the MasterJetSaw. AIM and Livingston & Haven chose to upgrade the machine with the Rexroth IndraMotion MTX CNC platform and the IndraDrive Mi integrated servomotor and drive system, for a complete drive and control solution.

New CNC system

The MasterJetSaw has four axis of motion. The cutting heads are mounted on a gantry for X and Y horizontal motion, the Z axis moves the cutting heads vertically in minute increments, and the C axis controls the rotary saw blade.

In stonecutting, the circular cuts are the most challenging – rounded edges, oval and circular holes for sinks and fixtures, curving details on stone surfaces. According to AIM’s Pharr, rounded cuts requires true closed-loop control of multi-axis interpolated motion – which is why Rexroth’s IndraMotion MTX CNC system was chosen for the machine control. IndraMotion MTX is a high-productivity machine tool CNC that contains all the components – drives, controller, operator software and a powerful engineering framework – optimised for machine tool automation. It can support up to 64 axes of motion and 12 independent CNC channels, providing the shortest CNC cycle times and minimum PLC program processing times. This helps tool builders achieve high-speed machining and reduce non-productive setup and changeover times. The MasterJetSaw uses the MTX platform running on a Rexroth 15-inch IndraControl VSP model industrial PC. The controller communicates via SERCOS III to a Rexroth 70-amp IndraDrive drive unit and Rexroth KCU unit, from which a single cable system runs carrying DC bus, power, control power and communication to the integrated motor and drive servo axes.

'A lot of companies claim they can do controls, but all they can really do is point to point process control. Process control and interpolated motion of multiple axes are two totally different things.” Said Bob Pharr. “Rexroth proved it could cut a radius at high speed, with a high degree of accuracy, and then match that cut with a different tool or a different size, with the highest levels of throughput.”

A critical method for getting the most material from each slab is called “nesting” – cutting as many different countertops, facings, and other finished products as possible out of one rectangular 6- by 10-foot, or 7- by 12-foot slab. It’s akin to cutting out the pieces of a jigsaw puzzle.

In the past, tool operators had to leave three inches of space between each piece to be cut, to make sure cuts for one piece didn’t end up cutting into another countertop. The MTX precisely controls the movement of the circular saw and waterjet to make sure each piece is cut properly with minimal waste and much greater accuracy. As a result, operators can space parts with much tighter tolerances, cutting more pieces from each slab.

'The parts are accurate to within four to five thousandths of an inch, far more accurate than what’s been done in the past,” said Pharr (Fig 3). “Because the original cut is more accurate, it speeds up the finishing process.”

Labour savings

One of the first companies to use the updated MasterJetSaw with the Rexroth IndraMotion MTX and IndraDrive Mi technology is Elite Installation and Designs, Inc. of Hendersonville, TN. Before using the MasterJetSaw, the company’s order book was so full that it was running at maximum capacity with high amounts of overtime – sometimes cutting until 9 pm. The MasterJetSaw has changed all that.

According to Elite president Chris Brown, within the first week of using the MasterJetSaw, they were able to eliminate overtime entirely, and were cutting so fast they moved five days ahead of their production schedule.

'The nesting alone is incredible - we virtually have crumbs for waste,” said Brown. “We’re cutting at 166 inches-perminute. In the first six hours of using the tool we cut ten slabs and pushed them through our CNC polisher. Our fabricators were looking at us like we were crazy,” he exclaimed. According to Bob Pharr at AIM, other companies that have recently begun using the MasterJetSaw calculate their return on investment to pay off within less than a year, and in some cases, half that.