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What is “TIR”

TIR stands for total indicator runout. TIR can also be known as full indicator movement or FIM. TIR is defined as the difference in measurement between the minimum and maximum measurement readings. This deviation is the variance from concentricity, cylindricity, roundness, or flatness. The total part that is included in TIR concerns the inclusion of all differences within the measurement as opposed to the difference that may exist on one side or one part of an object. Round, flat, and contoured features on an object are all included within the definition of TIR. TIR is measured by first setting up a particular part such that the part rotates around an axis. Then, using a dial indicator measured the surface of interest, collecting a maximum reading and a minimum reading. The difference between these two readings is calculated, with the resulting value equaling the TIR.

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