Mechanical Design Handbook

Key Geometric Calculations In Part 2 , we analyzed the loads. Now, we must size the geometry. Designing a chain drive involves a specific sequence: determining the sprocket size, estimating the center distance, calculating the required chain length in "pitches," and then recalculating the exact center distance. Search for "Machine Elements in Mechanical Design" 1. Pitch Diameter The pitch diameter is the theoretical circle that passes through the centers of the chain pins. For a sprocket with N teeth and a chain pitch of p , the diameter D is: D = p / sin(180 / N) *Note: The sine function uses Degrees, not Radians. 2. Center Distance Guidelines The Center Distance (C) is the distance between the shafts. While chains are flexible, sticking to standard design ranges ensures long life. Minimum: The sprockets must not touch. Ideally, C should be at least 30 to 50 times the pitch (30p - 50p). Maximum: L...

Understanding the Loads on a Chain In Part 1 , we looked at the types and advantages of chain drives. Now, we must tackle the math and physics behind them. Designing a chain drive isn't just about picking a chain that fits the sprocket. You must account for the Total Tensile Load . If you only calculate for the torque transmission, your chain will likely fail due to unseen forces like shock, inertia, or vibration. Search for "Standard Handbook of Chains" 1. Nominal Tensile Load The Nominal Tensile Load is the baseline force required to transmit power. However, this load is rarely static. It fluctuates in a cycle as the chain moves through the system: Tight Strand: As the chain engages the driven sprocket, tension is at its peak (transmitting the torque). Slack Strand: As it leaves the driver sprocket, tension drops significantly. This constant cycling between high and low tension creates Fatigue Loading . Over millions of cycles, ...