Ⓜ Maximum material boundary
Maximum material boundary · Anotaciones de plano · ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Gauge Ø = hole VC” states a maximum material boundary requirement.
What controls
A boundary that the feature may not violate on its maximum material side, resulting from combining the size at maximum material condition with the applicable geometric tolerance. It is the boundary that guarantees assembly: if no part violates it, the parts assemble. It is also the concept that sets the size of a functional gauge, and when it accompanies a datum letter in a feature control frame it defines the size of that datum feature simulator at its maximum material condition, allowing some shift between the part and the fixture.
How to verify
In production, a functional gauge made to that boundary: if the part goes on, it meets size and geometry simultaneously. In coordinate measurement, it is evaluated with the material modifier enabled, checking that the combination of actual size and geometric deviation does not violate the boundary. When the modifier accompanies a datum, the simulator representing that datum must also be built to that size and not adjusted to the part.
Common mistakes when interpreting it
- Confusing it with plain size at maximum material: the boundary also includes the geometric tolerance.
- Building the datum simulator adjusted to the part when the frame calls for maximum material, which requires a fixed size.
- Using a functional gauge to verify feature control frames that carry no material modifier, where it is not valid.
How to get it in the workshop / if it comes out of tolerance
It is the number that tells you what diameter to make the pin or plug of an inspection gauge. Understanding this boundary is what lets you decide quickly whether a part is acceptable: if the feature respects the maximum material boundary, it assembles, even if its individual size and position values look tight. It is also why it pays to drill holes toward the large end of their tolerance.
Parts rejected for position that nevertheless assemble fine: check whether the maximum material boundary was evaluated with its bonus or whether a criterion independent of size was applied. If a functional gauge rejects parts that the CMM accepts, review how the datum is established: that is where the two methods diverge the most. And if you are a few hundredths short on position, making the feature somewhat away from maximum material is usually the cheapest fix.
Alternative symbol:MMB
Related symbols
Other symbols in Plan annotations
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