Quality Magazine - March 2009 - (Page 36) | QUA LIT Y M EA SU REM E N T | employing a tapered stem to further minimize deflection as well—and at the same time allowing for the stiffness to be near the probe unit and the stylus tip to be lighter and perform better. is generally the least expensive and most popular sphere material for a stylus, manufacturers must take into account the application and material being measured to determine the most appropriate ball material. “If the workpiece is hard, ceramic steel would be a better choice, as abrasive material can cause flats on the ball,” says Chrysee Bollon, styli and accessories business manager at Carl Zeiss IMT Corp. Too soft of a workpiece and build-up can occur on the ball, she adds. “Because of the risk of build-up, people go to another ball material such as ceramic. The properties of ceramic make it a better choice than the traditional ruby ball. Measuring hard materials creates a wear spot and soft materials create build-up on the ball,” Bollon says. For aluminum applications, many experts say that due to the transfer or build-up that ruby balls may endure, a material such as silicon nitride is a good fit. “The chemical composition of silicone nitride substantially reduces the accumulation of aluminum particles as compared to ruby, so the adhesive wear is far lower,” Schlafly notes. Bobo of Renishaw adds that a Zirconia ball is a good fit for cast iron applications. For glass applications, Horwell recommends diamond tip styli. Diamond styli tips were developed by engineers at Carl Zeiss. The material does not wear out with hard, rough materials and soft materials do not create build-up, according to Bollon. “It’s important to remember that the biggest factor for selecting the ball material is to choose the best fit for the specific application,” Dove recommends. Grade. Another factor to be aware of when choosing a ball for the stylus, is the grade of the sphere. The lower the grade number, the rounder the ball. For example, a grade 3 ball is rounder and considered superior to a grade 10. “Pay attention to the roundness of the ball. If you have a grade 5 vs. a grade 10, that would affect your point of measurement,” Bobo explains. Some suppliers only offer grades 3 and 5. However, grades 10 and above are available and, according to Clark, a grade 25 ball is just fine for most general shop jobs. “The only time the grade becomes really important is a highly accurate machine to reminds. “Larger systems and portable arms take larger thread sizes, allowing for more robust, non-magnetic and lightweight shank materials like titanium to be an ideal option in large ball diameters for less deflection, and more weight tolerance.” For applications that call for highly accurate results, experts recommend not only maximizing the styli by choosing a rigid material, but also 4 REASSESS ROUNDNESS. Material. When choosing the ball or sphere for the stylus, material, weight, mounting method and grade are all factors to consider. While ruby PARTNERING WITH INNOVATIVE BUSINESS LEADERS SINCE 1944 Original PI TAPE products, unequalled precision and durability DIAMETER MEASURING TAPES O-RING TAPES LINEAR TAPES CIRCUMFERENCE TAPES SPECIAL DESIGN TAPES Standard products are accurate to .001” Calibration report traceable to NIST furnished with all products CONTACT US FOR YOUR PRECISION MEASURING NEEDS PI TAPE CORPOR ATION www.pitape.com | Toll Free: 866.474.8273 | Direct: 760.746.9830 Quality Quick Clicks 413 at qualitymag.com 36 QUALITY | March 2009 www.qualitymag.com http://www.pitape.com http://www.qualitymag.com http://www.qualitymag.com
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