From Handbook of Dimensional Measurement, Fourth Edition


The straight line represents the path of all linear dimensions. Considering the premise that the shortest distance between two points is along a straight line, that path is not necessarily present in a physical sense on the part being measured for size, but it must be incorporated in the length measuring instrument. Straightness, which is a fundamental concept of linear measurements, is also a functionally important condition of many engineering products. As an introduction to the discussion of straightness measurements, a survey of a few basic methods is made in Table 11-2.

Table 11-2: Examples of Methods for Inspecting Straightness 1





Straightness of a surface element determined by its parallelism to a straight edge of known accuracy

Straight edge and gage blocks

Unequal height of the supporting elements create a controlled deviation from true parallelism. Gage blocks are used to check whether the digressions from the parallel at intermediate points correspond to the calculated values.

The straightness of a surface element inspected by direct contact with a tool of calibrated straightness

Knife edge rule

A knife edge rule brought to bear against the surface element to be inspected will indicate by the presence and width of light gaps the lack of contact caused by deficient straightness.

Straightness of a shaft determined by rotation on fixed supports and measuring the runout of its surface

Bench centers or Vee-blocks and indicator stand

Using the part's axis (between centers) or its surface...

Copyright Industrial Press Inc. 2007 under license agreement with Books24x7

Products & Services
Form Gages and Form Gaging Systems
Form gages and form gaging systems are used to inspect parameters such as roundness, angularity, squareness, straightness, flatness, runout, taper and concentricity. 
Surface Metrology Equipment
Surface metrology equipment is used to measure the surface finish and/or geometry of engineering components. Surface texture and topology characteristics include surface roughness, contour, form, waviness, and defects.
Precision Shafting
Precision shafting provides the highest degree of overall accuracy, concentricity, straightness and surface perfection attainable in commercial practice.
Autocollimators are optical instruments that measure angular displacements and are used to align optical components and measure optical and mechanical deflections.
Air Bearings
Air bearings use a thin film of pressurized air to support a load. They do not generate friction.

Topics of Interest

THE MEASUREMENT OF FLATNESS Flatness represents the geometric concept of the plane, when applied to a solid surface where it becomes measurable by mechanical means, either directly or in combination...

10.1 General statement One of the biggest problems of form is concerned with one of its boundaries i.e. waviness. Waviness is difficult to deal with from a purely geometric standpoint. It is not a...

A few simple tips for maintaining accurate, reliable ball screws. Use centers for all measurements. But before using them, verify that center holes are clean and undamaged. Just check a ground...

There are many factors that affect the capabilities of a linear stage to position accurately in three-dimensional space. Abbe errors, straightness, flatness, pitch, roll, yaw, hysteresis, backlash,...

Ideal for Machine Tool users, the D640 will enable you to check straightness of machine axis, spindle direction, spindle to spindle / tail stock, squareness of machine axis, flatness of machine table,...