When you don't have a gage pin big enough...

WesEDM's picture
Average Bloke
When you don't have a gage pin big enough...


As an example, let us say I have a hole that is 1.250" in dia. but I don't have a gage pin that big. Can I use two smaller gage pins to check the dia. reliably? I've heard many people say that this method works but I have my doubts.  Would anyone recommend this method? I've seen a college paper on using 3 pins but nothing reliable on using just two.

Chris G.
MSC Metalworking Tech.

Hello WesEDM,

     There is no published information for using just 2 pins and you've seen the articles for using 3 pins. The 3 pin method seems to be the most accurate way to measure in a situation like this. That is not to say that a 2 pin method would not work, however, there are a few things to consider when using 2 pins. For instance, it may be more difficult to ensure that the pins are sitting perpindicular to the machined hole. It will also be difficult to ensure you are sitting in the hole at "top center" of every radius involved in the measurement, using 3 pins eliminates that problem. The 2 pin method could work for you but it will take extra time to be sure your measurement is accurate. Don't forget to take into account the tolerencing of both pins together during the measurement. 


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