I've been doing some GD&T training lately and one thing that seems to complicate things for me is Rule #1 (aka the Envelope Principal). It states that at MMC, a feature must have perfect form and as it departs from MMC, a form error is allowed in the amount equal to the deviation from MMC. Unless there is a form callout that further refines and limits it. Say I have to add a flatness dimension for Datum A as shown below. The flatness comes in at 0.08, which is within tolerance. BUT there are at least 6 other features on this part that are dimensioned to Datum A. If the 23 +/- 0.5 for example measures at 23.45, that only allows me a form deviation of 0.05. The flatness is now out of tolerance. But how do I get PC DMIS to account for that? The flatness is still going to report in tolerance at 0.08, even though Rule #1 has now been violated. Worse yet, (and this is just rhetorical) how do I tell the shop supervisor that I have to reject his parts even though the flatness is reporting in tolerance when it's actually not?
As has been stated, that's not a feature of size. It's 2 separate features. To be a feature of size it needs to be a width, with an inline dimension that connects each side and a size tolerance.
Your drawing is a linear dimension. Linear dimensions are normally checked by measuring the unrelated actual mating envelope (UAME), which in this case would be tangential planes that contact the 3 highest points of each plane, unconstrained to each other. Similar to putting one plane on a surface plate and measuring the highest points on the opposing plane to get a distance.
As has been stated, that's not a feature of size. It's 2 separate features. To be a feature of size it needs to be a width, with an inline dimension that connects each side and a size tolerance.
Your drawing is a linear dimension. Linear dimensions are normally checked by measuring the unrelated actual mating envelope (UAME), which in this case would be tangential planes that contact the 3 highest points of each plane, unconstrained to each other. Similar to putting one plane on a surface plate and measuring the highest points on the opposing plane to get a distance.
