MMC Hole’s Virtual Size
Answer the following questions based on the figure shown.
- What is the hole’s MMC size?
- What is the hole’s Virtual Size relative to Datums ABC?
- What is the hole’s Virtual Size relative to Datum A?
Hint
Breaking down the parts of a feature control frame:
Hint 2
The virtual condition is used to analyze the clearance distance between mating parts. It is a constant boundary generated by a combination of a feature of size’s specified MMC or LMC and the geometric tolerance for that material condition.
Breaking down the parts of a feature control frame:
The problem statement specifies a Max Material Condition (MMC) feature modifier. A MMC modifier is the condition in which a feature of size contains the maximum amount of material within the stated limits of size. For a hole, MMC is the dimension that produces the smallest cutout. Thus,
$$$MMC_{hole}=.180$$$
The virtual condition is used to analyze the clearance distance between mating parts. It is a constant boundary generated by a combination of a feature of size’s specified MMC or LMC and the geometric tolerance for that material condition. In summary,
For an Internal Feature (Hole) with Geo Tol at MMC:
- Inner Boundary (IB) = MMC (think smallest hole) - geo tol = Virtual Size/Condition
For an External Feature (Pin) with Geo Tol at MMC:
- Outer Boundary (OB) = MMC (think largest pin) + geo tol = Virtual Size/Condition
where
$$geo\:tol$$
is the stated value in the feature control frame.
In the feature control frame, the positional tolerance is the one associated with Datums ABC. Thus, the hole’s virtual size is:
$$$.180-.012=.168$$$
In the feature control frame, the perpendicularity tolerance is the one associated with Datum A only. Thus, the hole’s virtual size is:
$$$.180-.005=.175$$$
- .180
- .168
- .175