True Position Tolerance Zones- 2: Tolerance Zone Inspection
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.

We'll now use a plug gage to inspect the machined part from the previous page.

Assume that the plug gage will register off of the left face and bottom face of the part so as to gage to the surfaces called out in the print. It must be assumed that that the center of the gage pin is exactly 1.000 inch from the left and 1.000 from the bottom (go back and review the blueprint if you need to). Also the diameter of the gage pin will be exactly .020 smaller than the hole (.230) so that it can compensate for the tolerance zone.(blue)

The use of a gage plug works well for demonstrating screw and dowel clearances in later topics. But for now just remember that if the machined part fits over the gage without interference from the sides of the hole then it tells us that the center of the hole is within the tolerance zone.

From the above animation you can see that the gage pin acts to certify that the center of the hole is no more than .010 left, .010 right, .010 up, or .010 down from perfect center.
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label: true position, geometric tolerancing, ansi y14.5, tolernce zones