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Advances in Hand-Held Metrology

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

Easy to use hand-held contact devices for professionals and workers remain a mainstay in metrology and measurement. New developments in electronics and wireless data transfer are keeping them relevant as they become more accurate.

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Precision measuring instruments require regular recalibration, depending on use.

While high-end metrology devices like advanced laser scanners or precision CMMs garner a lot of attention, it is hard to imagine any industrial setting without the presence of work-a-day hand-held, contact metrology tools such as calipers or micrometers. That is what Justin Frazzini, quality manager for A.A. Jansson (Waterford, MI), retailer and calibration and repair service provider, observes in his practice. No matter the application, whether measuring a heart stent or surface roughness of soda cans, he notes there is a hand-held device to measure it to ensure quality.

Variety, High-End and Low-End

Look at any catalog and you can see the immense variety of such tools available. There is also a great variety in their uses, from individual spot checks to whole systems for statistical process control, or SPC. Metrology hand tools in particular are useful to operators of machining centers. “We often see that where there is a machining center, they have a hand-tool station set up with height gages, calipers, and micrometers for quick checks,” he explained. At the other end of the spectrum, Frazzini relates that A.A. Jansson has also sold a few complete systems for in-process manufacturing control. Digital hand tools today have an option to wirelessly connect to a central data center for SPC. “The wireless transfer systems today have improved, with more range to send data so you need fewer routers,” he explained.

This variety of uses and utility has shifted the market into two distinct categories. “There are the very expensive, accurate hand tools, and then ones that are less accurate that I call ‘throw away’,” he explained. The high-end require care and periodic refurbishment and calibration. The low-end, not so much. “They’re very inexpensive and you can just throw them out, because of the relatively low cost,” he said.

Even for the more expensive models, a worn gage will provide poor results. “We always recommend recalibration every year, but it really depends on frequency of use,” he said. A significant trend he sees in the calibration services his company provides is more on-site engagements for his company to travel to a factory and calibrate tools there rather than having them shipped back and forth from the factory to Jansson. “It’s easier for the customer,” he explained. A single Jansson professional with all of the company’s masters and equipment will recalibrate in a day the customer’s supply of calipers, micrometers, and other hand tools. “It is cheaper for the company because there is less overhead and it’s faster, they don’t have to fool with shipping labels and certification reports,” he explained.

Faster with Snaps and Air

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This high-accuracy micrometer from Mitutoyo is capable of 0.1-μm resolution measurement, showing a trend for hand-held tools getting ever more accurate.

George Schuetz, director of precision gages of Mahr Federal (Providence, RI) describes how the mix of hand-held gages his company provides has changed as industrial tolerances have increased. “Calipers and micrometers are, of course, by far the largest volume of hand tools sold, primarily because of their versatility,” he said. These are useful when tolerance specifications are greater than 0.05 mm or so. “You will see those at incoming inspection or near a general machining center where their tolerances are not too tight, but they have to perform many different checks,” he said.

When measuring tighter tolerances is needed, other hand-held options are needed. The next category in accuracy are fixed-variable gages. “When you start getting into measuring a 0.025 mm or better, then we get into a world of comparative-type gaging,” he stated. An operator sets a comparative gage to a specific dimension, usually by measuring against a master. Then they compare it to a part to see how much larger or smaller it is. Often, a go/no-go setting option is available directly on the readout. “Those types of gages are easier to use because they are fixed in one dimension. There’s very little operator influence on it and they’re faster to use, making them useful in high-volume production or near a machine tool where you are pumping out a lot of parts,” he said.

For even tighter tolerances, and more speed, air gaging is the right choice, according to Schuetz. These hand-held devices measure linear dimensions and are made to a specific size, say, two inches. He notes that they are the easiest to use and the most accurate, with measuring resolutions down to 0.2 μm for the company’s Dimensionair systems. For OD gaging, snap gages follow a similar philosophy, but measure cylindrical components. Mechanical snaps are the general-purpose medium tolerance solution and then the use of Air Snaps allow for checking critical outside diameters, according to Schuetz.

Accuracy in the Tried and True

Technology upgrades in Mitutoyo’s extensive line of metrology hand tools means more accurate tools that are easier to use. “Our small hand tools continue to be the majority of our business,” said Pat Harkness, national sales manager for distributed products for Mitutoyo America (Aurora, IL), illustrating the utility of the devices. There is a need for more accuracy in simple tools. “As an example of higher accuracy, our new MDH hand-held micrometer measures to a 0.1 μm resolution.” Illustrating the art of the possible in hand-held devices, this device is now so sensitive that heat from an operator’s hand needs to be accounted for. Mitutoyo includes a heat shield, to minimize thermal expansion error of the frame when performing hand-held measurements.

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Mitutoyo’s MeasurLink software helps operators choose the right hand tool for measurements among the many available.

“It is surprising how many people today need to see that level of accuracy, that last digit if you will. We are selling these fairly well,” said Harkness. He observes a wide variety of applications of the MDH, from in-line production use to inside calibration laboratories. “I think in the future you’re going to see more and more of these advances into higher accuracy because specifications continue to get tighter,” he said. As production rates increase, so does the need to make faster measurements. Mitutoyo is responding with some simple solutions to that. He pointed out that, for example, their QuantuMike Series micrometers allow operators to move the thimble four times faster than other micrometers. “Someone who is doing a lot of inspection in a day may need to be a little bit quicker, and this helps him,” he remarked.

Wireless Data Transfer

Maintaining focus on speed, Mitutoyo also offer a wireless data transfer system for data to support SPC. “Our digital tools have an option for data transfer, using our U-Wave system with our own Digimatic protocol,” explained Harkness. Each receiver can transfer data from up to 100 gages from up to 70′ [21.3 m] away, making it ideal in larger shops for statistical process control. “This is a longer distance than from standard protocols like Bluetooth,” he said.

To make things even easier for shop-floor personnel, the company’s MeasurLink software reduces error by guiding shop personnel on which device to use and how to perform a measurement. The number of devices that could possibly make a measurement can be overwhelming, including calipers, micrometers, indicators, snap gages, bore gages, inside micrometers, depth gages and more. This presents operators with perhaps too many choices. Using a CAD model of the workpiece, a quality professional sets up a program that is easily read and interpreted, providing instructions on how to take measurements and which tool to use. “It will actually instruct the operator to grab certain tools, and it reduces a lot of error out in the field,” said Harkness.

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Some tools remain useful for many decades, such as this Mikrokater indicator supplied by A.A. Jansson—with proper care and treatment.

This is an important trend Mahr Federal is also responding to. “We are integrating wireless data transmission directly into our digital indicators and calipers to make it easier to collect data. We then employ a very inexpensive receiver to input the data right to the computer providing a wireless solution at virtually the same cost as a wired system,” said Schuetz from Mahr. This eliminates special cables or bulky add-on units for wireless transfer. Their MarConnect Integrated Wireless product is a plug-in device to a laptop that connects up to eight measuring devices for secure download or more simply by adding inexpensive receivers. Schuetz explained that it is not a Bluetooth system, but rather similar to technology to that used in wireless medical devices. “It provides secure and reliable data transfer and long battery life,” he said.

“We are seeing an increasing demand for this [wireless digital data transmission],” said Lee Kirtlink, senior channel marketing manager for the Tesa brand of Hexagon (North Kingstown, RI). “Right now, the technology is mostly being tested by those customers that like to try out exciting new products, so the percentage of customers using the technology is small.” However, he notes there is a great deal of interest in transmitting metrology data wirelessly. “It is clear that this technology will become mainstream very quickly,” he said.

According to Kirtlink, in 2012, Tesa introduced a new TWIN-CAL digital caliper which features wireless connectivity built into the tool. These calipers contain the technology necessary to add wireless data output simply by attaching the TLC-TWIN emitter/receiver. “This small cap can be attached in just seconds. This makes it easy, cost effective, and efficient to transmit measuring data in a practical way.” He also relates that tools with digital displays are the fastest growing trend in hand tools. “In addition to being easy to use, they are durable, accurate and reliable,” he said.

Extended Life and Tradeoffs

As technology in the higher end hand tools increases, so do concerns about miniaturization and especially battery life. “Hand-held electronics have to be very low power and use compact batteries even as they need to be more sophisticated to provide more features,” explained Jeff Wilkinson, general manager of the advanced technology division at L.S. Starrett. He is also director of research and development for precision hand tools. “Our customers will not tolerate a short battery life or a need to recharge constantly—just like with your cellphone.”

Wilkinson also stressed that advanced hand tools often offer a very cost-competitive solution for in-process measurement. “It takes time to set up a CMM for automated measurement, while quality professionals find you can often do more with a set of low-cost hand tools,” he said. Technology advancements can provide other advantages as well, perhaps using tiny embedded sensors that determine orientation or pressure on a measuring face to help consistency of use. Look for this in the future.

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Working with relevant, timely data is becoming ever more important, which is why Tesa brand from Hexagon thinks it is important to make wireless data transmission a practical, mainstream option in their tools.

Wilkinson believes technology advancements even in hand tools are important because of the evolution of the user market. Wilkinson was quick to point out that Starrett, like other providers, offers both electronic and mechanical devices. “Our vernier gages are accurate, rugged, and reliable, and they have no batteries that need replacing,” he said. “But the workforce is expecting to see digital readouts more and more. Companies are using these tools to support six sigma and other programs that need data, and moving that data electronically is also becoming more important,” he explained.

To help customers network measuring tools, Starrett offers its DataSure system for wireless data transfer. “Customers can connect right into their SPC applications or over a network,” said Wilkinson. “It is designed to be flexible in an industrial setting.” He stressed that these use a company proprietary, secure transfer protocol. The DataSure system features a separate end node that connects by cable to the output connector of a metrology device, as compared to other solutions that feature integrated wireless devices in the tool itself. Long battery life is a key concern to Wilkinson. “We use a separate battery in our DataSure units and we tailor the embedded radio to use extremely low power to the point where we can get five-million measurements out of one battery,” he said.

Dave Wood, technical director for Fowler High Precision (Newton, MA), also discussed the new availability of tools equipped with Bluetooth compatibility built directly into the unit. “This includes calipers, micrometers, indicators, bore gages, and inclinometers,” he explained. “There are a lot of people that collect data on these things, and having a wire connected to your instrument is a hindrance. So having a cable-free environment where you’re not worried about tripping over the cable and dragging the tool off the table is attractive,” he said. “We have had a good response from the market for these.”

He notes that using a commercial standard like Bluetooth allows them to communicate to portable devices such as today’s smartphones. “So somebody can walk around the floor and collect data without having to be tethered to a tool. That portability speeds things up because you can take the SPC process to the tool instead of bringing the data to the QC area or some central location,” he added.

Custom Made and Care

There is also a demand for custom hand tools, specialty devices for specialty uses. One of Fowler’s most popular are Fowler-Bowers three-point bore gages. “We do a lot of special applications with those where the anvils are custom-ground to fit a particular feature on the customer’s part,” he said. Relying on spring pressure to ensure consistent contact with the measuring surface means they are both fast and repeatable, according to Wood. Typically a user checks them against a master ring, which is often sold as a kit with the gage.

In the long run, it seems unlikely that there will be a truly high-tech replacement for these familiar devices in factories and on the shop floor. “It is really tough to replace metal-on-metal measuring,” remarked Wood, especially for bore gages, but the statement rings true for most of these devices. If treated properly, they can last for decades. “We get people all the time calling up [our repair department] looking for components or battery cover to some 25-year-old caliper that they’ve been using regularly ever since, and it’s finally just lost a part or given up on itself,” he said. The source of death of most gages is mistreatment, especially from new users. Keep it clean, keep it calibrated, find a consistent way to use it and reliable, simple measurements are yours.

This article was first published in the August 2015 edition of Manufacturing Engineering magazine.

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