Ⓡ Regardless of feature boundary (RFB)
Regardless of feature boundary (RFB) · Modificadores de zona · ASME Y14.5
Example in plan
How to interpret it
On the drawing, “⌓ 0.3 with regardless of feature boundary modifier in ASME note” states a regardless of feature boundary (rfb) requirement.
What controls
An ASME concept that applies to irregular features of size, those closed contours that act as an internal or external feature but are not a cylinder or a pair of parallel faces (a shaped pocket, a profiled boss, a cam). When a profile controls one of those features, regardless of feature boundary means the tolerance zone applies as-is, with no allowance gained from how the actual size of the contour turned out: there is no bonus. It is the default condition, just as regardless of feature size is for a regular feature of size; it only changes if the feature control frame carries a material modifier, in which case the boundary can grow or shrink. What it does NOT mean is that the size of the contour stops mattering: it is still governed by its own profile or by whatever dimensions it has; what does not happen is the trade-off between size and geometry.
How to verify
It is measured like a normal profile, but in the software you must make sure the evaluation is done without a material modifier: if the program applies bonus based on the size of the contour, it is accepting parts that do not conform. Scanning or dense probing of the contour, alignment to the drawing's datum reference frame and comparison against the theoretical profile. A fixed-contour functional gauge is not the right verification, because that type of gauge embodies precisely a maximum material boundary, which is the opposite of what is being asked for.
Common mistakes when interpreting it
- Expecting bonus from the size of the contour: without a material modifier there is none; the zone is what the feature control frame states.
- Reading the Ⓡ glyph on an ISO drawing as regardless of feature boundary: there it stands for reciprocity, which is a different concept.
- Verifying with a fixed-contour gauge, which imposes a maximum material boundary that this criterion does not contemplate.
How to get it in the workshop / if it comes out of tolerance
Advanced ASME. If it appears on a profile of a surface, do not assume coupling with the ± size dimension. Watch out: the same Ⓡ glyph on an ISO drawing is not RFB — it is the “reciprocity requirement” (ISO 1101), a different concept. Check whether the drawing cites ISO or ASME before interpreting it. On the shop floor the reading is simple and strict: there is no extra allowance to recover here, so the profile must be achieved exactly as written and it pays to program aiming at the center of the zone.
Since there is no size-based allowance, all the effort goes into the process: cutter radius compensation, tool wear, deflection on thin walls and finishing strategy in the corners, which is where the deviation concentrates. Center the result in the zone instead of pushing it to one side, because there is no cushion here. If the contour fails uniformly, correct the offset; if it fails in certain areas, look at the tool and workholding rigidity in that part of the workpiece.
Alternative symbol:RFB
Related symbols
Other symbols in Zone modifiers
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