How do you measure a non-feature of size 1

[MartinSr00]

I've read through both the ASME Y14.5M-1994 and Y14.5-2009 standards. They are very clear about how to measure features of size. For example: The minimum dimension on an external feature of size is the unrelated actual mating envelope. The maximum is the largest local size. Clear enough.

But what of measurements that are not features of size. For example, the length of a step in a shaft, where the surfaces to be measured are unopposed.

Look at the attached drawing. What is the min and max dimension for Dimension "A"?

 

[MartinSr00]

Yes -- Sorry, it's Rule #1.

As noted the 1.00 dimension is a feature of size.

The original question was about dimension "A". That's not a feature of size.

 

[fsincox]

Sorry, I see dimension "A" now, I apologize for that. Remember, The ANSI standard warns that drawings may not be complete drawings (1.1.4 Figures) and neither is your example.
Determination of real world conditions requires real world parts/drawings. There will be a dimension of size, most likely the overall size/width/heitht or the "A" dimension that will also come into play. Then you would be able to do some calculation like you are asking for.
People always bring a drawing and ask: "how shall I dimension this", and I will say "what does it do" we must see the assembly/function to know how to do it.
You just can't decide these things with partial information.

 

[MartinSr00]

fsincox

When I must make a drawing special sized hex bolt, and wish to dimension it functionally along it's axis, I dimension the thickness of the head (a feature of size) and the length (not a feature of size). I've always judged that the drawing is not an instruction sheet for the machinist, rather a specification of a part that is dimensioned in accord with its function.

True, others may make their judgments differently. Old style machinists will complain because they don't want to take out a calculator and then manage their tolerances on each side of the washer face.

If the hex bolt is in a blind hole, and there's so much clearance in the assembled state above the nut face, it makes perfect sense to dimension the bolt with this in mind. The bolt head thickness may allow a very large tolerance. The length a small one. With an overall, you're over-tolerizing the head thickness to keep the length in order and ultimately could reject perfectly functional parts.

This example was posed for situations like this.