⌖ dim Toleranced dimension with GD&T
Toleranced dimension with GD&T · Anotaciones de plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “⌀10 H7 + ⌖ ⌀0.05 |A|B|C|” states a toleranced dimension with gd&t requirement with a cylindrical tolerance zone of ⌀ 10 mm, measured from datums A, B, C in that order of precedence.
What controls
A very common situation in which the same feature is governed both by a size dimension with its tolerance and by a geometric feature control frame. They are two independent requirements that are met or failed separately: size limits how much material there is, and the feature control frame limits where the feature is and what form it has. They are only linked when a modifier ties them together, such as the envelope requirement or a material condition modifier.
How to verify
Two separate checks: size with a two-point instrument or limit gauge, and geometry by CMM relative to the drawing's datum reference frame. If there is a material condition modifier, the actual measured size feeds into the bonus tolerance calculation, so the two measurements interact. The report must record both results separately, because they are independent characteristics.
Common mistakes when interpreting it
- Accepting the feature after checking only the diameter.
- Assuming size and geometry are always linked: they are only linked when a modifier ties them together.
- Correcting the machining program without knowing which of the two requirements was failing.
How to get it in the workshop / if it comes out of tolerance
During inspection, never accept a feature because it meets only one of the two: a hole can be perfect in diameter and out of position, or perfectly located and out of diameter tolerance. And in manufacturing, keep in mind that the two requirements are achieved with different levers: size with the tool and its offset, location with the work offset, workholding and rigidity.
Feature rejected: first identify which of the two requirements failed, because the correction is completely different. If size fails, look at the tool, wear and offset. If geometry fails, look at the work offset, clamping and rigidity. And if there is a material condition modifier, check the bonus before rejecting: with the actual size in hand, a part that appears out of position may be acceptable.
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