True Position Process Capability - A Better Method

On LinkedIn, I wrote a long article about a little known and better method to determine the process capability of a feature with a circular true position tolerance. Here is a link to the article that explains it in great detail.

Below is a table from that article that summarizes the method. The right side details what to do for circular true position tolerances. Compare it to the left side which is the method of finding process capability for standard dimensions explained in a different way to show the two methods are basically the same.

Here is link to a another blog post discussing some of the alternate methods and why they are not as good. I am starting to work on a technical paper on this same topic, so with a little luck, by next year I will be published. That would be pretty cool.

(added 12/2024)

There is an easier way to find the standard deviation. First, find the standard deviation of both the x and y components. Then take the square root of the sum of the squares, as if you were finding the "hypotenuse" of the x and y "legs". After I discovered this simplification, I found someone doing the same thing and called it the principal standard deviation. I can live with that name.