Guide pulleys redirect the two leaves of a flat belt between perpendicular shafts. This animation shows a continuous four-pulley route, with each guide oriented to the belt span it redirects. The calculator determines belt surface speed from drive diameter and shaft speed.
Belt at Right Angles via Guide Pulleys Interactive Calculator
Adjust drive diameter and speed. Follow the belt around both guide pulleys and compare its surface speed with a stated reference value.
Equation Used
- No slip between drive pulley and belt.
- Diameter is the effective contact diameter in millimetres.
- The illustrated guide and driven pulley dimensions are fixed examples.
- No prediction of belt tension, fatigue, tracking or permissible power.
Brown movement 3 provides the two-guide routing principle. This illustration uses a spatial route with a separate guide for each leaf. The 30 m/s comparison is not a manufacturer rating.
How the two guides redirect the belt
The belt leaves the driver, turns around a guide, passes around the driven pulley, then returns through the second guide. Each guide redirects one leaf of the same continuous belt. The main shafts are perpendicular; the guide shafts follow their local belt planes.
The animation joins circular pulley wraps with tangent straight spans. The ribbon twists where the pulley planes differ, and its moving marks circulate at one consistent speed. Each pulley rotates in proportion to belt travel divided by its radius.
Where guide pulleys help
Guides allow power to pass between shafts where a direct belt route is inconvenient. They also add bearings and belt bending, so their size and position must suit the belt construction. Historical line-shaft layouts illustrate the principle; this diagram is not a specified modern drive assembly.
Belt surface speed
v = π D N / 60000, where D is drive diameter in mm and N is shaft speed in rpm. The result is metres per second. This follows directly from pulley circumference multiplied by revolutions per second.
The additional tiles compare v with 30 m/s. They do not establish a permissible operating speed. Use the belt and pulley manufacturer’s applicable limits for an actual design.
Worked example
For D = 200 mm and N = 1450 rpm, v = π × 200 × 1450 / 60000 = 15.18 m/s. That is 50.6% of the displayed 30 m/s reference. It is 14.82 m/s below that reference, without implying a rated safety margin.
What the guides change
The guides permit a different route and add wrap or change a span direction. They do not change the ideal surface speed imposed by the driver. Added bearings, belt bending and three-dimensional alignment remain design considerations. A geared right-angle drive is an alternative where a belt route is unsuitable.
Questions about the model
Why are there two guide pulleys?
Each redirects a separate leaf of the continuous belt, following the principle in Brown movement 3.
Does a result below 30 m/s mean the belt is suitable?
No. That number is a reference comparison. Belt construction, joint, pulley diameters, load and duty determine suitability.
Does guide size alter the ideal belt speed?
No. It changes guide rotational speed and bending conditions. Belt surface speed is set by the drive pulley when slip is neglected.
Construction reference
Henry T. Brown, 507 Mechanical Movements, movement 3: one guide pulley for each leaf of the belt between right-angle shafts.
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