Gears are utilized in a wide variety of machines. These rotating circular components have cut teeth or inserted teeth, in gear wheels for example, that mesh with another toothed part to transmit torque. The teeth on two meshing gears have the same shape. Gears make it possible to change the torque, speed, and direction of a power source. 

The earliest examples of gears can be traced back to the 4th century BC in China. They have been around for centuries and have contributed to significant industrial growth. Have you ever taken a moment to wonder just how these gears are made?

The process that’s now widely used to manufacture gears is called hobbing. The process is used to create spur and helical gears. This is a preferred process because hobbing is both quick and relatively inexpensive.

What is hobbing?

The machining process that’s used for gear cutting on a machine is called hobbing. Hobbing machines can be considered as a special kind of milling machine. The teeth of the gear are progressively cut into the base material through a series of cuts applied by a cutting tool called the hob. 

This is a relatively inexpensive way of making gears compared to other gear forming processes and also happens to be quite accurate. That’s why hobbing is typically used for manufacturing gears. 

Hobbing machines have two skew spindles, one that’s mounted with a workpiece and the other with the hob. The angle between the workpiece and hob’s spindle depends on the type of gear being produced. 

These two shafts are then rotated at a proportional ratio that determine the number of teeth on the workpiece. The hob is fed up into the workpiece until the desired tooth depth has been achieved. 

Hobbing machines are also called hobbers and they’re available in a variety of sizes. These are fully automated machines that can be used to produce a wide range of products such as small instrument gears to industrial sized gears. 

Types of gears made by hobbing

1. Helical gears – Helical gears are often called dry fixed gears and they offer a certain level of refinement. That’s made possible because the leading edges of the teeth are not parallel to the axis of rotation. Since the gear is curved, the tooth shape makes a segment of a helix. They are the preferred choice for machines that require high speeds or high loading.

2. Sprockets – Sprockets are profiled wheels with teeth or cogs. They can mesh with a track or chain that’s passing over it. They’re different from conventional gears because the sprockets aren’t meshed together directly.Sprockets are most commonly used in bicycles, motorcycles, and cars as well as other machines that need to transmit rotary motion between two shafts.

3. Involute gears – Involute gears are among the most popular of gear solutions today as the tooth profile of involute gears enables smooth transmission of power with minimal speed or torque.The gears that are used in higher-strength applications are mostly helical involute gears in which the spirals of the teeth are of different hands with the gears rotating in an opposite direction.

4. Ratchets – Ratchets enable continuous linear or rotary motion in one direction only. They’re utilized in applications where it’s absolutely crucial to prevent motion in the opposite direction. A ratchet has a round gear with teeth and a pivoting, spring-loaded finger that’s called a pawl. They’re used in tools, slacklines, handcuffs, cable ties, and more.

5. Spur gears – Spur gears can also be made through hobbing. They’re the simplest type of gear that consist of a cylinder or disk with radially projecting teeth. These gears are only able to mesh together properly if they’re fitted to parallel shafts.The tooth loads don’t create any axial thrust. These are great for use at moderate speeds but can be very noisy at high speeds. They’re commonly used in machines to increase or decrease the speed.

6. Splines  – Mechanical splines are the teeth on a drive shaft that mesh with grooves for torque transfer while maintaining the angular correspondence between them. Their most common use is in the drive shafts of vehicles that use them for the transmission of torque and rotation.

7. Worm gears  – A worm in this particular instance is a gear that’s in the form of a screw. They’re also called an “endless screw” and are used to reduce rotational speed or transmit higher torque. Their biggest advantage is that they can transfer motion in 90 degrees.The worm in a worm gear can have single or multiple starts and with each full 360 degree turn of a single start, the worm advances the gear by one tooth. They’re used as the tuning mechanism for musical instruments like guitars, in roller cotton gins, and other machines.

What is a gear hobbing cutter?

A hob is the cutting tool that’s used by the hobber to cut the teeth into the blank workpiece. Hobs are cylindrical in shape and have helical cutting teeth that feature grooves which run the length of the hob. 

These teeth help in cutting and chip removal. Special hobs are also designed for certain products like sprocket gears. 

The teeth on the hob have a cross-sectional shape that’s almost identical to the teeth of a rack gear that would be used with the final product. 

The slight changes to the cross-sectional shape are only required for cutting purposes but every single hob tooth is relieved on the back side in order to reduce friction.

Hobs generally tend to be single-thread hobs but it’s not uncommon for double and triple-thread hobs to be used in order to increase the rate of production. The only problem with them is that they may not be as accurate as single-thread hobs. 

General purpose and custom made hobs are both utilized depending on the nature of the project. The hobs that are made custom for a specific job are different since they are used to make gears with modified tooth profiles.