Machinery's Handbook, 31st Edition
2344
Involute Splines
Exceptions: a) The external major diameter, unless chamfered or reduced, may interfere with the internal form diameter on flat root side fit splines. Internal splines made to the 1957 and 1960 standards had the same dimensions as shown for the major diameter fit splines in this standard. b) For 15 teeth or less, the minor diameter of the internal spline, unless chamfered, will interfere with the form diameter of the external spline. c) For 9 teeth or less, the minor diameter of the internal spline, unless chamfered, will interfere with form diameter of the external spline. d) The internal minor diameter, unless chamfered, will interfere with the external form diameter. e) The internal minor diameter, unless chamfered, will interfere with the external form diameter. f) For 10 teeth or less, the minimum chamfer on the major diameter of the external spline may not clear the internal form diameter. g) Depending upon the pitch of the spline, the minimum chamfer on the major diameter may not clear the internal form diameter. Drawing Data.— It is important that uniform specifications be used to show complete information on detail drawings of splines. Much misunderstanding will be avoided by following the suggested arrangement of dimensions and data as given in Table 6. The number of x’s indicates the number of decimal places normally used. With this tabulated type of spline specifications, it is usually not necessary to show a graphic illustration of the spline teeth. Spline Data and Reference Dimensions.— Spline data are used for engineering and manu- facturing purposes. Pitch and pressure angle are not subject to individual inspection. As used in this standard, reference is an added notation or modifier to a dimension, spec ification, or note when that dimension, specification, or note is: 1) Repeated for drawing clarification. 2) Needed to define a nonfeature datum or basis from which a form or feature is generated. 3) Needed to define a nonfeature dimension from which other specifications or dimen sions are developed. 4) Needed to define a nonfeature dimension at which toleranced sizes of a feature are specified. 5) Needed to define a nonfeature dimension from which control tolerances or sizes are developed or added as useful information. Any dimension, specification, or note that is noted “REF” should not be used as a crite rion for part acceptance or rejection. Estimating Key and Spline Sizes and Lengths.— Fig. 3 may be used to estimate the size of American Standard involute splines required to transmit a given torque. It also may be used to find the outside diameter of shafts used with single keys. After the size of the shaft is found, the proportions of the key can be determined from Table 1 on page 2551 . Curve A is for flexible splines with teeth hardened to 55 to 65 RC (Rockwell C scale). For these splines, lengths are generally made equal to or somewhat greater than the pitch diameter for diameters below 1 1 ∕ 4 inches; on larger diameters, the length is generally one- third to two-thirds the pitch diameter. Curve A also applies for a single key used as a fixed coupling, the length of the key being one to one and one-quarter times the shaft diameter. The stress in the shaft, neglecting stress concentration at the keyway, is about 7500 pounds per square inch. See also Effect of Keyways on Shaft Strength starting on page 301 .
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