# Thread: Proper way to dimension diameter of cylinder

1. ## Proper way to dimension diameter of cylinder

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I am struggling with the proper way to dimension the diameter of a cylinder.
The thing that I am most concerned about is that the maximum circumscribed diameter is no larger than 4.5mm.

The issue that we have had in the past is that we specified a diameter tolerance of 4.5mm +.00/-.125 but, we ended up with a "TRI lobe" shape where the circumscribed diameter was measuring 4.6mm and wouldn't fit in the hole.

I cant decide if I give a diameter tolerance of 4.38 mm +/-.062 and a circular tolerance of .06mm.

2. What dimensioning and tolerancing standard are you specifying the drawing too? Ever heard of rule #1 (Envelope Principle) for ASME Y14.5?

Additionally, what is the size specification for the mating part?

3. Yes, I am dimensioning to Y14.5. The mating part has a tolerance of 4.51mm +.125/-.000.
I understand the Envelope Principle but, I am trying to figure out a way to specify the tolerance we need in GD&T terms.
Maybe I am over thinking it.
The past problem can not be detected using a standard two point measuring system, i.e. Micrometer or calipers.

4. Originally Posted by clint_clark
Yes, I am dimensioning to Y14.5. The mating part has a tolerance of 4.51mm +.125/-.000.
I understand the Envelope Principle but, I am trying to figure out a way to specify the tolerance we need in GD&T terms.
Maybe I am over thinking it.
The past problem can not be detected using a standard two point measuring system, i.e. Micrometer or calipers.
The envelope principle (Rule #1) is invoked by default when ANSI or ASME Y14.5 is declared on the engineering drawing. Rule #1 and limit tolerances are very much GD&T specifications. GD&T is not just the geometric characteristics (flatness, perpendicularity, etc..). The idea that limit tolerances are not GD&T (+/-) is an incorrect assumption.

Manufacturing and quality should be building the hole and mating pin such that the requirements of Rule #1 (3D boundary of perfect perfect at MMC).

You likely have both a manufacturing and quality problem..

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