ANSI Y14.5 1982 - Rule #1 - envelope ??

[Tmoose]

We have copies of astm y14.5 for the last 20 plus years.

Some of our older title blocks reference ANSI Y14.5 1982.
I'm pretty sure that back in the days of yesteryear (ANSI) Rile #1 enveloper was valid.
The specific question is if a hole with a toleranced diameter requires perfect form at MMC, so an inscribed cylinder/"oerfect" shaft would fit inside, like it does today.

It would be most helpful, if somebody has that standard, they check and confirm or deny .
An informational screenshot of that section would make a nice addition to our arsenal that we hope we do not have to unleash on a current supplier "situation."

thanks,

Dan T

 

[ewh]

My copy of Y14.5M-1982 has no mention of Perfect Form in the Fundamental Rules 1.4 (a thru k).
Sorry.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[3DDave]

It should be in there somewhere - my copy of "A Treatise on Geometrical and Positional Dimensioning and Tolerancing" by Lowell W. Foster in 1963 says "When no tolerance of form is specified" "No portion of an individual feature shall cross the boundary of perfect form at MMC." It's unlikely to have been forgotten by 1982.

 

[ewh]

It is mentioned further in the standard, but it is not mentioned in the Fundamental Rules.
I think that para 2.7.1.2(a) is what the OP is looking for.

2.7.1.2 Variations of Form (Envelope Principal)(a) The surface or surfaces of a feature shall not extend beyond a boundary (envelope) of perfect form at MMC.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[sendithard]

If a part drawing calls out a recent ASME 14.5 does a typical plus minus length tolerance need to abide by the envelope rule? Also, I was wondering since such a dimension and tol doesn't have a fcf and a drf should it be measured against a datum if there is one representing an x zero location or do you mic in several places not using a surface plate datum so to speak?

 

[Belanger]

...does a typical plus minus length tolerance need to abide by the envelope rule?

That's a loaded question It gets into specific terminology: If the length you're speaking of is a "regular feature of size" then yes, the envelope rule applies (if it's not non-rigid, and if it doesn't have a circled I).

For the second part of your post: No, only qualities that are toleranced with a FCF should be measured from the datum(s) referenced in that FCF. For non-GD&T dimensions, the designer might need to indicate a "dimension origin" symbol.
For the final thing you mentioned: Using calipers or mic will tell you the "actual local size," which is only part of the story when measuring size. The envelope rule might then kick in, which means you'd have to also verify the "actual mating envelope" of the part with some sort of go gage.

 

[3DDave]

"Size" is checked independently of a feature control frame or any datum feature references.

 

[sendithard]

So if a part only uses a GDT fcf for a hole TP utilizing the typical ABC datums, yet the length is a simple 3.000 +-.005 Is it simply appropriate to just mic the corners and the center and if all are good we are good. A closer look shows a concave left side and convex right side so mic inspection passes but the surface plate/datum like representation on length would fail using a dial indicator. I'm confused which would be correct and/or if it needs to be specified for no ambiguity.

 

[Burunduk]

sendithard,
The 3.000 +-.005 toleranced dimension is only unambiguous to control distances between opposed points across widths of tabs/slots or diameters of cylinders. If the intent is to control location, profile (for surfaces) or position (for features of size) with datum references is the proper practice.