Dimensioning diameters

Marsh_138

Registered
Hello,

I have a doubt about dimensioning diameters,what is the correct way to measure a diameter (method,instrument,etc.) and where can i get that info,i hope you can help me ,thanks !!!

Miner

Forum Moderator
Do you have 2 questions here? It's not clear whether you have a question on how to dimension a diameter.

Regarding measurement of diameters, you need to consider the function of that diameter. Is it an OD or ID? What is the fit with the mating part?

Next, you need to consider what the measurement device is actually measuring. For example, a pin gage is measuring the smallest effective diameter of a hole. A CMM is measuring the average diameter, which will not necessarily clear a pin of the same diameter. A micrometer/caliper is measuring one of an infinite possible number of diameters. That diameter may be the minimum, the maximum, or any where in between.

Consider the process making that diameter. Will it produce lobes? How many? How will the gage handle that number of lobes?

Golfman25

Trusted Information Resource
Do you have 2 questions here? It's not clear whether you have a question on how to dimension a diameter.

Regarding measurement of diameters, you need to consider the function of that diameter. Is it an OD or ID? What is the fit with the mating part?

Next, you need to consider what the measurement device is actually measuring. For example, a pin gage is measuring the smallest effective diameter of a hole. A CMM is measuring the average diameter, which will not necessarily clear a pin of the same diameter. A micrometer/caliper is measuring one of an infinite possible number of diameters. That diameter may be the minimum, the maximum, or any where in between.

Consider the process making that diameter. Will it produce lobes? How many? How will the gage handle that number of lobes?

While 100% true, that's really funny. So little thought is put into dimensioning and measuring.