Fellows 20-4 CNC Gear Shaping Machine

$150,000 – $400,000 (new CNC); used units $30,000 – $100,000 Updated 2026-03-17

Key Specifications

Maximum Workpiece Diameter

500 mm (19.7 in)

Maximum Module

Maximum Face Width

75 mm (3 in)

Cutter Diameter Range

76 – 203 mm (3–8 in)

Stroke Rate

Up to 1,500 strokes/min

CNC Axes

4 (X, Y, C workpiece, B cutter)

Overview

The Fellows 20-4 is a CNC gear shaping machine from Fellows Corporation (now part of the Roper Technologies portfolio, with machines serviced through various gear machine specialists). Gear shaping is the process used for cutting internal gears, cluster gears, blind-shoulder gears, and other configurations that hobbing machines cannot reach. The Fellows 20-4 accommodates workpieces up to 500 mm in diameter with module to 4, enabling internal ring gear production for planetary drives, automotive automatic transmissions, and aerospace gearboxes. The CNC version of the 20-4 features programmable stroke length, helix angle, spindle speed, and cutter RPM, enabling flexible programming of different gear geometries without manual adjustments. The cutter reciprocates vertically while the workpiece and cutter rotate in coordinated motion to generate the gear tooth profile. Fellows gear shapers remain widely used in production environments for internal gear manufacture because no alternative process (hobbing, broaching) easily cuts internal helical gears.

Full Specifications

Parameter	Value
Maximum Workpiece Diameter	500 mm (19.7 in)
Maximum Module	4
Maximum Face Width	75 mm (3 in)
Cutter Diameter Range	76 – 203 mm (3–8 in)
Stroke Rate	Up to 1,500 strokes/min
CNC Axes	4 (X, Y, C workpiece, B cutter)
Helix Angle	Up to 45°
Gear Quality	AGMA 9-10
Control	CNC (Fanuc or Siemens)
Capability	Internal and external gears, splines

Strengths & Limitations

Strengths

Only practical CNC process for internal helical gears used in automatic transmissions
Cuts cluster gears and shoulder-adjacent gears that hobbing cannot reach
CNC version enables rapid reprogramming for different gear families
Fellows equipment has very long service life — well-maintained machines last decades
Wide application range: internal, external, splines, and sector gears

Limitations

Slower cycle time than hobbing for external spur gears
75 mm maximum face width limits to thinner gears
Production of new Fellows CNC shapers is now limited — support mainly through rebuild specialists
Requires specialized cutter grinding to maintain shaper cutter geometry

Best For

Automotive transmission shops producing internal ring gears for planetary sets Aerospace gearbox manufacturers cutting internal helical gears Industrial gearbox producers making cluster gear assemblies Job shops specializing in gear cutting for defense and aerospace applications

Frequently Asked Questions

01 What is gear shaping and how does it differ from hobbing?

Gear shaping uses a reciprocating pinion-shaped cutter that rotates in synchrony with the workpiece to generate the gear tooth profile. Unlike hobbing (continuous rotary), shaping can cut internal gears, blind-shoulder gears, and cluster gears because the cutter moves vertically and fits inside bore openings. Hobbing is faster for external gears but cannot cut internal gears.

02 Are new Fellows gear shapers still manufactured?

Fellows as a standalone brand no longer manufactures new machines. The legacy machine base is supported by rebuild and parts specialists. The gear shaping process is also offered by Mitsubishi (SH series), Gleason (Genesis 130SH), and Lorenz/Klingelnberg machines.

03 What gear quality does shaping achieve?

CNC gear shaping achieves AGMA 9-10 quality (DIN 5-6), suitable for automotive and industrial gearboxes. Grinding is required for AGMA 11-12 precision in high-speed or precision applications.