Machinery's Handbook, 31st Edition
Involute Splines 2341 tooth thickness, which exceeds the actual tooth thickness by the amount of the effective variation. The effective space width of the internal spline minus the effective tooth thickness of the external spline is the effective clearance and defines the fit of the mating parts. (This state ment is strictly true only if high points of mating parts come into contact.) Positive effec tive clearance represents looseness or backlash. Negative effective clearance represents tightness or interference. Space Width and Tooth Thickness Limits.— The variation of actual space width and actual tooth thickness within the machining tolerance causes corresponding variations of effec- tive dimensions, so that there are four limit dimensions for each component part. These variations are shown diagrammatically in Table 5. Table 5. Specification Guide for Space Width and Tooth Thickness ANSI B92.1-1996 Dimensions of Variations, Clearances, and Tolerances on Part Dimensioning Method
Alternatives
Standard
Dimension
Effective
Actual
A Required
B Ref.
Max
Required
Space Width of Internal Spine
m
c v Max
λ
Ref. Ref.
Ref.
Ref.
Min
Max
Required
Required
λ
m m
Min Max
2 P π
(Basic)
Required
Required
Required
λ
Tooth Thickness of External Spine
Min
Ref. Ref.
Required
Required
Max
Ref.
Ref. Ref.
λ m
c v Min = 0
Required
Required
Min
The minimum effective space width is always basic. The maximum effective tooth thickness is the same as the minimum effective space width except for the major diameter fit. The major diameter fit maximum effective tooth thickness is less than the minimum effective space width by an amount that allows for eccentricity between the effective spline and the major diameter. The permissible variation of the effective clearance is divided between the internal and external splines to arrive at the maximum effective space width and the minimum effective tooth thickness. Limits for the actual space width and actual tooth thickness are constructed from suitable variation allowances. Use of Effective and Actual Dimensions.— Each of the four dimensions for space width and tooth thickness shown in Table 5 has a definite function. Minimum Effective Space Width and Maximum Effective Tooth Thickness: These dimensions control the minimum effective clearance, and must always be specified. Minimum Actual Space Width and Maximum Actual Tooth Thickness: These dimensions cannot be used for acceptance or rejection of parts. If the actual space width is less than the minimum without causing the effective space width to be undersized, or if the actual tooth thickness is more than the maximum without causing the effective tooth thickness to be oversized, the effective variation is less than anticipated; such parts are desirable and not defective. The specification of these dimensions as processing reference dimensions is optional. They are also used to analyze undersize effective space width or oversize effective tooth thickness conditions to determine whether or not these conditions are caused by excessive effective variation. Maximum Actual Space Width and Minimum Actual Tooth Thickness: These dimensions control machining tolerance and limit the effective variation. The spread between these
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