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NEWS FOR IMMEDIATE RELEASE

Mahr Federal Inc.
Gary Robison
1144 Eddy Street
Providence RI 02905 USA
(401) 784-3275

Media Contact:
THOMAS RANKIN ASSOCIATES
Tom Rankin, APR
401-884-4090
tomr@trankin.com

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Air Gaging the Choice for Measuring Taper in Orthopedic Device Manufacturing

-- Provides fast, easy, high precision results even under the toughest shop conditions

PROVIDENCE, RI -- Tapers play an important role in orthopedic devices. Most hip and knee implants use tapers because they provide good alignment and can be "locked" into position. In manufacturing these devices, the control of taper and size determines how well the implants perform over their lifetime. Increasingly, air gaging has become the inspection tool of choice for controlling these critical parameters.

"Air gaging was the breakthrough gaging technology of the '40s and '50s" said George Schuetz, Director of Precision Gages for Mahr Federal. "Introduced decades before electronic gaging, it provided the first high performance—50µ" or better—gaging on the shop floor. Despite its age, air gaging today is actually growing in popularity, especially in high precision areas like orthopedic devices. It is fast, easy to use, provides high precision results even under the toughest shop conditions, and can last for years measuring literally millions of parts."

For years the taper design of choice for orthopedic devices was the simple round taper, Schuetz said. It functioned well, but with demands for better performance, new designs have been developed. Innovations such as special surface finishes and complex taper forms employing oblong tapers have improved orthopedic device performance.

But all these tapers offer unique challenges to gage designers. "The problem is not just measuring taper or diameter," said Schuetz, "but measuring these dimensions on parts that may be only 12mm in diameter and 12mm in length. Even on parts that are longer, more points frequently need to be measured and more data collected."

Air gaging uses orifices that are 0.050" or smaller. They can be placed within 0.10" of each other and combined to produce any number of dimensional and geometric results. "Small electronic sensors or eddy current type sensors may approach the size of an air jet," said Schuetz, "but nothing can match air's economy or ability to work in a wet and oily shop environment right at the point of manufacture."

Air gaging uses the principle of back pressure to determine the size of a measured part, Schuetz explained. It is typically used for applications like precision medical tapers, where tolerance is fairly tight—usually less than +/-0.001"—and surface roughness is less than 50µ" Ra.

Medical implants take a beating and the taper fit between the female and male components is critical. The two pieces have to lock together and sit at the correct height. During manufacture it is common to inspect 100% of parts to ensure the accuracy of both components, and air gaging offers three ways to do this.

The most common type of air gage taper tooling has two pairs of jets on opposing air circuits, and is designed for a "jam fit" between the part and the tool. If the taper angle is incorrect, there will be excessive clearance between the two surfaces at one or the other end of the taper. Either situation can reduce the rigidity of the connection, which over time can cause the lock to fail. If the taper angle is correct but the size is incorrect, then the overall length of the orthopedic assembly will be incorrect and provide unexpected results after implant.

Jam-fit tooling does not measure part diameters, per se. Rather, it displays the diametrical difference at two points on the workpiece, as compared to the same two points on the master. To learn more about the taper components' positioning accuracy, you need a "clearance" style air tool in which an air taper ring cavity is sized to accept the entire taper part. Depending on where the part's reference surface is, the part can be referenced on the end of the taper or on a flange against the top surface of the part. This makes it possible to measure diameters at known heights. An additional set of jets may be added, to inspect for bell-mouth and barrel-shape, two more conditions that reduce the contact area between the male and female components.

The third type of air taper gage is a cross between the styles mentioned above. This is called a "simultaneous fit" taper gage. It is basically a jam-fit air tool with an indicator that references on the face of the datum surface. This indicates how far the air tool goes into the part being measured. So while the air gage provides a reading of the taper angle, the indicator provides an indication of the size of the diameters.

"But the best part about air gaging is that it's easy," said Schuetz. "The pressurized air from the gage tends to clean the part as it's being measured, and production workers do not require special training to use air gages. To check a hole, for instance, it is not necessary to develop skill in "rocking the gage." To find the true diameter, merely insert the air plug in the hole and read the meter. It is as simple as that."

MFIinfo

Mahr Federal Inc., a member of the Mahr Group, has over 150 years of experience providing dimensional measurement solutions to fit customer application needs. The company manufactures and markets a wide variety of dimensional metrology equipment, from simple and easy-to-use handheld gages to technically advanced measurement systems for form, contour, surface finish and length. Mahr Federal is also well known as a producer of custom-designed gages and a provider of calibration and contract measurement services. Mahr Federal's calibration laboratories are accredited to ISO/IEC 17025:2005 NVLAP Lab Code 200605-0 (see our Scope of Accreditation for accredited calibration processes). For more information visit www.mahrexactly.com

For additional information, contact:
Marketing
Mahr Federal Inc.
1144 Eddy Street
Providence, RI 02905 USA
Tel: (800) 343-2050 or (401) 784-3100
Email: mkt.nafta@mahr.com
Website: www.mahrexactly.com

Photo Captions

<< Dome_Jets_b.jpg >>
A great feature with air tooling is the ability to get numerous jets in a tight location. An additional set of jets may be added to inspect for bell-mouth and barrel-shape, two more conditions that reduce the contact area between the mating components.

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Since air tooling is custom made per the application, it is simple to use with virtually no operator influence and very low GR&Rs.

<< HipSocketComponents.jpg >>
All these components have a critical taper. Whether the part is metal or some synthetic compound, air gaging can verify size and taper.

<< Tool_Insertion_7246b.jpg >>
No other inspection system can live and work as close to the point of manufacture for tapered parts as air gaging, and provide immediate results.

ref: MFI8486.0509


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