How is the "total indicator runout" (TIR) measured?

• A. By evaluating the visual appeal of the part
• B. By rotating a part and measuring the total deviation from a true reference along its circular path
• C. By comparing against a theoretical model
• D. By measuring the perpendicularity of the part

Answer: (B)

Total Indicator Runout (TIR) is measured by rotating a part and assessing the total deviation from a true reference along its entire circular path. This measurement technique involves mounting the part securely and using a dial indicator. As the part is rotated, any variations in the surface position relative to a fixed base are recorded by the indicator. The highest and lowest readings during the rotation are used to determine the total indicator runout, reflecting how much the part deviates from its specified form or alignment.

This method effectively identifies imperfections, such as wobbling or misalignment, that may affect the functionality of the part in assembly or operation. TIR provides a comprehensive understanding of the part’s surface characteristics in a circular motion context, which is how many mechanical parts interact in real-world applications.