#003 Belts & Chains
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Definition

A Belt is a loop of flexible material, often rubber or leather, used to transmit rotational power from one round shaft to another. Belts may have a twist between the pulleys, and the path can be guided around corners.

Belts are very much descended from the belts that hold up pants. For centuries, leather was the strongest flexible material available.

Belt drive power delivery mechanism, machine shop, Hagley Museum
Flat Belts are the simplest type of belt, typically leather, rubber, or cloth. They typically need to be quite wide to provide enough friction.
Green Conveyor Belt
Conveyor Belts are a type of flat belt, wide enough to carry packages or raw materials such ar corn or coal.
Round Belt
Round Belts is a loop of a tube, typically of soft rubber. "O-rings" can be used for smaller diameters, while longer lengths can be made from tubing that is connected with an internal plug. These are primarily used for low speed and low torque uses, as the soft rubber tends to stretch.
Public domain
Timing Belt
Timing or Toothed Belts have rubber "teeth" that fit into sprockets or hubs. The teeth can deliver very large force without slipping. The teeth also keeping both shafts "indexed" together, as a gear or chain does, which is useful for being confident on how much the wheels have turned.
Public Domain
V Belt
V Belts have a shape sort of like a V, which gives more surface area against the pulleys, as well as keeping the belt from wandering off the pulley. They are typically much more effective than flat belts. The V belt gets pulled into the pulley's groove as the load increases, increasing friction, which improves torque transmission.
Link Belts
Link Belts are a type of V belt made from individual links that make adjustments or fixes easier. There are reports that they can be quieter.
Public Domain
Link Belts
Multi Groove or "Serpentine" Belts have a flat design with multiple ribs that give a large frictional surface area for power transmission in a small space. They are commonly used in cars to drive alternators, fans, water pumps, AC compressors and power steering systems in modern engines. They are often made of synthetic rubber, with fiber reinforcements and can be extremely strong.
Public Domain
Two different sizes of roller chain for motorcycles and bicycles
Chain offer several advantages over gears and belts. The common "Roller Chain", seen on bicycles, is made of a series of short cylindrical rollers held together by side links. It is driven by a toothed wheel called a sprocket. It is a simple, reliable, and efficient means of power transmission. Leonardo da Vinci sketched a chain with a roller bearing in the 1500's. James Fussell patented a roller chain in England in 1880.

Key Facts

  • Toothed Belts are complex cast parts that essentially cannot be fixed by the end user. Because they do not stretch and cannot be unlinked like a chain, you must design around them. For example, removing the rear tire on a belt-driven bicycle can be complex.
  • Belts or chains require tension that is neither too tight (causing stretching) or too loose (reducing power delivery or even skipping teeth). Belt and Chain tensioners or idler wheels are used to take up slack.
  • Chains can be shortened or lengthened with a chain tool that pushes the internal pins out. Chains sometimes have a "Master Link" for quick release of a chain.
  • Belts versus Chains is a common design question with different answers depending on the specific design. Metal and plastic chains, belts, and toothed belts have different weight, breaking strength, wear, and responsiveness.

Engineering Rules of Thumb

  • Keep in mind the ability to alter the length during design, for example quickly adding or removing links in a chain. Toothed belts are very powerful, but typically must be ordered, causing delays, and come in standard sizes.
  • You might consider starting with chain and replacing with a toothed belt when the design becomes stable.
  • Chains and toothed belts might always seem like the best solution, but it is often important that a belt should slip! Many machines will happily rip them selves apart in a "jam" if the motor is directly connected to all parts. This is also important when working around human bodies, which must be protected. In some cases, designing a clear weak spot protects the machine by having it break in a predictable, easily fixed, location. For reference, this Home Machinist Lathe discussion.
  • Toothed belt efficiency can be the highest, but well maintained chains and V belts can all be quite close. If you are designing an automobile engine, you care about long term wear. If you are making a FRC robot, you probably care about speed to prototype and strength.
  • Belts are typically run at a much higher tension to avoid skipping. However, high tension can wear out bearings or bend aluminum frames if not supported.

View in 3D

iPhone Augmented Reality Viewer

Display

This model displays 4 samples of Belts and Chains. A rubber tube belt in upper left. A toothed or timing belt in upper right. A chain in lower right. A Link Belt in lower right, on a "Pulley Stack", which allows adjustable gear ratios.

Belts & Chains display in Mechanical Library
Belts & Chains display in Mechanical Library
Source: mechanical-library.org
Video of Belts & Chains display in Mechanical Library
Source: mechanical-library.org
Mechanical Library Belt & Chains model
Mechanical Library Belt & Chains model
Source: mechanical-library.org

Images

Children working on textile mill powered by a flat leather belt.
"Grease monkeys" were children who greased the large rotating axles which were used to transfer power from one centralized steam engine to all of the machines on the factory floor. The name came from working covered in grease and crawling in the tight spaces in the ceilings. New York State law still prohibits minors from "Cleaning, oiling, wiping or adjusting belts to machinery".
Evans Friction Cone, Cone Ring Transmission
Evans Friction Cone, Cone Ring Transmission, variable speed mechanism, machine shop, Hagley Museum
Supercharger drive belt in a dragster
Supercharger drive belt in a dragster
Toothed Belt on a bicycle
Toothed Belt on a bicycle
Diagram showing parts of Roller Chain
Parts of Roller Chain 1. Outer plate 2. Inner plate 3. Bolt 4. Sleeve 5. Roller
Gritzner Sewing Machine
Gritzner Sewing Machine, not pink-ish leather round belt.

Videos

3D Printing

Mechanism in Legos

Legos have long supported belts and chains in their models.

History

Early gears were made from wood with cylindrical pegs for cogs and were often lubricated with grease from animal fat. Gears were used to change the rotational speed from water wheels or wind mills to power pumps or grain mills. The speed of a horse was typically too slow to use, so wooden gears increased the speed.

Sketch of roller chain, Leonardo da Vinci, Codex Atlanticus
Sketch of roller chain, Leonardo da Vinci, Codex Atlanticus
Source: Namazu-tron, Public domain, via Wikimedia Commons
Illustration of a roller chain and sprocket wheels
Chain in the final drive of a Sentinel steam wagon, 1911.
Model: V05 Adjustable Belt Drive for Parallel Axis Pulleys
In this model, both input and output rotational motions are about parallel, vertical axes. The pulleys are connected with a belt drive and the plane of the input and output pulleys can be slightly different. The transfer of motion is accomplished by using a horizontal axel with two smaller pulleys. All four pulley wheels are crowned to produce self alignment of the belt on the pulleys.

Reconstructing the Library Display

The Mechanical Library Gear Reduction display is composed of

  • Custom Components
    • (1) Custom Laser-cut 1/2" plywood panel (400mm x 400mm)
    • (9) Custom Laser-cut 3/16" Acrylic Gears
    • (20) Custom Laser-cut 1/4" small Acrylic Gears
    • (10) Custom Laser-cut 1/4" clear Acrylic Supports
    • (1) Custom 3D printed motor mount
    • Contact us for details and files

Research