Chain Drives Design: Fundamentals, Advantages, and Standards (Part 1)

In automation design, the choice between a Stepper Motor and a Servo Motor is often decided by budget. But looking at the price tag alone is a mistake that leads to machine failure. Steppers are excellent for holding loads stationary (high holding torque). Servos are kings of high-speed motion. If you choose a stepper for a high-speed application, it will lose torque and "miss steps." If you choose a servo for a simple low-speed application, you have wasted $500. This guide explains the physics behind the choice. Table of Contents 1. Open Loop vs. Closed Loop (The Risk) 2. The Torque Curve: Speed Kills Steppers 3. Inertia Mismatch 4. Selection Summary Advertisement 1. Open Loop vs. Closed Loop (The Risk) The biggest difference is not the motor itself, but how it is controlled. Figure 1: Steppers run "blind" (Open Loop). Servos use an encoder to verify position (Closed Loop). ...

Chain Drives Design: Fundamentals, Advantages, and Standards (Part 1)

Photorealistic industrial roller chain drive system in a factory setting

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).

Engineering diagram illustrating the polygonal effect and velocity fluctuation in a chain drive

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.

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.

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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)

References

Chain Guide (Recommended Resource)

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