Gear Hobbing Cutters

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. SprocketsSprockets 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. 

How cryogenic hardening makes for stronger cutters

The process of cryogenic hardening has proven to deliver incredible results for metals. The same holds true for gear hobs as well. It’s possible to make stronger cutters through the application of cryogenic hardening. 

There are obvious benefits to be had in this industry. Gear manufacturers are well aware how costly their production processes are. The hobs are very likely their most costly part because they suffer the most wear and tear. 

They need to replace them constantly to ensure efficiency and reliability in the production processes. That’s because the hobs can suffer from tooth profile changes after extended use and that can have a direct impact on product quality.

Deep cryogenic treatment is rapidly becoming the preferred method to increase the durability and lifespan of gear hobs. 

Cryogenic hardening can increase the lifespan of gear hobs by up to five times. That significantly reduces the number of replacements that gear makers have to purchase each year, leading to a sizable reduction in their expenses.

The benefits of using cryogenic hardening on hobs and cutting tools is already well known. Companies that go for this treatment on their tools enjoy less downtime and reduced maintenance requirements. 

With deep cryogenic treatment, it’s possible to reduce the consumable tooling costs while also increasing the quality of products.

About CTP Cryogenics

Controlled Thermal Processing Cryogenics is one of the leaders in deep cryogenic processing. We use state-of-the-art equipment and our proprietary deep cryogenic treatment process to deliver exceptional results for our customers. 

The process is highly advanced and involves cooling the gear hobs down to temperatures below -300⁰F. 

It’s important to realize that the process isn’t as simple as dipping the gear hobs in a tub of cryogenic materials like liquid nitrogen and considering it a job well done. 

It’s a much more scientific process that can’t be performed without specialized machinery and computers. In our deep cryogenic hardening process, the materials are kept submerged in the liquid that can be around  −320°F for up to 24 hours.

This is done to alter the crystalline structure of the metal so that it becomes a more uniform and durable construct. 

The temperature of the metal is then gradually brought back up to room temperature in order to make the changes to the crystalline structure permanent.

Heat tempering is also an important part of the process for some metals. It’s done after the submersion part of the process is completed. 

This requires that the temperature be increased gradually to around +300°F. Heat tempering is necessary to ensure that any brittleness that could have been caused during the cryogenic treatment is reduced.

CTP Cryogenics has one of the most advanced processes for gear hobs that work on both HSS and carbide hobs. This allows us to improve the performance of these tools beyond what has ever been possible. 

If you’ve been looking for a cryogenic processing solution for gear hobs, reach out today for a free quote and our highly experienced team will reach out with all of the details that you need to get the job done.