[Video] Hobbing a Helical Gear (Differential Method)

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Robert Hermann Pfauter (RHP) invented the method of hobbing helical gears by adding a differential mechanism to the drivetrain of his machine. "The Secret" is the slight retarding and advancement of the workpiece by the differential

Pfauter made the hob head rotate on the vertical column of his machine for the helix angle – in concert with the differential – the hobber produces helical gears. With the formulas and setup schematics in the owners/operators manual the machine can cut right-hand and left-hand helical gears.

These advancements added to his hobbing machine's capabilities to make spur gears, sprockets, spline shafts, ratchets and worm gears making a differential equipped Pfauter a very Universal Machine Tool.

Timestamps:
0:00 Types of Gears
1:24 Gears and History
2:45 Pfauter
3:52 Modern Pfauter
5:57 Machine Setup
9:05 Pfauter Logo
10:36 Differential
12:09 Scallop Surface Finish
13:14 Wrap-up

Helical Gear Manufacturing Characteristics:

  • One hob can cut right-hand AND left-hand helical gears
  • At angles from about 7° to 45°
  • For tooth counts ranging from about 20 to the limits of the machine (at least 130T)

RHP's first German patent was in 1897, and his US patent in 1900. Advancements in CNC hobbing equipment came late compared to mills and lathes. In the early 1970's some of the drivetrain components were simplified with electric motors and rotary encoders. So any machine you buy prior to this date will be all mechanical.

There were many hobbing machine manufacturers making machines prior to 1970 and surprisingly there is a very active market for these machines. Some brands of interest: Pfauter (obviously), Mikron (for instrument gears), Barber-Coleman (American company, still being serviced by Bourn & Koch), Gleason (for bevel gearing), LIEBHERR, Gould & Eberhardt, and Fellows (for gear shaping)

If you have a mill, get a lathe. If you have a lathe, get a mill. If you have both, get a hobber!

The Pfauter (code name Jersey) used in this video is a RS00 Model, made in about 1950. Refurbished with all new bearings & seals. Nothing special, easy to source and commonly available. We spec'd bearings by Timken. Gear Oil Pump-resurfaced, bench checked and reinstalled. New stud post (scissor) for the differential gear cluster, new quadrant studs and hardware. Rebuilt operator panel to allow for more & modern pushbuttons. All new PLC and VFD's drive the machine, just a few dozen lines of ladder logic make it function safely

References:
Gears From The Greeks - Derek de Solla Price

Interesting Gear schematics can be found in Tony Freeth's 2012 research paper 

Pfauter - Hobbing, The engineer’s pocket book for Hobbing with Pfauter's Hob Cutter Catalog Julius Springer Approximately 1930 (In German If anyone knows the exact date please let me know) Pfauter - Hobbing, Volume 1, Springer-Verlag, 1976 (In German) 

Jesse Ramsden (1735-1800) Science, Technology and Culture, 1700-1945 

Sir Joseph Whitworth, "A Pioneer of Mechanical Engineering

Woodbury, Robert S, "History of the Gear-Cutting Machine

Video Credits:
The CT and PTM data that the AMRP have made publicly available can be found here 

Gleason Corp - Pfauter Training Video - Encyclopedia/GE-EN Dictionary

Chris Maj - Helical Gearbox clip

Pfauter US Patent (1900)

NASA Reference Guide on Gearing 

The history of gears is surprisingly interesting - the process of milling and hobbing gears plus the transmission of torque and movement all find a place here. We will open the "Secret Gear Case" to YT as well through this channel - a personal mission

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