Quality Magazine - March 2009 - (Page 33) Operators should be well versed in their application before buying a stylus. Source: Hexagon Metrology Inc. Stylus Designs and Materials “What exactly do I need to measure? How accurate do I need to get? How deep do I need to go into the feature?” The answers will depend on the application and will help determine the type of styli to consider. In addition, say experts, operators need to read the manuals and parameters for their probe heads. Each piece of equipment has weight requirements and other stipulations that will guide the operator in the right direction in terms of what will and won’t work for the equipment. STAINLESS STEEL • Single-piece shank construction • Reasonably lightweight for lowforce applications • EWL relatively short in order to maintain stylus stiffness • Used primarily on tips ≥1 millimeter CERAMIC • Very stiff • Brittle (offering collision protection) • Lightweight • Used in medium length and diameter styli • Minimum stem diameter 2.5 millimeters Temperature changes can cause differences in measurements—making the choice of stylus material an important decision particularly if the application’s environment is not temperature regulated. “If your equipment is in a nonenvironmentally controlled area like a shop floor and you calibrate in the morning when it’s cool and use it later in the day, your measurements will be affected,” says Clint Clark of Q-Mark Manufacturing Inc. (Mission Viejo, CA). Changes in measurements may be minimal, but if the application’s tolerances are tight, such changes could make all the difference. When it comes to thermal stability in styli, ceramic stems are relatively unaffected by temperature changes and carbon fiber stems also are extremely thermally stable, Clark says. Manufacturer Carl Zeiss IMT Corp. (Maple Grove, MN) offers a stylus stem 2 TAKE THE TEMPERATURE. TUNGSTEN CARBIDE • Very stiff • Can be brittle (offering collision protection) • Very small diameters possible • Very heavy, limiting maximum reach and stem diameter • Used primarily on tips ≤1 millimeter Source: Renishaw CARBON FIBER • Very lightweight, most suited to strain gage probes • Good stiffness, suitable for long reach applications • Suitable for extension lengths, due to low weight • Extremely low thermal coefficient of expansion line called Thermofit, designed specifically for environments where temperature stability is a challenge. The line of styli is built to maximize both rigidity and thermal stability. For applications where temperature is unstable, factoring in thermal stability of the styli material is imperative to completing the measurement application. “In the olden days—if we went back 10 years—everyone said that styli 3 CHOOSE THE STEM WISELY. shouldn’t be longer than say 50 millimeters long and if went go longer, you’d have issues,” recalls Jonathan Dove, regional applications manager at Hexagon Metrology Inc. While experts agree to the general rule that the shorter and thicker the stem or shank, the better due to less deflection and more accurate measurements—the advancements in technology including better sensors and more evolved materials have made it possible for manufacturers to use longer, thinner probes for certain applications. Diamond tip styli do not wear out with hard, rough materials and soft materials don’t create buildup—making it a fitting alternative for many applications, including glass. Source: Carl Zeiss IMT Corp. A plastic automotive part held on a fixture is measured with an M2 ruby ball stylus with a carbon fiber shank. Source: Paul W. Marino Gages Disk styli are ideal for applications with undercuts or large diameters. Source: Q-Mark Manufacturing Inc. www.qualitymag.com March 2009 | QUALITY 33 http://www.qualitymag.com
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