Chapter 11: Dimensional Measurement

1
Chapter 11 Dimensional Measurement

• Overview
• Classification of Measuring Devices
• Linear measurement and Gage blocks
• The use of micrometer and vernier caliper
• Optical method

2
Measuring Devices

• Low - Resolution devices (to 0.25mm)
• used directly or with of ,
  , surface
• Thickness gages
• Medium Resolution Devices (to 2.5 10-3 mm)
• used directly or with assistance of
  accessories telescoping gages, expandable ball
  gages
• instruments
• Specific-purpose gages or Measuring microscopes
• High- Resolution Devices ( to 2.5 10-5mm)
• used directly or with assistance of some
  mechanical comparators, electronic
  comparators, Pneumatic comparators, optical flats
  monochromatic light sources
• Super-Resolution devices various forms of
  used with special light sources

3
Linear Measurement Gage Blocks

• Accurate measurement of length with a
  standard gage blocks
• Gage block sets are industrys dimensional
  Classes of gage blocks for the SI system
• Accuracy Grade Accuracy (mm)
• 0.5 0.00003
• 1 0.00005
• 2 0.00010
• - 0.0005
• 3 0.00015
• - 0.0005
• Usage calibrate, setting special purpose gages,
  used with gaging devices
• Temperature problems ?L LCa?T

4
Example

• A steel ruler 30.48 cm long is used to measure a
  length of 20.32 cm. The ruler was manufactured in
  a controlled temperature environment of 25oC. At
  this reference temperature, the ruler has
  negligible bias error. Determine the design-stage
  the measurement error caused by thermal expansion
  in a reading of 20.32 cm. If the measurement is
  taken in a 37.8oC environment but not corrected
  for thermal expansion. Given the coefficient of
  thermal expansion of the steel is
  9.910-6in./in.oF
• (note oF 1.80C 32)

Solution ?L LCa?T 0.046mm.
5
Micrometer and Vernier Caliper
Micrometer
Vernier
6
How to Use Micrometer and Vernier
7
Optical Method

• Applications
• measurement of small dimensions using
  wavelength of light
• Measurement of by use of alignment telescopes
  with accessories and project systems
• Interferometer use of light
• Wavelengths of light of the various primary
  colors
• Wavelengths from specific sources

8
Optical Method