KEVOS® MAKEOS · Power Transmission
Sprocket Bore and Key Plan (Sprocket Diameters, Shaft Keyseat Readings, Wall Under the Teeth)
For a roller chain sprocket bored and keyed to a shaft, what are its diameters and keyseat readings, and is there enough metal left between the keyway and the tooth roots?
Plan of a roller chain sprocket blank and its shaft key: the pitch, bottom, caliper and outside diameters of the sprocket (as the sprocket diameters tool), the chordal height, keyseat measurement S and measurement over the key T for the shaft (as the keyseat depth tool), and the wall left between the top of the key (where the hub keyway reaches) and the bottom diameter of the teeth, against the least wall you will accept.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Chain pitch | mm | Pitch of the roller chain. |
| Number of teeth | teeth | Number of teeth on the sprocket. |
| Roller diameter | mm | Roller diameter of the chain. |
| Shaft and key | ||
| Shaft (bore) diameter | mm | Shaft diameter, equal to the sprocket bore. |
| Key width | mm | Width of the key. |
| Shaft keyseat depth at the side | mm | Depth of the shaft keyseat measured at its side. |
| Key height | mm | Height of the key. |
| Least wall under the teeth | mm | Smallest radial wall you will accept between the hub keyway and the tooth bottoms. |
Method and formulas
- Pitch diameter = p ÷ sin (180° ÷ N); bottom = PD − D_r; caliper = PD cos (90° ÷ N) − D_r for odd teeth; outside = p (0.6 + cot (180° ÷ N)) (as the sprocket diameters tool).
- Chordal height Y = (D − √(D² − w²)) ÷ 2; S = D − Y − t; T = S + h (as the keyseat depth tool).
- Top of the key from the bore centre = T − D ÷ 2; wall = bottom diameter ÷ 2 − (T − D ÷ 2).
- Example: bottom diameter 76.235 mm; keyseat reading S 25.457 mm; 20.661 mm of wall under the teeth.
Limitations
- Plain hub without a raised boss; a hub boss adds metal beside the teeth but not under them.
- Hub keyway depth taken to the top of the key; add the keyway clearance from your key standard.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the largest bore for a small sprocket
- Set the keyseat readings for a sprocket shaft
- Rebore a stock sprocket for a bigger shaft
Who it is for
- Machinists
- Maintenance fitters
- Design engineers
What you get
- Sprocket diameters
- Shaft keyseat readings
- Wall under the teeth
Interpreting the result
- A thin wall under a keyway is where small sprockets crack; go up a tooth or two or use a smaller key with a set screw.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2537–2550, 2460–2486. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
