KEVOS® MAKEOS · Power Transmission
Silent Chain Sprocket Inspection (Over-Pin Diameter, Eccentricity and Guide Groove Tolerances)
Does a cut silent (inverted-tooth) chain sprocket of 3/8 in pitch or larger pass inspection: is the measured over-pin diameter within its tolerance, the run-out of the pitch diameter to the bore within its limit, and the guide groove within its size?
Inspection of silent chain sprockets for 3/8 in and larger pitch by the ANSI B29.2M rules in the handbook: the nominal pitch diameter P ÷ sin(180°/N), outside diameter for rounded teeth P(cot 180°/N + 0.08), blank diameter, over-pin diameter over 0.625P gauge pins (even and odd numbers of teeth), the over-pin tolerance (0.004 + 0.001 P √N) in, all negative, the eccentricity of the pitch diameter to the bore 0.001 × PD but not less than 0.006 nor more than 0.032 in total indicator reading, and the maximum guide groove diameter P(cot 180°/N − 1.16) with its +0, −0.030 in tolerance, against your measurements.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Chain pitch | mm | Pitch of the silent chain the sprocket is cut for, 3/8 in (9.525 mm) or larger; 1 in is 25.4 mm. |
| Number of teeth | teeth | Number of teeth on the sprocket. |
| Measured | ||
| Measured over-pin diameter (over 0.625P pins) | mm | Diameter measured over two gauge pins of diameter 0.625 × pitch placed in opposite tooth spaces (or the nearest spaces for an odd number of teeth). |
| Measured run-out of the pitch diameter to the bore (TIR) | mm | Total indicator reading of the pitch diameter (over pins or teeth) with the sprocket turned on its bore. |
| Measured guide groove diameter | mm | Diameter measured at the bottom of the guide groove. |
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: Chain pitch
- What it is
- Pitch of the silent chain the sprocket is cut for, 3/8 in (9.525 mm) or larger.
- Units and format
- Enter a number in mm: millimetres. The form accepts 9.5 mm to 51 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All diameters and the tolerance grow with the pitch.
- Get it right
- Read it from the chain number: SC8 is 1 in pitch, SC4 is 1/2 in.
What this means: Number of teeth
- What it is
- Number of teeth on the sprocket being inspected.
- Units and format
- Enter a number in teeth: a whole number of teeth. The form accepts 17 teeth to 400 teeth. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 teeth as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets every diameter and widens the over-pin tolerance with √N.
- Get it right
- Count them; odd numbers of teeth use the odd-tooth over-pin formula.
Measured
What this means: Measured over-pin diameter (over 0.625P pins)
- What it is
- Diameter measured over two gauge pins of 0.625 × pitch placed in opposite tooth spaces.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 209.85 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the sprocket above nominal or below the lower limit.
- Get it right
- For an odd number of teeth use the spaces nearest to opposite; take the largest reading.
What this means: Measured run-out of the pitch diameter to the b…
- What it is
- Total indicator reading of the pitch diameter with the sprocket turned on its bore.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the sprocket when it exceeds the eccentricity limit.
- Get it right
- Mount the sprocket on an arbor in its bore and indicate over pins or the teeth.
What this means: Measured guide groove diameter
- What it is
- Diameter measured at the bottom of the guide groove for the chain guide links.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 171.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the sprocket outside +0, −0.030 in of the maximum groove diameter.
- Get it right
- Measure across the groove bottom with a groove micrometer or calipers.
Method and formulas
- PD = P ÷ sin(180°/N); outside diameter (rounded teeth) = P(cot 180°/N + 0.08); blank diameter 0.020 in larger.
- Gauge pin Dp = 0.625P; over-pin diameter, even N: PD − 0.125P csc(30° − 180°/N) + 0.625P; odd N: cos(90°/N)(PD − 0.125P csc(30° − 180°/N)) + 0.625P.
- Over-pin tolerance (all negative) = (0.004 + 0.001 P √N) in, P in inches; the handbook Table 4a lists it by bands of tooth numbers.
- Eccentricity of the pitch diameter to the bore: 0.001 × PD, not less than 0.006 in nor more than 0.032 in TIR.
- Maximum guide groove diameter G = P(cot 180°/N − 1.16), tolerance +0, −0.030 in.
- Example: a 25-tooth sprocket for 25.4 mm pitch has a nominal over-pin diameter of 209.96 mm, accepted down to 209.73 mm.
Limitations
- For 3/8 in and larger pitch; 3/16 in pitch chain uses 0.667P pins, other constants and its own Table 4b.
- Tooth form, face width and the tooth profile are checked against the tooth form drawing (silent-chain-sprocket-tooth-form).
- The tolerance by the formula at the actual number of teeth can differ from the table band value by up to 0.001 in.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Accept or reject cut silent chain sprockets
- Set the limits for an inspection sheet
- Check a worn or reworked sprocket
Who it is for
- Quality inspectors
- Gear and sprocket cutters
- Maintenance fitters
What you get
- Nominal pitch, outside, blank and over-pin diameters
- Over-pin tolerance and limits
- Eccentricity limit
- Guide groove limits
- Accept or reject
Interpreting the result
- An over-pin diameter above nominal means the teeth are thick and the chain will ride high; below the limit, the chain sits too deep and the pitch line moves.
- Run-out shows as a once-per-revolution tension and speed pulse in the chain.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3458–3464. Topic reference; no source tables or recommended settings are reproduced.
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