KEVOS® MAKEOS · Power Transmission
Step Cone Pulley Design (Geometric Speed Steps, Step Diameters, Crossed Belt Length)
For a pair of step (cone) pulleys giving a range of output speeds, what speeds should the steps give and what diameter is each step, so one belt fits every step?
Design of matched step (cone) pulleys driven by a crossed belt: output speeds in geometric progression between the lowest and highest speed with the step ratio fitted to the number of steps (as the progression tool), the driver and driven diameter of each step with a constant diameter sum so the same crossed belt fits every step, and the belt length and wrap (as the crossed belt length tool), against the smallest pulley diameter you allow.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Driver (input) speed | rpm | Speed of the driving shaft. |
| Lowest output speed | rpm | Slowest output speed wanted. |
| Highest output speed | rpm | Fastest output speed wanted. |
| Number of steps | steps | Number of steps on each pulley. |
| Sum of driver and driven diameters | mm | Driver plus driven diameter, the same for every step with a crossed belt. |
| Centre distance | mm | Distance between the shaft centres. |
| Smallest pulley diameter allowed | mm | Smallest diameter the belt can bend round without damage. |
Method and formulas
- Step ratio r = (n_max ÷ n_min)^(1 ÷ (k − 1)); speeds n_i = n_min r^i (as the progression tool).
- Driver d₁ = S n_i ÷ (n_in + n_i); driven d₂ = S n_in ÷ (n_in + n_i), so d₁ + d₂ = S on every step.
- Crossed belt length depends only on the diameter sum, so one belt fits every step (as the crossed belt length tool).
- Example: step ratio 2; the smallest step is 80 mm and the belt 1,895.6 mm long.
Limitations
- Crossed belt for exact equal lengths; with an open belt the diameter sums differ slightly between steps.
- Belt slip of a few per cent lowers each output speed.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out step pulleys for a drill press or lathe
- Replace a worn cone pulley pair
- Choose speeds for a belt-driven machine
Who it is for
- Machine builders
- Restorers
- Design engineers
What you get
- Speed ratio and output speeds
- Diameters of each step
- Belt length and smallest pulley
Interpreting the result
- Speeds in geometric progression give the same percentage step everywhere, which suits cutting speeds on a range of diameters.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 37–39, 2473–2490. Topic reference; no source tables or recommended settings are reproduced.
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