Belt & Pulley Calculator
The Belt & Pulley Calculator computes belt length (L = 2C + Ï(Dâ+Dâ)/2 + (Dâ-Dâ)ÂČ/4C), speed ratio, belt speed, wrap angles, and tension for two-pulley drive systems. It includes an interactive SVG pulley diagram with belt path and a reference table for V-belt, timing belt, and flat belt types â free, no signup required.
Pulley System Parameters
Belt Type Reference
| Belt Type | Max Speed (ft/min) | Efficiency | Application |
|---|---|---|---|
| V-Belt (A) | 6,500 | 95% | Light duty, HVAC, small machines |
| V-Belt (B) | 6,500 | 95% | Medium duty, industrial fans, pumps |
| V-Belt (C) | 6,500 | 95% | Heavy duty, compressors, large pumps |
| V-Belt (D) | 6,500 | 94% | Extra heavy duty, crushers, mills |
| Flat Belt | 10,000 | 98% | High speed, precision machinery |
| Timing Belt (HTD) | 16,000 | 98% | Synchronous, no slip, CNC, 3D printers |
| Ribbed (Poly-V) | 10,000 | 97% | Automotive, compact drives |
| Round Belt | 5,000 | 90% | Light conveyors, sewing machines |
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What is a Belt & Pulley System?
A belt and pulley system transmits rotational power between two shafts using a flexible belt wrapped around pulleys. The belt length for a two-pulley system is L = 2C + Ï(Dâ+Dâ)/2 + (DââDâ)ÂČ/(4C), where C is the center distance and Dâ, Dâ are pulley diameters. The speed ratio equals the diameter ratio: RPMâ/RPMâ = Dâ/Dâ. V-belts are the most common type, suitable for speeds up to 6,500 ft/min. Wrap angle (the arc of contact) should be at least 120° on the smaller pulley to prevent slippage.
How to Use This Calculator
- Enter the driver (motor) pulley diameter and the driven (load) pulley diameter in mm
- Enter the center-to-center distance between the two pulley shafts
- Enter the driver RPM (motor speed) and transmitted power in kW
- Click Calculate to see belt length, speed ratio, driven RPM, belt speed, and wrap angles
- Review the SVG pulley diagram for a visual representation of the system geometry
Frequently Asked Questions
How do I calculate belt length for a two-pulley system?
Use the formula L = 2C + Ï(Dâ+Dâ)/2 + (DââDâ)ÂČ/(4C), where C is the center distance and Dâ, Dâ are the pulley diameters. This gives the pitch length of the belt. For standard V-belts, select the nearest available belt number (e.g., A68, B75) from the manufacturer's catalog.
What is the minimum wrap angle for a pulley?
The minimum recommended wrap angle is 120° (2.09 radians) on the smaller pulley. Below this, the belt may slip under load even with proper tension. If the diameter difference between pulleys is very large, increase the center distance or use an idler pulley to increase the wrap angle.
V-belt vs timing belt â which should I use?
V-belts are simpler, cheaper, and absorb shock and vibration â ideal for general industrial drives and HVAC systems. Timing belts (synchronous belts) provide positive engagement with no slippage, making them necessary for applications requiring exact speed synchronization like CNC machines, 3D printers, and engine camshaft drives.
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