This page will offer resources and information that will help you better understand the basic aspects of gaging and inspection tool device design. Here are a few of the subjects that will be covered on this page:
- Tolerances and Allowances
- Gage Tolerances
- Gage Types
- Magnifying/Amplifying Dimensions
Tolerances and Allowances
Because of the limits of manufacturing, all part dimensions are made within a specified working tolerance, which is the total permissible amount by which a dimension may vary from a specified size. When providing tolerances, designers recognize that no two workpieces, distances, or quantities can be exactly alike.
Gage tolerance is expressed as a percentage of workpiece tolerance. For fixed, limit-type working gages, gage tolerance is generally set at 10% of workpiece tolerance. The tolerance of inspection gages is usually 5% of work tolerance. Master gages, those used to check the accuracy of other gages, are usually 10% of gage tolerance.
A wide variety of gages are available to visually inspect and gage parts. A few of the basic types include:
- Screw-pitch gages
- Plug gages
- Ring gages
- Snap gages
As dimension changes become too small for easy measurement, it is necessary to amplify or magnify them prior to measurement. This can be performed mechanically, electronically, pneumatically, or optically using a variety of tools.
Dial indicators have a contact point that is attached to a spindle or rack. When this spindle or rack is moved, it transmits that movement to a pinion and then through a train of gears. These gears magnify the movement, which is then read off the hand on the dial face of the indicator. Because the principle of direct reading from a graduated dial face provides both accuracy and speed of reading, the dial indicator has been incorporated into many types of gaging equipment.