Regardless Of Feature Size
Is RFS a special modifier that must be added to the drawing?
No. RFS is the default implied condition when no MMC or LMC modifier is specified on a geometric tolerance for a feature of size.
Does RFS create bonus tolerance?
No. Bonus tolerance is associated with MMC or LMC relationships, not RFS.
Why does RFS matter in CNC machining?
It determines whether geometry is fixed or size-dependent during inspection, which directly affects process capability, tooling strategy, and acceptance criteria on production parts.
Regardless of Feature Size (RFS) is the default GD&T condition where a geometric tolerance applies independently of the actual size of the feature. No bonus tolerance is gained as the feature moves toward MMC or LMC. If no material modifier is shown in the feature control frame, RFS is assumed. This means the part must meet both size and geometric tolerances simultaneously with no extra allowance.
In a CNC machining environment, RFS forces the programmer and machinist to control geometry across the full size range of a feature. For example, a hole with a position tolerance under RFS must remain within the specified position zone whether the hole is near its low or high size limit. This often leads to parts that pass size checks with calipers but fail CMM inspection due to excessive position error. RFS is commonly used when consistent geometry is critical, such as in locating hole patterns. Because no bonus tolerance is available, tool wear, fixture drift, thermal growth, and spindle runout must be controlled aggressively. Any setup error directly consumes the full geometric tolerance budget under RFS, making workholding precision paramount. This impacts process planning and inspection strategies, requiring tighter tolerances on setups and machining parameters.
Mistaking size tolerance for positional tolerance: A machinist may hit diameter or width but miss position because RFS does not add bonus tolerance; the result is a dimensionally acceptable feature that still fails function or CMM inspection.
Assuming MMC behavior when none is specified: Shops sometimes inspect as if extra tolerance is available near MMC, but under RFS that assumption is wrong, which can lead to false accepts in first-article or in-process inspection.
Overlooking datum transfer and setup error: Under RFS, any fixture or workholding error directly consumes the full geometric tolerance budget because no material-condition relief exists, so a small clamping shift or probe setup error can scrap parts even when the toolpath is nominal.