GlossaryKind of term: Manufacturing termFeature control frame
What is a feature control frame?
A feature control frame is the rectangular box on a drawing that holds the symbol, tolerance value, any modifiers and the datums of one geometric requirement.
A feature control frame is the indication a drawing uses to state a geometric tolerance. You read it left to right: first the symbol of the characteristic, such as flatness, perpendicularity or position; then the tolerance value, with ⌀ in front when the zone is cylindrical or circular, S⌀ for a spherical zone, and any modifiers after it, such as Ⓜ; then the datums, each in its own compartment, in order of precedence. A leader line connects the frame to the feature the requirement applies to. A count above the frame, such as 4×, makes one frame apply to four identical features.
What does the standard say about a feature control frame?
The compartments, symbols and leader rules are defined in ISO 1101, datums in ISO 5459. Where the arrow ends decides what is toleranced: on the outline or on an extension line clearly separate from the dimension line, the requirement applies to the surface; in line with a dimension line, it applies to the derived feature, such as the axis or median plane. Letters in separate compartments form a datum system with precedence; A-B in one compartment is a single common datum. Two frames stacked on one feature are two requirements that both apply. In ASME Y14.5 a composite frame, one symbol spanning two rows, has its own meaning for patterns.
How does a feature control frame work in practice?
The frame sets what you have to achieve and how it is proven. The value says how tight, the datums which faces it is measured from, and so which faces are best used for locating in the final setup. A Ⓜ can add geometric tolerance as the size departs from maximum material; a second frame with a smaller value can tie features tighter to each other. On a ballooned drawing each frame usually becomes its own line in the inspection report. A requirement that only a coordinate measuring machine can prove adds inspection time, per part or per sample.
What is a feature control frame often confused with?
A feature control frame is not a basic dimension: that also sits in a box, but holds only a number, no symbol. The datum feature symbol is something else again: a letter in a square, connected to a triangle on the feature, identifies a datum; the feature control frame refers to it.
How do you see a feature control frame in Blake?
In Blake the tolerances from the drawing sit with the part as proposals. You confirm or correct them; who did so and when stays visible, with a note if you add one. More on requests.
Frequently asked questions
In what order do you read a feature control frame?
Left to right: symbol, value with any ⌀ and modifiers, then the datums. The first datum is the primary: the part is aligned on it first when measured. That is also a pointer to the locating face in the final setup.
What do two frames stacked on top of each other mean?
Two requirements that both apply, for example a looser position of a pattern relative to the datums and a tighter value for the features relative to each other. A composite frame under ASME Y14.5, one symbol spanning two rows, has a meaning of its own.
What does 4× above a feature control frame mean?
That the frame applies to four identical features, usually a hole pattern. Each feature has to meet the requirement; in the inspection report each one is usually listed separately.