Keep in mind that it's possible to have certain combinations of pin diameter and bore diameter that are mutually tangent without visually filling the entire space of the bore. While it's unlikely to encounter this scenario during actual measuring use, it's still a valid application of the theorem and the calculator. So if you're seeing an odd result of this nature, verify in your CAD program of choice or pen and paper before submitting a bug report or request for help.

Diameter of boremeaning

Hole calc also has a "reverse mode" calculator. When you enter the diameters of two pin gages and a bore, the reverse calculator will output the diameter of the remaining, third pin which will fit into that bore diameter. This can be useful if you want to determine the best combination of available pin gages to measure a target bore diameter. As with the three pin calculator, it is possible to enter values that are mathematically impossible to calculate, in which case the calculator will show an error message.

This calculator simply does the math for you- it does not substitute for an understanding of the metrology involved in measuring holes. A full overview of how to use pin gages and measure holes is outside the scope of this guide (this video is a good starting point). However, the following caveats should be kept in mind when attempting to do precision work using the three-pin method:

Diameter of boremeasurement

This calculator is based on Descartes' Theorem, which states that for every four mutually tangent circles, the radii of the circles satisfy a certain quadratic equation. The circles described in this theorem are also known as Soddy circles. If we assume the three pins used for the calculator measurement all touch each other as well as the larger bore they fit into, finding the diameter of the bore is a straightforward application of the quadratic equation described in Descartes' theorem.

Hole calc provides a set of simple calculators to determine the diameter of a bore based on the size of three pin gages (a.k.a. plug gages or gauges) that fit into it. This three-gage method can provide a quick way to measure bore diameters when you don't have access to a GO/NOGO gage pair or other precision bore measuring method. Measurements obtained via the three-pin method should be considered approximate relative to the use of these other methods.