Multitasking: Where High Requirements Meet High Volumes

In 2003, Metri-Tech Engineering found itself with a problem: The screw machine it bought to produce three high-volume medical parts couldn’t produce the geometries. After several months attempting to make the job work, it ultimately needed to use lengthy, multistep processes with single-spindle lathes to produce the order — not a great fit for a high-precision shop looking to expand from prototype jobs into production orders.

The rigidity of Metri-Tech’s Nakamura-Tome machines give the shop the capability to meet tight tolerances under 0.0001 inch, while dynamic and eccentric milling capabilities sharply cut cycle times and setup times. Images courtesy of Metri-Tech Engineering.

This problem led COO Hans L. Gratzer to approach his father, the founder and CEO of the company, with a pitch to buy something new for the shop: a Nakamura-Tome multitasking machine. This machine proved successful enough that the shop now uses ten of them, taking advantage of their rigidity, advanced cutting features and done-in-one architecture to cut down on setup time and cycle time alike.

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Making the Move to Multi-Tasking

Metri-Tech got its start working on prototyping and developmental precision parts that could fit in a person’s hand. These parts can be as small as 0.0625-inch in diameter, with tolerances typically around ±0.0005 inch — though today, the shop can achieve tolerances under 0.0001 inch if needed. Even its parts with seemingly looser tolerances can require closer attention to dimensional stack-ups, requiring even tighter tolerances. Production volumes for the shop’s prototyping and developmental parts typically range between 50 and 200 parts per run. But some customers, in particular customers in the medical, defense and industrial fitting industries, can require annual part runs into the thousands.

Gratzer’s father bought a screw machine from the shop’s typical OEM to tackle three high-volume medical parts, working with a skilled machinist to create tool paths that could properly machine the parts’ shapes. Unfortunately, the part geometries proved outside the machine’s capability range, and the shop machined the parts through time-consuming processes on single-spindle, single turret machines to fulfill the order.

Even before this incident, Gratzer had been pushing for the shop to begin working with larger parts at higher volumes. To do so, he wanted a multitasking machine, and the Nakamura-Tome machine hit a sweet spot of size and rigidity to help with the shop’s parts. After the screw machine proved unable to produce some of these parts, Gratzer pitched the Nakamura-Tome machine to his father and successfully got a WT-250Y onto Metri-Tech’s floor.

New Features, New Parts

Gratzer says the WT-250Y was Metri-Tech’s first truly automated machine when it arrived at the shop. The twin-spindle, twin-turret setup with live tooling and Y-axis machining capabilities gave the machine more flexibility than the shop was accustomed to using, plus it was the shop’s first machine with chip conveyors, tool length offset capabilities and high-pressure coolant on its spindles. While its rigidity proved useful right away for the shop, Gratzer says it took two years before the shop fully trusted the machine’s advanced features and fully utilized both turrets. During the first few months, it only used one turret at a time. Gradually and cautiously, the shop experimented with simultaneous pinch turning and pinch milling, which helped maintain tight concentricity and straightness on long, slender parts and cut cycle times by enabling simultaneous roughing and finishing operations. Pinch turning also helped the shop reduce setup times by eliminating the need for steady rests and centers from some operations, making the shop more agile and efficient as it increasingly takes on annual part volumes between 5,000 and 15,000 pieces for medical, defense and industrial fitting customers.

The Nakamura-Tome machine also facilitated Gratzer’s desire to work on larger parts, and as the shop has installed more Nakamura-Tome machines, it has increased its maximum part size to a 36-inch cube. Metri-Tech now uses 10 two-spindle multitasking machines from the company, as well as some one-turret and three-turret machines. Gratzer points to the NTY³-250 and the JX-250 as the shop’s new centerpieces. The former is a three-turret multitasking machine, while the latter uses a five-axis, 30-hp milling head; dual spindles with a 65-inch spindle-to-spindle distance; and two turrets. The turrets on the JX-250 support half-indexing and can each hold 48 standard tools or 24 live tools.

Metri-Tech has instituted policies to ensure all changes to part programs take place in the programming department. This prevents issues with outdated programs and helps with traceability for high-requirement jobs.

These machines support the shop’s ongoing operational consolidations by enabling more done-in-one processes. In particular, the five-axis capabilities of the JX-250 enable “a true mill-turn platform — one where the milling capabilities are just as advanced and robust as the turning,” he says. Previously, parts with complex milled features or multiple milled faces required a secondary machining operation on a separate machine after initial turning. This not only extended cycle and setup times but also introduced the risk of tolerance stack-up and alignment errors due to re-fixturing or relocating to a different machine. With five-axis milling now integrated into the multitasking platform, Metri-Tech has significantly reduced the need for multiple setups and fixturing. Gratzer notes that this improvement has had a substantial impact on repeatability, throughput and overall process efficiency, especially for high-value, low- to mid-volume components. In many cases, the shop has achieved cycle time reductions of 30–50% with setup time reductions of up to 75%, depending on part complexity.

Beyond raw capabilities, these cycle time and setup time reductions also stem from the advanced machining techniques the machines support. Dynamic and eccentric turning have been particularly impactful for the shop. In dynamic turning, programmers can adjust the approach angle of the cutting tool mid-operation. For tools with different cutting edges suited to roughing, profiling and finishing, this can also mean performing all these operations without tool changes. Gratzer says the shop uses this capability to machine complex grooved and radiused profiles with a single tool, which cuts cycle times and improves surface consistency. Eccentric turning enables the shop to machine off-center bores without specialty off-center workholding, eliminating the cost of custom fixturing and workholding while improving productivity, accuracy and setup time. Gratzer goes so far as to say the combination of dynamic and eccentric turning is vital for the shop. “Both of these are fairly new features in the turning world that we just cannot live without,” he says.

Bonus Features

Gratzer expected the Nakamura-Tome machine to expand the shop’s capabilities to larger parts, but he did not initially expect it to help the shop gain a foothold in gear cutting. As the number of shops capable of working with gears has decreased in the U.S. (and especially around Huntington Beach, California, where Metri-Tech is located), Gratzer says that taking gear work in-house was necessary if the shop wanted to keep these jobs. The advanced manufacturing capabilities and construction of the Nakamura-Tome machines enabled the shop to perform this work, while also enabling the shop to better control lead times and quality compared to outsourcing.

Implementing gear cutting or the newer dynamic and eccentric turning features has also gone more smoothly for the shop than its initial introduction to pinch turning. This is largely down to the shop’s heavy use of simulation software. Metri-Tech is careful to ensure that digital twins in its CAD/CAM simulation software, Hexagon’s Espirt Edge, match the physical machine and its kinematics, so every tool index or collision risk that could appear on the floor is anticipated and addressed in the programming office. In fact, the shop goes so far as to require all changes to be made in the programming department and synced wirelessly with the machine. This ensures proper revision control, preventing successful cutting parameters and programs from being lost and ensuring standardization and traceability for Metri-Tech’s high-requirement customers.

Servicing an Ever-Increasing Pace

As these complex machines touch nearly every part that crosses the shop floor, downtime could significantly hamper Metri-Tech’s operations. Thankfully, Gratzer says, the Nakamura-Tome machines rarely see downtime, with most of it due to user error or lack of maintenance. Even in these situations, he draws attention to a Nakamura-Tome troubleshooting feature that displays pictures on the control of likely problem areas when the machine alarms out. Operators can check the pictured area to quickly bring the machine back online in simple cases — such as a relay error or an error with oil levels — reducing the number of scenarios where the shop must contact its distributor, Methods Machine Tool, for a service call.

To meet the production levels necessary for its newer jobs, Metri-Tech runs two 12-hour shifts: one staffed, one unstaffed. The shop deploys several cobots that it can redeploy around the shop floor as necessary, as well as a 240-pallet five-axis pallet system. These and the machines have helped spurred the shop to grow by 250% over the past eight years, numbers the shop plans to raise even further through mobile robotics, a custom ERP and continued investment in capable machines.

Qualified for Quality

Metri-Tech Engineering maintains specialized inspection and verification equipment to meet its customers’ stringent quality requirements. Most recently, the company integrated a 3D blue-light scan box with precision photogrammetry, specifically designed for inspecting castings and forgings as well as for reverse-engineering legacy components, particularly those lacking 3D models or engineering drawings. These capabilities eliminate the need for customers to outsource scanning, streamlining the workflow and reducing lead times. The automated scan system enables rapid validation of parts directly from casting houses or suppliers, confirming dimensional conformance to customer-supplied models. This early-stage verification prevents non-conforming material or parts from advancing into more time-intensive or costly machining stages.

Metri-Tech recently bought a 3D blue-light scan box. This makes inspecting castings and forgings much simpler, enabling the shop to confirm dimensional conformance for these kinds of incoming parts before moving these parts to time-consuming or expensive machining processes.

Additionally, Metri-Tech employs an XRF (X-ray fluorescence) scanner to verify incoming raw material. This ensures that the material type and chemical composition precisely match customer specifications and certification documentation. By identifying discrepancies at the point of receipt, the shop can prevent material-related errors early in the process, saving significant time and cost while safeguarding product quality.

Gratzer says that Metri-Tech performs a full first-article inspection for each new order placed from its customers, regardless of if the setup changed, with frequent reinspections to ensure continued quality. Single inspectors examine parts the shop has run before, while pairs of inspectors are required to inspect and sign off all new parts. Gratzer says the shop’s staff has a deep foundational knowledge of the physics behind manufacturing, so they have a good idea of what precautions will help them avoid common pitfalls. The shop also takes the time to bolt down machines and follow OEM recommendations for foundations, performs ball bar testing regularly and calibrates its machines yearly.

Metri-Tech’s emphasis on quality is also reflected in how it deploys its employees’ deep understanding of machining and physics in the area of EDM. The company began using wire EDM in the late 1980s to manufacture custom carbide boring tools for complex geometries that could not be machined using conventional methods and for which tools were not readily available. As its capabilities expanded, Metri-Tech applied wire EDM to produce close-tolerance components for the defense sector. The shop also adopted sinker EDM to remove broken carbide tools from titanium and Inconel parts, an operation which otherwise required costly outsourcing.

Over time, Metri-Tech has gained expertise in both technologies. The shop now promotes its ability to direct sparks in wire EDM to avoid creating a heat-affected white layer, which is prone to microfractures. This level of process control is critical for high-reliability applications. Gratzer points to one case in which one of the shop’s medical customers briefly changed providers to a lower-cost supplier to produce its parts. When its parts quickly experienced failures due to the introduction of a heat-treated layer during the EDM and grinding processes, the customer quickly returned to Metri-Tech.