A Short History of Gears and Where Gear Manufacturing Is Today

 

CNC Gear Hobbing Machine

 

Gears were a logical continuation of the invention of the wheel. That gears are called the biggest invention after the wheel is not unthinkable. In any case, we can't live a normal day in our lives without gears: without gears no production, no energy, and no transport. The use of gears is so obvious that we never dwell on where they come from. In this article, out of respect for the gear, we will detail the interesting history.

Gears are such a common simple machine that it's hard to think there was ever a time before they were used. But just like the wheel or any other man-made invention, gears had a starting point and a course of evolution over thousands of years that have led to their current state today.

 

Gears Are Actually a Natural Product

baby-lantaarnachtigeBut were the ancient Greeks really the inventors/ Research biologists at the University of Cambridge are certain that the ancient Greeks were not the first. The three-millimeters small bug Issus coleopterans, a lantern bearer like those in Europe and North Africa, uses this mechanism already for millions of years. The gear is not a human invention of the ancient Greeks, but a mechanism that arose through evolution in nature.

Nymphs of the insect have an ingenious system of gears that causes their rear legs “click” together and at the same time run away and then jump forward. Using electron microscopy and high-speed cameras biologists captured the precise operation of the insects' mechanisms. It is known so far as the first working gear system from nature.

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CNC 5 Axis High Speed Gear Hobbing Machine

 

First gear was developed

It's hard to say when the first gear was developed, but some of our earliest records point back to around 2700 BCE, with gears featuring in a device called the Chinese South-Pointing Chariot. This chariot featured a gear that would automatically turn a directional arrow so it always pointed south, no matter which way the chariot itself turned. It was one of the earliest ways to gauge cardinal directions without the use of magnets.

Gears were also formally mentioned by Aristotle in some of his writings around 400 BCE. He described gears as capable of reversing the direction of momentum, and we've found artifacts dating back almost this far with gears as central components, such as in wheels and rudimentary clocks. Gears also featured prominently in inventive sketches by Leonardo da Vinci, circa 1500.

By the 1600s, scientists and engineers were figuring out mathematical concepts like velocity ratios and involute curves, allowing them to use gears for more complex and more heavy-duty tasks, but it wasn't until the 1800s when the first form cutters and gear hobbing machines emerged, allowing gears to be mass-produced and refined in terms of form and performance.

The next major step forward was in 1897 when Herman Pfauter invented the machine that could cut both traditional “spur” gears and helical gears, driving production further forward. Over the next hundred years or so, the development of NC hobbing machines and full 6-axis machines would start to perfect how we design, cut, and manufacture gears.

 

Today Gear Manufacturing

Today, gear manufacturers primarily use CNC machines to cut gears from blanks, and our level of precision is driven by sophisticated design software and advanced engineering theories. Modern gears are exceptional pieces of work, capable of lasting centuries (or longer, if cared for properly), and technology continues to advance to bring us better ways of producing gears.

 

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Difference Between Gear Milling and Gear Hobbing

 

CNC Gear Hobbing Machine

 

Gear is a vital component for rotating machines, with teeth mesh with another toothed part to transmit torque. How gears are made? Other than casting, forging, CNC machining can be applied to achieve the final shapes, dimensions, and surface finish of a gear. Here we introduce and compare two gear manufacturing methods – gear milling vs gear hobbing, what are the differences between them?

 

What is Gear Milling?

 

Gear milling is a common CNC milling operation and gear-cutting process of creating a gear. It can be operated either after or instead of forming processes including casting, forging, and extruding. Gears are usually made from metal, plastic, and wood. Many metal and plastic gears made by die-casting, injection molding, or additive manufacturing may not require cutting. For coarse-pitch gears, the generative gear milling technology can improve efficiency, expand the pitch capacity of the machine, reduce cutter cost, and may decrease the machining times.

 

What Cutter Used in Gear Milling?

 

The gear can be cut on a milling machine or jig grinder utilizing a gear cutter and indexing head or rotary table, the quantity of gear cutter is determined by tooth count of the gear required. Various types of cutters can be used for producing gears, for example, the rack shaper, with six to twelve teeth, straight and move in a direction tangent to the gear. The cutter has to move back to the beginning position for the new round cut.

 

What is Gear Hobbing?

 

Gear hobbing is also a gear manufacturing method to cut teeth into the blank with a hob like an index hob and master hob on CNC gear hobbing machines. The hob and gear blank rotate at the same time in a mesh and cut the teeth by continuous cut, the rotating hob is fed inward until achieving proper depth, then work for the entire gear. Gear hobbing is a great choice for medium to high volume production runs. The hobbing features for gears including straight, helical, straight bevel, face, crowned, worm, and chamfering.

 

How to differentiate gear hobbing and gear milling?

 

1. The way gear teeth are produced

 

In gear milling, a single tooth spacing or gap between gear teeth will be created by a rotating multi-edge cutter at a time, the cross-section of generated teeth is similar to that of the cutter. In gear hobbing, the gear teeth are progressively produced by a series of cuts with a hob. So the hob cuts several gaps simultaneously.

 

Hobbing Machine

 

2. Cutter

 

Gear milling uses a rotating form cutter, when each tooth space is cut, the cutter will return to the starting point and gear blanks are indexed for next cutting process; gear hobbing uses a helical hob cutter, the hob and the workpiece are both rotating constantly when the hob is fed across the face width of the blank.

 

3. The number of teeth cut in one time

 

Each cutter in gear milling is designed to cut a range of tooth numbers, while in gear hobbing, both the hob and gear blank rotate continuously as in two gears meshing until all teeth are cut.

 

4. Price of tool

 

Generally, the gear milling cutting tool is cheaper than that of hobbing, but the productivity of gear hobbing may be higher.

 

5. Application

 

Gear hobbing is more often used for high production runs, and gear milling is a low production process.

 

6. Others

 

– Gear milling requires deburring

– Gear milling is often used when other generating processes are unavailable.

 

If you’re eager to learn more about the gear hobbing machine, or if you have an order you’re ready to place, contact GEEPRO today! We’ll have a quote back to you in less than 24 hours.