For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
Figure 1: A heavy-duty roller chain drive provides positive engagement and high torque transmission for industrial applications.
Introduction to Chain Drives
Chain drives are the workhorses of industrial power transmission. They are used to transmit rotational motion and torque from one shaft to another with high efficiency and reliability.
In the hierarchy of mechanical design, chain drives occupy a unique middle ground: they offer the flexibility of a belt drive (allowing for large center distances) combined with the positive engagement of a gear drive (no slippage). This makes them ideal for applications ranging from slow-speed, high-torque conveyors to high-speed automotive camshafts.
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Advantages of Chain Drives
When compared to gears or belts, chain drives offer several distinct engineering advantages:
- Shaft Center Flexibility: Unlike gears, which require precise touching distances, chains can accommodate long shaft-center distances (typically up to 4 meters).
- Zero Slippage: Chains provide a positive drive ratio, making them superior to V-belts for timing applications.
- Lower Shaft Loads: Belts require significant initial tension to prevent slipping, which adds radial load to the bearings. Chains run on the "slack side" and "tight side" principle, requiring little to no pre-tension.
- Durability: Metal chains do not deteriorate with age, sunlight, oil, or grease in the way rubber belts do.
- Compact Design: A chain sprocket is often smaller than a belt pulley for the same torque transmission, saving space.
Design Limitations: The Chordal Action
No mechanical system is perfect. The most critical phenomenon to understand in chain design is Chordal Action (or the Polygonal Effect).
Figure 2: The "Chordal Action" occurs because the chain wraps the sprocket as a polygon, not a circle. This causes velocity ripple and vibration, especially with sprockets under 17 teeth.
Because a chain wraps around a sprocket as a series of straight links (forming a polygon rather than a perfect circle), the speed of the chain fluctuates slightly within a single revolution. This causes:
- Velocity variation (speed ripple).
- Vibration and noise.
- Impact loading on the sprocket teeth.
Design Tip: To minimize chordal action, always select a sprocket with a higher number of teeth. Generally, a minimum of 17 teeth on the smaller sprocket is recommended for smooth operation.
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Global Standards: ANSI vs. ISO
Standardization is critical for interchangeability. The two dominant standards in the world are ANSI (American National Standards Institute) and ISO (International Organization for Standardization).
1. British / ISO Standard Roller Chains
Covered by standards BS 228, ISO R606, and DIN 8187. These are common in Europe and parts of Asia.
| ISO/BS No. | Pitch (mm) | Roller Dia. (mm) | Width Between Inner Plates (mm) |
|---|---|---|---|
| 05B | 8.00 | 5.00 | 3.00 |
| 06B | 9.525 (3/8") | 6.35 | 5.72 |
| 08B | 12.70 (1/2") | 8.51 | 7.75 |
| 10B | 15.875 (5/8") | 10.16 | 9.65 |
| 12B | 19.05 (3/4") | 12.07 | 11.68 |
| 16B | 25.40 (1") | 15.88 | 17.02 |
Table 1: Standard dimensions for common ISO/British roller chains.
2. Understanding the Numbering System
The numbering logic is simple once understood. The digits relate directly to the pitch as a fraction of an inch.
| ANSI Standard (B29.1) - Based on 1/8" Pitch | ||
|---|---|---|
| ANSI Chain No. | Pitch Calculation | Decimal Pitch (inch) |
| No. 35 | 3/8" | 0.375" |
| No. 40 | 4/8" | 0.500" |
| No. 50 | 5/8" | 0.625" |
| No. 60 | 6/8" | 0.750" |
| No. 80 | 8/8" | 1.000" |
| No. 100 | 10/8" | 1.250" |
Table 2: Quick reference guide for ANSI chain numbering based on 1/8-inch pitch increments.
Next Step: Calculation
Now that we understand the types and standards, how do we calculate the required length and power rating?
Continue to Part 2:
Chain Drives Design: Load Analysis and Tension Factors (Part 2)
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