Hobbing a Helical Gear (Differential Method)

Robert Hermann Pfauter (RHP) invented the method of hobbing helical gears by adding a differential mechanism to the drivetrain of his machine. The slight retarding and advancement of the workpiece by the differential is THE SECRET... https://bit.ly/3onfQon
He 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 GE patent was in 1897, and his US patent in 1900. Advancements in CNC hobbing equipment came late compare 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-instrument gears, Barber-Coleman - American still being serviced by Bourn & Koch, Gleason-bevel gearing, LIEBHERR, Gould & Eberhardt, Fellows-Shaper...

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

REAL GEAR MAKERS LOOK HERE https://bit.ly/2ViRr9J
Use our online calculators to make gears: gear blanks, arbor sizes & gear measurement...
Use our online calculators to calculate change gears for your old hobber/shaper
Get a larger hobber from Gibbs Machinery https://bit.ly/3Ajv5Es
Get a small instrument hobber and tester from George Tahan https://bit.ly/3AknaXj
Get the Hob from Ashgear (talk with Brad Jerris) https://bit.ly/3fH58a4

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: https://amzn.to/3rkfoJT

Interesting Gear schematics can be found in Tony Freeth's 2012 research paper:
http://dlib.nyu.edu/awdl/isaw/isaw-pa...

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)
https://amzn.to/3hOwZXa

Jesse Ramsden (1735-1800) Science, Technology and Culture, 1700-1945
https://amzn.to/3wXfVTq

Sir Joseph Whitworth, A Pioneer of Mechanical Engineering"
https://amzn.to/3wQoz61
https://evolventdesign.com/blogs/hist...
British Patent Number 6850 from the year 1835 aka (GB183506850A)

Woodbury, Robert S, "History of the Gear-Cutting Machine"
https://amzn.to/3eCRsMO

Video Credits
The CT and PTM data that the AMRP have made publicly available can be found here http://www.antikythera-mechanism.gr/data

Gleason Corp - Pfauter Training Video - Encyclapedia/GE-EN Dictionary
https://www.gleason.com/en/encycloped...

Chris Maj - Helical Gearbox clip

Pfauter US Patent (1900)
https://patents.google.com/patent/US6...

NASA Reference Guide on Gearing
https://evolventdesign.com/blogs/hist...

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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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