MEASUREMENT & INSPECTION
toward customers asking for the CMM-types of metrology devices that his company provides, equipped with either touch trigger or scanning analog probes. In particular, smaller CMMs are becoming a popular choice for such applications. One example is Helmel’s Micro- gage with an 8 × 12 × 8" (203 × 305 × 203 mm) measuring range, equipped with a touch trigger probe for a total system accuracy of 2.9 + L/1000 µm (to the ISO 10360.2 standard). “High-volume production tends to be with smaller parts, which makes the smaller CMMs especially appropriate,” Whistler said. “Everyone in this business has seen a 1 × 1.5- m CMM in a facility measuring a lipstick case…it can often
Whistler also cautions that the environments such sys-
The G25 gaging probe from Marposs offers contact scanning for pre- and postprocess cycles on gear grinders and machining centers.
be wasteful.” Another key consideration is real estate on the shop fl oor, which is highly valued and often at a premium. A CMM with a small footprint—tailored for the size of the parts—is a logical choice.
“In many cases, the small CMM is viewed as a cost- savings over the custom-built hard gage,” he said. However, he stressed that it is premature to rule out the hard gage as a category. Air gages, LVDT fi xtures, bore sweeps, doghouse gages, and hand tools still offer value in shop-fl oor production. “Where a mini or micro-CMM becomes attractive is instances where the setting masters used with hard gages are expen- sive,” he said.
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tems are used in effectively are harsh in comparison to the controlled labs CMMs were fi rst used in. “To accommodate that, we think you need mechanical bearings instead of air bearings on such CMMs,” he said. While air bearings can be more accurate, he said, they actually fl oat on air and control- ling their motion in environments with vibration and distur- bances can be problematic. “Mechanical bearings are more rigid and can absorb higher accelerations and decelerations.” Additionally ways, motors, and scales need to be shielded and protected from metal dust that can “really beat up a machine” as Whistler describes it. Illustrating the trend, other such CMMs and equipment with smaller footprints include the Duramax from Zeiss, the Smart CMM from Wenzel, the Hexagon/ Brown & Sharpe Shop Floor 4.5.4SF, or the Equator fl exible gage from Renishaw. “These all have mechanical bearings,” Whistler said. Another interesting device on the small end is the zCat portable CMM from Fowler High Precision (Newton, MA). Its working volume is 27.5 × 27.4 × 9.8" (700 × 700 × 250 mm), with a machine dimension of only 16.5 × 6.7 × 24.5" (420 × 172 × 620 mm). It weighs only 30 lb (13.7 kg) and features a convenient carrying handle at the top. The machine is outfi tted with its own Fowler zCat touch trigger probe. Linear accuracy is speci- fi ed as (4 + D/100 mm) µm, diametral accuracy as (2.0 + D/100 mm) µm, both to 1σ. It requires a fi xturing accuracy
requirement of 5 mm. “Because the concept is so new, there is not an international standard to reference for accuracy,” said Jeff Petersen, vice president of marketing and sales for Fowler. This mirrors some of the same issues with laser sen- sors and white light systems.
“Many of our customers envision using it to check parts next to machine tools or CNC milling machines,” he said. “We can train any operator to use the zCat.” Because of its small size, he also sees customers using it to measure parts that are still fi xtured inside larger machine tools. The ad- vantage in that scenario is not having to re-fi xture the part if more machining is required.
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