Gears And Splines

Each tolerance of orientation or position and datum reference specified for features other than screw threads, such as gears and splines, must designate the specific feature of the gear or spline to which each applies (such as MAJOR DIA, PITCH DIA, or MINOR DIA). This information is stated beneath the feature control frame or beneath the datum feature symbol, as applicable.


Depending upon its function, a feature is controlled by size and applicable geometric controls. Material condition (MMC or LMC) may also be applicable. Consideration must be given to the collective effects of MMC and applicable tolerances in determining the clearance between parts (fixed or floating fastener formula) and in establishing gage feature sizes. Consideration must be given to the collective effects of LMC and applicable tolerances in determining guaranteed area of contact, thin wall conservation, and alignment hole location in establishing gage feature sizes.

2.11.1 Virtual Condition. From para. 2.11 considerations, constant value outer locus and constant value inner locus values are derived and termed virtual condition. See Figs. 2-7 through 2-12.

2.11.2 Resultant Condition. From para. 2.11 considerations, the worst case inner locus and worst case outer locus values are derived and termed resultant condition. See Figs. 2-7 through 2-12.

2.11.3 Datum Features at Virtual Condition.

A virtual condition exists for a datum feature of size where its axis or center plane is controlled by a geometric tolerance. In such cases, the datum feature applies at its virtual condition even though it is referenced in a feature control frame at MMC or LMC. Where a virtual condition equal to the maximum material condition or the least material condition is the design requirement, a zero tolerance at MMC or LMC is specified. See Sections 4, 5, and 6.


Where an angular surface is defined by a combination of a linear dimension and an angle, the surface must lie within a tolerance zone represented b> two nonparallel planes. Sec Fig. 2-13. The tolerance zone will widen as the distance from the apex of the angle increases. Where a tolerance zone with parallel boundaries is desired, a basic angle may be specified as in Fig. 2-14. The dimensions related to the origin arc then used in the same manner described in para. 2.6.1. Additionally, an angularity tolerance may be specified within these boundaries. See Fig. 6-27.


Conical tapers include the category of standard machine tapers used throughout the tooling industry, classified as American Standard Self-Holding and Steep Taper series. See ANSI B5.10. American Standard machine tapers are usually dimensioned by specifying the taper name and number. See Fig. 2-16(b). The diameter at the gage line and the length may also be specified. The taper in inches per foot and the diameter of the small end may be shown as reference. A conical taper may also be specified by one of the following methods:

(a) a basic taper and a basic diameter (see Fig. 2-15);

(b) a size tolerance combined with a profile of a surface tolerance applied to the taper (see para. 6.5.8);

(c) a toleranced diameter at both ends of a taper and a toleranced length. See Fig. 2-16(a).

NOTE: The method described in (c) above is applicable for non-critical tapers, such as the transition between diameter┬╗ of a shaft.

(d) a composite profile tolerance.

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