BIZOMAT MAKEOS · Gears
Involute Spline Basic Dimensions (ANSI B92.1)
What are the basic diameters and space width of this involute spline?
Pitch, base, major, minor and form diameters, circular pitch and minimum effective space width of 30° and 37.5° involute splines by the ANSI B92.1 basic formulas, for side-fit and major-diameter-fit variants.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Diametral pitch P (e.g. 16 for 16/32) | 1/in | Diametral pitch (the first number of the pitch fraction). |
| Number of teeth | teeth | Number of teeth. |
| Spline type | choice | Pressure angle, root form and fit. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Diametral pitch P (e.g. 16 for 16/32)
- What it is
- The diametral pitch of the spline, the first number of its pitch fraction (16 in 16/32): teeth per inch of pitch diameter.
- Units and format
- Enter a number in 1/in: threads per inch. The form accepts 0.000001 1/in to 128 1/in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 16 1/in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All diameters are inversely proportional to the diametral pitch.
- Get it right
- Enter only the first number of the fraction; the second number (stub pitch) is always twice it.
What this means: Number of teeth
- What it is
- The number of teeth on the spline, equal for the shaft (external) and hub (internal) parts.
- Units and format
- Enter a number in teeth: a whole number of teeth. The form accepts 6 teeth to 100 teeth. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 teeth as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pitch diameter is directly proportional to the number of teeth.
- Get it right
- Count the teeth around the full circumference, not the spaces on one side.
What this means: Spline type
- What it is
- The pressure angle, root form and fit of the spline: 30° with flat or fillet root, side fit or major diameter fit, or 37.5° fillet root side fit.
- Units and format
- Choose one of 4 options from the list: 30° flat root, side fit; 30° flat root, major diameter fit; 30° fillet root, side fit; 37.5° fillet root, side fit.
- Example
- The form opens with “30° flat root, side fit” selected as a worked example. Choose the option that matches your case.
- Get it right
- Take it from the spline designation on the drawing; the root and fit change the major and minor diameters.
Method and formulas
- D = N/P; D_b = D cos φ; circular pitch = π/P; minimum effective space width = π/2P (30°) or (0.5π + 0.1)/P (37.5°).
- Major and minor diameters by fit type, e.g. 30° flat root side fit: D_ri = (N + 1.35)/P, D_o = (N + 1)/P, D_i = (N − 1)/P, D_re = (N − 1.35)/P.
- Form clearance c_F = 0.001D (0.002–0.010 in); form diameters D_Fi = (N + 1)/P + 2c_F, D_Fe = (N − 1)/P − 2c_F (major-fit and 37.5° variants differ).
- Example: 20 teeth at 16/32 pitch have D = 1.25 in and an external major diameter of 1.3125 in.
Limitations
- Basic dimensions only; tolerances, effective and actual space widths for each fit class come from the full standard.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out a spline shaft and hub
- Check spline blanks before cutting
- Find form diameters for tool design
Who it is for
- Gear designers
- Machinists
- Maintenance engineers
What you get
- Pitch and base diameters
- Internal and external major and minor diameters
- Form diameters and form clearance
- Circular pitch and minimum effective space width
Interpreting the result
- Use the minimum effective space width with the standard’s tolerances to set gauge sizes.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2255–2282. Topic reference; no source tables or recommended settings are reproduced.
- ANSI B92.1 Involute Splines and Inspection
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