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The art of gear cutting: Differences between hobbing, skiving and power skiving

Guide for production engineers: When to use which gearing technology for optimum results by Oliver Hagenlocher & Jörg Lohmann

by Oliver Hagenlocher 24. July 2025
24. July 2025
165

In modern manufacturing , there are several processes for producing tooth profiles. Three frequently used – yet often confused – important technologies that are often confused are hobbing, skiving and power skiving. Each method has its own applications,  advantages and limitations. Understanding the key differences is crucial in selecting the right technology for each job. 

Hobbing – the standard technology for external gears

Hobbing is the most established and widely used method for producing external gears. In this process, the rotational axis of the tool and the workpiece typically intersect at an angle of between 45° and 135°., meaning the axes are crossed. 

Technological basics:

  1. The hob resembles a worm with axial flutes that creates cutting edges, known as cleats. These are relief-ground to produce a clearance angle. 
  2. Cutting speeds are based on the hob diameter and its cutting speed. 
  3. The feed rate is measured in mm per workpiece revolution. 
  4. In gear technology, the hob behaves like a worm gear with a 90° axis angle. 

Area of application:

  • Primarily for soft machining of external gears 
  • Occasionally used for hard machining of small modules (less than 1) , though rarely 
  • Suitable for both pre-machining and final gear cutting 
  • Applicable for straight and helical gearing 

Watch in this video: Industrial hobbing of an external gear with coolant supply in an EMAG K 160 CNC gear cutting machine.

Bottom line:

Hobbing is the first choice for mostexternal gears in the soft state, provided there are no interfering contours or cutter run-out constrainsts exist. It’s widely accepted among manufacturers and is considered the standard process. High machining speeds can be achieved using multi-start milling cutters, high studs and modern tool materials and coatings. 

More on the Technology Hobbing on our website >>

 

Skiving – precision finishing for hardened tooth profiles

Skiving is a finishing process used on hardened gears  to correct quality loss from hardening and improve surface quality. 

Technological basics:

  1. Based on the same principles as hobbing. 
  2. The key difference: material is only removed from the tooth flanks. 
  3. Pre-milling creates a special undercut profile in the tooth root, called a protuberance, to allow tooth flank access for subsequent machining.  
  4. High-precision sensors are required for exact skiving cutter positioning. 

Area of application:

  • Exclusively for hard machining of external gears 
  • After hobbing, gears typically achieve ISO 1328 quality 6-8. 
  • Distortation may reduce quality by 1-2 grades after hardening. 
  • Skiving can restore quality back to ISO 1328 class 6-7. 
  • The surface finish also improves significantly (Ra approx. 0.5, Rz approx. 2.5). 

Bottom line:

Skiving is ideal when high-quality hardened gears (class 6-7) are required. Compared to grinding, it offers benefits like lower tool costs, faster cycle times (especially on small gears and pinions) and the ability to perform both soft and hard machining on the same machine. However, it does not achieve the same level of precision as grinding. 

Detailed view of a skiving process during the machining of a steering pinion in a K 160 from EMAG

Skiving process of a steering pinion in an EMAG K 160 CNC gear cutting machine.

 

Power skiving – Flexible for internal and external gears

Power skiving is a versatile technology suitable for both internal and external gear profiles, with key benefits for machining Challenging geometries, such as profiles adjacent to shoulders or interfering contours. 

Technological basics:

  1. Defined by an axis crossing angle between  10° and 25° 
  2. Due to its kinematics, very high spindle speeds may be required 
  3. Performed through multiple axial passes (multi-cut process). 
  4. The feed rate is in mm per workpiece revolution. 
  5. The cutting speed results from the difference in tool and workpiece speed vectors. 
  6. In gear technology, the process corresponds to a skewed-axis helical gearbox. 

Area of application:

  • For soft machining of internal and external gears 
  • Especially useful when machining near  a plane shoulder or other interfering contour 
  • Allows pre-turning and tooth cutting in a single setup 
  • Suitable for both straight and helical gears 

Watch in this video: The power skiving process in the work area of an EMAG VSC 400 PS. The machine specializes in the precision machining of internal and external gears.

Bottom line:

Power skiving is ideal for smaller batch sizes and flexible production. It excels at cutting internal gears  and tooth profiles “against collar”, where other processes reach their limits. The ability to combine turning and gear cutting in a single setup saves production steps. However, it requires stable clamping, high tool quality and high motor speeds. During power skiving, the kinematics sometimes result in highly negative rake angles. 

More on the Technology Power skiving on our website >>

 

Direct comparison of technologies

Summary of the differences and areas of application: 

Procedure  Field of application  Particularly advantageous for  Frequency in industrial use 
Hobbing (Hobbing)  External toothing (soft)  all splines  Very high 
Skiving (skiving)  External gearing (hard)  hardened tooth profiles with ISO 1328 quality 6-7  high 
Power skiving (power skiving)  Tooth profiles (internal and external, soft)  smaller batches, flexible production, internal gear cutting and tooth profiles “against interfering contours”  medium 
Schematic representation of four gear machining processes: gear planing, hobbing, shaping, and skiving with corresponding feed and speed parameters.

Four gear machining processes compared: gear planing, gear hobbing, gear shaping, and gear skiving. The schematic diagram illustrates the tool, workpiece, and relevant parameters such as cutting speed (vc) and feed rates (fa, fr, fw).

 

Conclusion

Choosing the right gear cutting method depends on various factors, including 

  • Type of tooth profiles (internal or external) 
  • Material condition (soft or hardened) 
  • Required quality and surface finish 
  • Batch size and flexibility requirements 
  • Geometric features (e.g. tooth profiles against collar) 

Gear hobbing remains the standard for most soft-machined externals gears. Skiving is a cost-efficient alternative to grinding for hardened precision gears. Power skiving is the ideal solution for internal gears or geometrically complex parts, especially when flexibility and efficiency are needed. 

Thanks to ongoing innovations by companies like EMAG, gear cutting technologies continue to become faster, more precise and more economical – delivering significant performance advantages for modern transmissions. 

CNC machininggear cutting / gear hobbingGear hobbinggear manufacturingGear technologyManufacturing Technologyplaningpower skivingSkiving
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Oliver Hagenlocher

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