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4.6 Snap gages

D.M. Donner

Snap gages are relatively inexpensive tools which are used to measure the ID of parts. They are transfer devices which require the use of a micrometer to determine the final dimension.

A set of snap gages in a green plastic case.
Figure 4.96. A set of snap gages in a green plastic case. / Image Credit: Damon Donner, CC BY 4.0

Snap gages come in sets to measure various bore sizes. A bore is a cylindrical feature created to enlarge a drilled hole. Snaps gages are used to record the diameter of a hole and then transfer that recording to a direct reading tool such as an OD micrometer.

A progression of three photos showing the snap gage arms extended, retracted and locked in place with a thumb screw.
Figure 4.97. A progression of three photos showing the snap gage arms extended, retracted, and locked in place with a thumb screw. / Image Credit: Damon Donner, CC BY 4.0

Snap gages have two collapsible anvils, which can be locked in place by rotating a knob on the end of the handle.

A snap gage in a bore with the handle sloped down.
Figure 4.98. A snap gage in a bore with the handle sloped down. / Image Credit: Damon Donner, CC BY 4.0

To measure a bore, a snap gage is set with the anvils extended to a diameter larger than the bore. Then, the following steps are taken.

1. Collapse the anvils and place in the bore at an angle as pictured above.

2. Turn the lock. This applies pressure to the anvils, restricting their movement.

A snap gage in a bore with the handle sloped up.
Figure 4.99. A snap gage in a bore with the handle sloped up. / Image Credit: Damon Donner, CC BY 4.0

3.Swing the snap gage so that the arms compress as they pass through the bore diameter.

A snap gage between the anvil and spindle of an outside micrometer.
Figure 4.100. A snap gage between the anvil and spindle of an outside micrometer. / Image Credit: Damon Donner, CC BY 4.0

4.Take the snap gage to a micrometer and gently measure the length created by the anvils.

Attributions

  1. Figure 4.96: Snap gages used to measure bores by Damon Donner, for WA Open ProfTech, © SBCTC, CC BY 4.0
  2. Figure 4.97: Snap gage anvils and lock by Damon Donner, for WA Open ProfTech, © SBCTC, CC BY 4.0
  3. Figure 4.98: Install snap gage by Damon Donner, for WA Open ProfTech, © SBCTC, CC BY 4.0
  4. Figure 4.99: Swing snap gage by Damon Donner, for WA Open ProfTech, © SBCTC, CC BY 4.0
  5. Figure 4.100: Read the diameter on a micrometer by Damon Donner, for WA Open ProfTech, © SBCTC, CC BY 4.0

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Introduction to Machining Copyright © by SBCTC is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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