Measuring Threaded Holes

Overview

This article gives a brief description of how to use a FaroArm^® to properly measure the position of a threaded hole.

Setup

The FaroArm should be mounted on a tripod or fixed in a manner that prevents any movement throughout the measurement process.

Be sure that part does not move significantly while in the process of taking measurements.

Process

1. The FaroArm can be used to measure threaded holes/bores to define positioning of the hole only. If you are attempting to measure the major and minor diameters of a threaded hole, you will need to use a thread gage. If at all possible, it is recommended that you measure holes prior to tapping threads.
2. Because the diameter of the hole does not affect the center point of the corresponding circle or cylinder, we can measure the circle/cylinder on the threads.
3. Assuming the threads are cut at the same height around the entire hole, we can reference points on the threads at various locations around the hole.
4. Make sure that the probe is seated between two threads. Basically, the threads are used to constrain the ball from sliding up and down the walls of the hole.
   
5. The hole can be measured as a circle or a cylinder, the important aspect is to be sure that the ball is seated between threads each time a point is taken.

Note: you may have to experiment with different ball probes to find one that seats in your particular threads consistently.