ANSI B This circle along with the tooth tip circle or start of chamfer circle determines the limits of tooth profile requiring control. It is located near the major circle on the internal spline and near the minor circle on the external spline. Form Clearance cF is the radial depth of involute profile beyond the depth of engagement with the mating part. It allows for looseness between mating splines and for eccentricities between the minor circle internal , the major circle external , and their respective pitch circles.

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ANSI B This circle along with the tooth tip circle or start of chamfer circle determines the limits of tooth profile requiring control. It is located near the major circle on the internal spline and near the minor circle on the external spline. Form Clearance cF is the radial depth of involute profile beyond the depth of engagement with the mating part. It allows for looseness between mating splines and for eccentricities between the minor circle internal , the major circle external , and their respective pitch circles.

Internal Spline is a spline formed on the inner surface of a cylinder. Involute Spline is one having teeth with involute profiles. Lead Variation is the variation of the direction of the spline tooth from its intended direction parallel to the reference axis, also including parallelism and alignment variations see Fig. Note: Straight nonhelical splines have an infinite lead. Length of Engagement Lq is the axial length of contact between mating splines. Machining Tolerance m is the permissible variation in actual space width or actual tooth thickness.

Major Circle is the circle formed by the outermost surface of the spline. It is the outside circle tooth tip circle of the external spline or the root circle of the internal spline. Major Diameter Do, Dri is the diameter of the major circle. Minor Circle is the circle formed by the innermost surface of the spline. It is the root circle of the external spline or the inside circle tooth tip circle of the internal spline.

Minor Diameter Dre, Di is the diameter of the minor circle. Nominal Clearance is the actual space width of an internal spline minus the actual tooth thickness of the mating external spline. It does not define the fit between mating members, because of the effect of variations.

Out of Roundness is the variation of the spline from a true circular configuration. Parallelism Variation is the variation of parallelism of a single spline tooth with respect to any other single spline tooth see Fig. Pitch Circle is the reference circle from which all transverse spline tooth dimensions are constructed. Pitch Diameter D is the diameter of the pitch circle. Pitch Point is the intersection of the spline tooth profile with the pitch circle.

Unless otherwise specified, it is the standard pressure angle. Profile Variation is any variation from the specified tooth profile normal to the flank. Spline is a machine element consisting of integral keys spline teeth or keyways spaces equally spaced around a circle or portion thereof.

Stub Pitch Ps is a number used to denote the radial distance from the pitch circle to the major circle of the external spline and from the pitch circle to the minor circleof the internal spline. The stub pitch for splines in this standard is twice the diametral pitch. Total Index Variation is the greatest difference in any two teeth adjacent or otherwise between the actual and the perfect spacing of the tooth profiles. The numerator in this fractional designation is known as the diametral pitch and controls the pitch diameter; the denominator, which is always double the numerator, is known as the stub pitch and controls the tooth depth.

For convenience in calculation, only the numerator is used in the formulas given and is designated as P. Diametral pitch, as in gears, means the number of teeth per inch of pitch diameter. Table 1 shows the symbols and Table 2 the formulas for basic tooth dimensions of involute spline teeth of various pitches. Basic dimensions are given in Table 3. Table 1. In selecting the number of teeth for a given spline application, it is well to keep in mind that there are no advantages to be gained by using odd numbers of teeth and that the diameters of splines with odd tooth numbers, particularly internal splines, are troublesome to measure with pins since no two tooth spaces are diametrically opposite each other.

Types and Classes of Involute Spline Fits. Dimensional data for flat root side fit, flat root major diameter fit, and fillet root side fit splines are tabulated in this standard for degree pressure angle splines; but for only the fillet root side fit for Side Fit: In the side fit, the mating members contact only on the sides of the teeth; major and minor diameters are clearance dimensions. The tooth sides act as drivers and centralize the mating splines.

Major Diameter Fit: Mating parts for this fit contact at the major diameter for centralizing. The sides of the teeth act as drivers. The minor diameters are clearance dimensions. The major diameter fit provides a minimum effective clearance that will allow for contact and location at the major diameter with a minimum amount of location or centralizing effect by the sides of the teeth.

The major diameter fit has only one space width and tooth thickness tolerance which is the same as side fit Class 5. A fillet root may be specified for an external spline, even though it is otherwise designed to the flat root side fit or major diameter fit standard. An internal spline with a fillet root can be used only for the side fit.

Classes of Tolerances. This has been done to provide a range of tolerances for selection to suit a design need. The classes are variations of the former single tolerance which is now Class 5 and are based on the formulas shown in the footnote of Table 4. All tolerance classes have the same minimum effective space width and maximum effective tooth thickness limits so that a mix of classes between mating parts is possible.

Variation 0. Flat Root Splines: are suitable for most applications. The fillet that joins the sides to the bottom of the tooth space, if generated, has a varying radius of curvature.

Specification of this fillet is usually not required. It is controlled by the form diameter, which is the diameter at the deepest point of the desired true involute form sometimes designated as TIF. When flat root splines are used for heavily loaded couplings that are not suitable for fillet root spline application, it may be desirable to minimize the stress concentration in the flat root type by specifying an approximate radius for the fillet.

Because internal splines are stronger than external splines due to their broad bases and high pressure angles at the major diameter, broaches for flat root internal splines are normally made with the involute profile extending to the major diameter.

Fillet Root Splines: are recommended for heavy loads because the larger fillets provided reduce the stress concentrations. The curvature along any generated fillet varies and cannot be specified by a radius of any given value.

External splines may be produced by generating with a pinion-type shaper cutter or with a hob, or by cutting with no generating motion using a tool formed to the contour of a tooth space. External splines are also made by cold forming and are usually of the fillet root design. Internal splines are usually produced by broaching, by form cutting, or by generating with a shaper cutter. Even when full-tip radius tools are used, each of these cutting methods produces a fillet contour with individual characteristics.

Generated spline fillets are curves related to the prolate epicycloid for external splines and the prolate hypocycloid for internal splines.

These fillets have a minimum radius of curvature at the point where the fillet is tangent to the external spline minor diameter circle or the internal spline major diameter circle and a rapidly increasing radius of curvature up to the point where the fillet comes tangent to the involute profile.

Chamfers and Corner Clearance: In major diameter fits, it is always necessary to provide corner clearance at the major diameter of the spline coupling.

This clearance is usually effected by providing a chamfer on the top corners of the external member. This method may not be possible or feasible because of the following: A If the external member is roll formed by plastic deformation, a chamfer cannot be provided by the process. B A semitopping cutter may not be available. C When cutting external splines with small numbers of teeth, a semitopping cutter may reduce the width of the top land to a prohibitive point.

In such conditions, the corner clearance can be provided on the internal spline, as shown in Fig. When this option is used, the form diameter may fall in the protuberance area.

Internal corner clearance. Spline Variations. This is either the pitch point or the contact point of the standard measuring pins. Profile variation is positive in the direction of the space and negative in the direction of the tooth. Profile variations may occur at any point on the profile for establishing effective fits and are shown in Table 4.

Lead Variations: The lead tolerance for the total spline length applies also to any portion thereof unless otherwise specified. Out of Roundness: This condition may appear merely as a result of index and profile variations given in Table 4 and requires no further allowance. However, heat treatment and deflection of thin sections may cause out of roundness, which increases index and profile variations.

Tolerances for such conditions depend on many variables and are therefore not tabulated. Eccentricity: Eccentricity of major and minor diameters in relation to the effective diameter of side fit splines should not cause contact beyond the form diameters of the mating splines, even under conditions of maximum effective clearance.

This standard does not establish specific tolerances. Eccentricity of major diameters in relation to the effective diameters of major diameter fit splines should be absorbed within the maximum material limits established by the tolerances on major diameter and effective space width or effective tooth thickness. This standard does not include allowances for eccentric location.

Effect of Spline Variations. Index Variations: These variations cause the clearance to vary from one set of mating tooth sides to another. Because the fit depends on the areas with minimum clearance, index variations reduce the effective clearance. Profile Variations: Positive profile variations affect the fit by reducing effective clearance. Negative profile variations do not affect the fit but reduce the contact area. Lead Variations: These variations will cause clearance variations and therefore reduce the effective clearance.

Variation Allowance: The effect of individual spline variations on the fit effective variation is less than their total, because areas of more than minimum clearance can be altered without changing the fit. The variation allowance is 60 percent of the sum of twice the positive profile variation, the total index variation and the lead variation for the length of engagement. The variation allowances in Table 4 are based on a lead variation for an assumed length of engagement equal to one-half the pitch diameter.

Adjustment may be required for a greater length of engagement. Effective and Actual Dimensions. To allow the perfect external spline to fit in any position, all spaces of the internal spline must then be widened by the amount of interference.


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Related Resources: gears. Gear Design and Engineering. American National Standard Involute Splines - These splines or multiple keys are similar in form to internal and external involute gears. In general manufacturing external splines is facilitated either by hobbing, rolling, or on a gear shaper, and internal splines either by broaching or on a gear shaper. The internal spline is held to basic dimensions and the external spline is varied to control the fit. Involute splines have maximum strength at the base, can be accurately spaced and are self-centering, thus equalizing the bearing and stresses, and they can be measured and fitted accurately. Note: All spline specification table dimensions in the standard are derived from these basic formulas by application of tolerances.


ANSI B92.1



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