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Getting the Fixturing Just Right
A gage requires just enough fixturing to do its job accurately and cost-effectively. Since the fixture establishes the relationship between the workpiece and the measuring system, its design and manufacture is as important to accurate gaging as the measuring instrument itself. However, in addition to accuracy issues, the fixture design can make a difference in a gage’s efficiency and economy of use.
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Measuring Surface Finish on Valve Seats
Measuring surface roughness of valve seats on cylinder heads is challenging. The land areas are short, and the roughness values are high. Normally, valve seats require basic roughness parameter analysis by a skidded measuring system. However, because of the short length and high roughness values, some argue that a skidless system is the best way to measure roughness of these surfaces.
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The Digital Caliper as a Swiss Army Knife
Sometimes a tool that provides suitable performance in a variety of applications is a better choice than a tool that performs extremely well at one dedicated job.
Read MoreGiving Your Gage More Intelligence for Less
Years ago, I wrote a column in this space that talked about how electronic gaging amplifiers could help make gaging more efficient and productive. Like phones and computers, today’s bench amplifiers offer greatly improved performance, better displays, less power consumption and more data user capabilities.
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The “C” in Gage and Other Components
Gages and measuring instruments come in all different shapes and sizes.
Read MoreDial Vs Digital Indicators
In the 1980s, digital electric indicators were expected to blow mechanical dial indicators out of the water. Despite electronic indicators’ higher resolutions, better accuracy and usefulness in statistical process control and data collection systems, mechanical indicators retained other advantages and continued to be specified by many users.
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Functional and Free
When gaging with mechanical or electronic transducers, you can sometimes get more than you bargained for in terms of the results from the gage.
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Making a Budget and Sticking to It
We have talked about the gaging process and evaluated it through various testing methods such as GR&R studies. We have also seen that there are other factors that influence gage performance, such as linearity, long-term stability and bias from the gage design. Combined, measuring-system-based factors that influence results are called the “measuring uncertainty.”
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What Do You Mean by Accuracy? (20 Years Later)
Nearly twenty years ago, I wrote the column “What Do You Mean by Accuracy?” Since then, new standards have been created or updated to reflect new developments and thinking about what accuracy is. So, has accuracy changed?
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Checking the Performance of Surface Finish Gages
The measurement of surface finish has come a long way in the past 60 years. We have advanced from fingernail scratch pads to microprocessor- and PC-based systems with inductive probes. We even have the choice of optical sensors to evaluate part surfaces.
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Gage Repeatability and Reproducibility Studies
GR&R studies are a way to assess the reliability of gaging results. For these studies, a few gage operators measure a small number of parts, several times each. The results are compiled and reduced to a single number that indicates the total expected spread of measurements for a single part, for all trials, by all operators. This number is expressed as a percentage of the total part tolerance.
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GR&R Studies: Measuring the Measurement
Over the last few columns we’ve been talking about measurement system analysis, or MSA. A key component of this overall analytical process is the GR&R study, officially known as ANOVA GR&R, or “Analysis of Variance Gage Repeatability and Reproducibility.”
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