Podcast
Questions and Answers
What is the primary goal of indirect measurement?
What is the primary goal of indirect measurement?
What is the purpose of the polar chart in indirect measurement?
What is the purpose of the polar chart in indirect measurement?
How is the part centred on the revolving table?
How is the part centred on the revolving table?
What is the purpose of the transparent overlay chart?
What is the purpose of the transparent overlay chart?
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What is the issue with using vee-blocks to check for circularity?
What is the issue with using vee-blocks to check for circularity?
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What is the result of using the vee-block method to check for circularity?
What is the result of using the vee-block method to check for circularity?
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What is the purpose of the revolving table in indirect measurement?
What is the purpose of the revolving table in indirect measurement?
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What is the relationship between the part's surface and the indicator reading in the vee-block method?
What is the relationship between the part's surface and the indicator reading in the vee-block method?
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What is the advantage of using indirect measurement over direct measurement?
What is the advantage of using indirect measurement over direct measurement?
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What is the primary purpose of the radial and circular lines on the polar chart?
What is the primary purpose of the radial and circular lines on the polar chart?
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Study Notes
Geometrical Tolerances and Errors
- Geometrical tolerancing involves specifying the maximum permissible variation of form, profile, orientation, location, and runout of a feature.
- The tolerance value represents the width or diameter of the tolerance zone within which the point, line, or surface of the feature shall lie.
Straightness Tolerance and Error
- Straightness refers to a condition where an element of a surface or centerline is a straight line.
- A straightness tolerance specifies a tolerance zone within which the considered element of the surface or centerline must lie.
- Straightness tolerance can be applied to:
- Surface elements (e.g., lines, cylindrical surfaces, conical surfaces, flat surfaces)
- Controlling surface elements only (e.g., bending or wavy condition of the surface, but not the straightness of the centerline or conicity of the cylinder)
Circularity (Roundness) Tolerance and Error
- Circularity refers to a condition where all points on a circular line or the surface of a circular feature are the same distance from a common axis or center point.
- Errors of circularity can occur due to ovality, lobing, or random irregularities from a true circle.
- A circularity tolerance is measured radially and specifies the width between two circular rings for a particular cross section within which the circular line or the circumference of the feature shall lie.
- Circularity tolerance must be less than half the size tolerance since it controls surface elements only.
Assessing Circularity
- The circularity error is the minimum radial separation between two concentric circles within which all points on the measured surface shall lie.
- Measuring principle involves establishing the relationship of the perimeter of a feature with a perfectly round form, regardless of its size or the exact position of its center.
- Measurement can be done using a polar chart, where readings are entered and evaluated for circularity errors.
Measuring Principle
- The measurement of circularity presents some problems, as it does not lend itself to direct measurement.
- Indirect measurement involves establishing the relationship of the perimeter of a feature with a perfectly round form.
- Measurement can be done using a revolving table and a fixed indicator or by revolving the indicator around the part.
Alternative Measuring Procedures
- Alternative methods include checking parts for circularity by revolving them in suitable vee-blocks while measuring the upper surface with an indicator gage.
- When using this method, the full indicator reading is approximately equal to a measurement over a diameter instead of over a radius.
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Description
This quiz covers the concepts of geometrical tolerances and errors in engineering, including dimensions, geometry, and surface finish. It explains the importance of tolerancing in ensuring the proper function of products.
