A Hole’s Virtual Size
Answer the following questions based on the figure shown.
- What is the hole’s LMC 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 Least Material Condition (LMC) feature modifier. A LMC modifier describes a size condition in which the least amount of material exists within its dimensional tolerance. For a hole, LMC is the dimension that produces the largest cutout. Thus,
$$$LMC_{hole}=.190+.005=.195$$$
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 LMC:
- Outer Boundary (OB) = LMC (think largest hole) + geo tol = Virtual Size/Condition
For an External Feature (Pin) with Geo Tol at LMC:
- Inner Boundary (IB) = LMC (think smallest 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:
$$$.195+.014=.209$$$
In the feature control frame, the perpendicularity tolerance is the one associated with Datum A only. Thus, the hole’s virtual size is:
$$$.195+.006=.201$$$
- .195
- .209
- .201