12.1 All-Around, All-Over, and Limited Scope

12.1 All-Around, All-Over, and Limited Scope

Profile tolerances can apply to a single line element, an entire perimeter in a view, an entire 3-D surface, or only a portion of a surface. ASME Y14.5-2009 distinguishes these cases by the symbols placed on the leader and the auxiliary notes that bound the extent of the zone. The Senior technologist must know exactly which symbol conveys which scope because the wrong symbol expands or shrinks the tolerance zone by orders of magnitude.

All-Around Symbol

The all-around symbol is a small circle placed at the junction of the leader line and the geometry in the view where the profile is shown. It tells the inspector that the profile tolerance applies to the entire perimeter of the feature in that single view — that is, around the complete cross-sectional outline displayed, end-to-end with no interruption. The zone is still a 2-D profile zone: for profile of a line, each cross-sectional element drawn in the view must lie within two equally-disposed (or unequally disposed) boundary curves offset from the true profile. The all-around symbol does NOT make a 2-D tolerance control a 3-D volume. It simply makes the perimeter in that one view fully covered with no interruption.

For a flat part with a complex outline shown in plan view, profile of a line with all-around is a clean way to control the entire outline with one callout. For a revolved part with a profile shown in section view, all-around drives every line element at every angular position because each line element repeats the same perimeter. Be careful: if the profile feature has multiple separate views showing different elements, each view needs its own all-around symbol, or the scope covers only the view where the circle appears.

All-Over Symbol

The all-over symbol (sometimes called the extent symbol) is two concentric circles placed at the same junction. It tells the inspector that the profile tolerance applies to the entire 3-D surface — every face, every fillet, every region — of the controlled feature, not just the perimeter shown in one view. All-over is used with profile of a surface when a part's whole skin must be controlled. Because all-over sweeps the entire surface, it is the most expensive scope to verify; the inspector cannot sample only the perimeter and declare conformance.

A frequent Senior-level trap: applying the all-around symbol (single circle) to a surface that is genuinely 3-D, such as a complex casting face, when the intent was all-over (two circles). The single-circle all-around symbol only verifies the perimeter in one view; the rest of the surface is unconstrained. The reverse trap also occurs: specifying all-over when only the perimeter in one view matters adds unnecessary CMM time without design benefit.

Limited Scope: Chain Line and Between

When a profile tolerance is intended to cover only a portion of a surface, Y14.5-2009 limits the scope with a chain line (drawn as a phantom line) placed adjacent to the controlled region, plus a length dimension or reference letters. The chain line physically marks the extent on the drawing; a dimension defines its length; or the FCF carries a "BETWEEN A AND B" note that ties the extent to two designated points marked on the true profile. Outside the marked extent, the surface has no profile control from that FCF (though other controls may apply).

Between-Points Extent

The between-points extent is a specific limited-scope case. The FCF carries the note BETWEEN A AND B, and the drawing marks the two points A and B on the true profile. The profile zone applies only to the portion of the surface lying between those two points. This is useful when a surface has a critical transition region — for example, the blend between a cylinder and a cone — and the designer wants to tighten only that region.

Scope-Decision Table

Worked Scope Decision

A sheet-metal bracket has a 0.8 mm profile of a surface control on the outer flange. The drawing shows the bracket in one side view with the leader pointing at the upper flange face only. If the designer places a single circle (all-around) on that leader, the inspector verifies the upper-flange perimeter as seen in the side view only — not the underside, not the return flange. If the designer intended the entire outer skin of the bracket, the callout must use all-over (two circles) AND must clearly call out profile of a surface, not profile of a line. A field change that swaps one symbol for the other changes the verification program and the part's acceptability.

Common Traps Summary

The Senior exam frequently tests three scope mistakes. (1) Using all-around (single circle) where all-over (two circles) was intended — this leaves most of the surface unconstrained and is the most expensive misinterpretation because the part can pass while grossly out of spec on the unverified faces. (2) Reading profile of a line with all-around as if it controlled a 3-D surface — it does not; profile of a line applies line element by line element, and all-around only extends each element to the full perimeter in the view. (3) Forgetting that a limited-scope chain line or between A and B note restricts the zone; without the note the profile applies to the entire feature as drawn, and the inspector may reject good parts by measuring outside the intended extent.