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Dr. Hermann J. Stadtfeld

Dr. Hermann J. Stadtfeld received in 1978 his B.S. and in 1982 his M.S. in mechanical engineering at the Technical University in Aachen, Germany; upon receiving his Doctorate, he remained as a research scientist at the University's Machine Tool Laboratory. In 1987, he accepted the position of head of engineering and R&D of the Bevel Gear Machine Tool Division of Oerlikon Buehrle AG in Zurich and, in 1992, returned to academia as visiting professor at the Rochester Institute of Technology. Dr. Stadtfeld returned to the commercial workplace in 1994 — joining The Gleason Works — also in Rochester — first as director of R&D, and, in 1996, as vice president R&D. During a three-year hiatus (2002-2005) from Gleason, he established a gear research company in Germany while simultaneously accepting a professorship to teach gear technology courses at the University of Ilmenau. Stadtfeld subsequently returned to the Gleason Corporation in 2005, where he currently holds the position of vice president, bevel gear technology and R&D. A prolific author (and frequent contributor to Gear Technology), Dr. Stadtfeld has published more than 200 technical papers and 10 books on bevel gear technology; he also controls more than 50 international patents on gear design, gear process, tools and machinery.

Articles by Dr. Hermann J. Stadtfeld

TECHNICAL ARTICLES | 2024-07-23

Bevel Gear Speed Increasers

For cylindrical gears, speed-increasing transmission stages are well known, and regarding profile shift, preferred pressure angles, and helix angles a set of rules applies, which is not much different from the rules for speed reducers. It is important to acknowledge that basically, a speed increaser has to be designed just like a speed reducer, but then the gear with the lower number of teeth is the output. Of course, the torque and the speed of the gear with the lower number of teeth (output) and the gear with the higher number of teeth (input) must be the same as if this transmission was used as a speed reducer. In the case of straight bevel gears, spiral bevel gears, and hypoid gears the same rules apply with some additions. Spiral bevel gears have many applications as speed increasers.  

FEATURE ARTICLES | 2023-12-11

The “Differential Difference” in E-Drives

Gleason's Coniflex® Pro Design and Manufacturing System for producing stronger, quieter, and more reliable e-drive differential gears in high volumes, for automotive, truck, bus and off-highway transmissions. It‘s the differential difference!

TECHNICAL ARTICLES | 2023-04-14

Conjugate Gears

The conjugacy of meshing gears is one of the most important attributes of gears because it ensures a constant velocity ratio that gives smooth, uniform transmission of motion and torque. Some of the world’s greatest gear theoreticians like Earle Buckingham, Wells Coleman, and John Colbourne laid the foundation for understanding conjugacy. Their teachings and interpretations of the law of gearing have been used by generations of gear engineers to design and manufacture gear transmissions for almost everything that is mechanically actuated. 

TECHNICAL ARTICLES | 2022-06-27

Double Differential for Electric Vehicle and Hybrid Transmissions — Sophisticated Simplicity

The fascination of the automotive differential has led to the idea to build a second differential unit around a first center unit. Both units have the same axes around which they rotate with different speeds. The potential of double differentials as ultrahigh reduction speed reducers is significant. Only the tooth-count of the gears in the outer differential unit must be changed in order to achieve ratios between 5 and 80 without a noticeable change of the transmission size.

TECHNICAL ARTICLES | 2018-08-01

UNIMILL for Prototype and Small-Batch Bevel Gear Manufacturing

UNIMILL is a milling method for the manufacture of prototype bevel gears using end mills or disk cutters.
ASK THE EXPERT | 2017-03-01

Universal Hobs

Another expert takes a crack at a previously answered question about double-helical gears and universal hobs.
TECHNICAL ARTICLES | 2016-01-01

The Importance of Profile Shift, Root Angle Correction and Cutter Head Tilt

Chapter 2, Continued In the previous sections, development of conjugate, face milled as well as face hobbed bevel gearsets - including the application of profile and length crowning - was demonstrated. It was mentioned during that demonstration that in order to optimize the common surface area, where pinion and gear flanks have meshing contact (common flank working area), a profile shift must be introduced. This concluding section of chapter 2 explains the principle of profile shift; i.e. - how it is applied to bevel and hypoid gears and then expands on profile side shift, and the frequently used root angle correction which - from its gear theoretical understanding - is a variable profile shift that changes the shift factor along the face width. The end of this section elaborates on five different possibilities to tilt the face cutter head relative to the generating gear, in order to achieve interesting effects on the bevel gear flank form. This installment concludes chapter 2 of the Bevel Gear Technology book that lays the foundation of the following chapters, some of which also will be covered in this series.
TECHNICAL ARTICLES | 2015-11-01

Development of Usable Bevel Gearset with Length and Profile Crowning

In the previous sections, the development of conjugate bevel gearsets via hand calculations was demonstrated. The goal of this exercise was to encourage the reader to gain a basic understanding of the theory of bevel gears. This knowledge will help gear engineers to better judge bevel gear design and their manufacturing methods. In order to make the basis of this learning experience even more realistic, this chapter will convert a conjugate bevel gearset into a gearset that is suitable in a real-world application. Length and profile crowning will be applied to the conjugate flank surfaces. Just as in the previous chapter, all computations are demonstrated as manual hand calculations. This also shows that bevel gear theory is not as complicated as commonly assumed.
TECHNICAL ARTICLES | 2015-09-01

Development of a Face Hobbed Spiral Bevel Gearset

This article is the fourth installment in Gear Technology's series of excerpts from Dr. Hermann J. Stadtfeld's book, Gleason Bevel Gear Technology. The first three excerpts can be found in our June, July and August 2015 issues. In the previous chapter, we demonstrated the development of a face-milled spiral bevel gearset. In this section, an analogue face-hobbed bevel gearset is derived.
TECHNICAL ARTICLES | 2015-08-01

Gear Mathematics for Bevel & Hypoid Gears

The calculation begins with the computation of the ring gear blank data. The geometrically relevant parameters are shown in Figure 1. The position of the teeth relative to the blank coordinate system of a bevel gear blank is satisfactorily defined with...
TECHNICAL ARTICLES | 2015-07-01

The Basics of Gear Theory, Part 2

The first part of this publication series covered the general basics of involute gearing and applied the generating principle of cylindrical gears analogous to angular gear axis arrangements the kinematic coupling conditions between the two mating members have been postulated in three rules. Entering the world of bevel gears also required to dwell somewhat on the definition of conjugacy. The second part is devoted to the different generating gears and the chain of kinematic relationships between the gear - gear generator - pinion generator and pinion.
TECHNICAL ARTICLES | 2015-06-01

The Basics of Gear Theory

Beginning with our June Issue, Gear Technology is pleased to present a series of full-length chapters excerpted from Dr. Hermann J. Stadtfeld’s latest scholarly — yet practical — contribution to the gear industry — Gleason Bevel Gear Technology. Released in March, 2014 the book boasts 365 figures intended to add graphic support of a better understanding and easier recollection of the covered material.
ASK THE EXPERT | 2014-08-01

Importance of Contact Pattern in Assembly of Bevel vs Cylindrical Gears

Why is there so much emphasis on the tooth contact pattern for bevel gears in the assembled condition and not so for cylindrical gears, etc?
TECHNICAL ARTICLES | 2014-01-01

Power Skiving of Cylindrical Gears on Different Machine Platforms

It has long been known that the skiving process for machining internal gears is multiple times faster than shaping, and more flexible than broaching, due to skiving's continuous chip removal capability. However, skiving has always presented a challenge to machines and tools. With the relatively low dynamic stiffness in the gear trains of mechanical machines, as well as the fast wear of uncoated cutters, skiving of cylindrical gears never achieved acceptance in shaping or hobbing, until recently.
TECHNICAL ARTICLES | 2012-10-01

Differential Gears

What are the manufacturing methods used to make bevel gears used in automotive differentials?
TECHNICAL ARTICLES | 2011-05-01

Beveloid & Hypoloid Gears

Beveloids are helical gears with nonparallel shafts, with shaft angles generally between 5 degrees and 15 degrees. This is part VI in the Tribology Aspects in Angular Transmission Systems Series
TECHNICAL ARTICLES | 2008-08-01

Guidelines for Modern Bevel Gear Grinding

This paper acknowledges the wide variety of manufacturing processes--especially in grinding--utlized in the production of bevel gears...
TECHNICAL ARTICLES | 2007-09-01

The New Freedoms: Bevel Blades

Today, because of reduced cost of coatings and quicker turnaround times, the idea of all-around coating on three-face-sharpened blades is again economically viable, allowing manufacturers greater freedoms in cutting blade parameters, including three-face-sharpened and even four-face-sharpened blades.
TECHNICAL ARTICLES | 2007-08-01

Bevel Gears: Optimal High Speed Cutting

This article presents a summary of all factors that contribute to efficient and economical high-speed cutting of bevel and hypoid gears.
TECHNICAL ARTICLES | 2005-09-01

What to Know About Bevel Gear Grinding

Guidelines are insurance against mistakes in the often detailed work of gear manufacturing. Gear engineers, after all, can't know all the steps for all the processes used in their factories.
TECHNICAL ARTICLES | 2005-09-01

A Split Happened on the Way to Reliable, Higher-Volume Gear Grinding

Bevel gear manufacturers live in one of two camps: the face hobbing/lapping camp, and the face milling/grinding camp.
FEATURE ARTICLES | 2005-01-01

Good Basic Design or Sophisticated Flank Optimizations - Each at the Right Time

More strength, less noise. Those are two major demands on gears, including bevel and hypoid gears.
TECHNICAL ARTICLES | 2003-05-01

The Two-Sided-Ground Bevel Cutting Tool

In the past, the blades of universal face hobbing cutters had to be resharpened on three faces. Those three faces formed the active part of the blade. In face hobbing, the effective cutting direction changes dramatically with respect to the shank of the blade. Depending on the individual ratio, it was found that optimal conditions for the chip removal action (side rake, side relief and hook angle) could just be established by adjusting all major parameters independently. This, in turn, results automatically in the need for the grinding or resharpening of the front face and the two relief surfaces in order to control side rake, hook angle and the relief and the relief angles of the cutting and clearance side.
TECHNICAL ARTICLES | 2001-09-01

What "Ease-Off" shows about Bevel and Hypoid Gears

The configuration of flank corrections on bevel gears is subject to relatively narrow restrictions. As far as the gear set is concerned, the requirement is for the greatest possible contact zone to minimize flank compression. However, sufficient reserves in tooth depth and longitudinal direction for tooth contact displacement should be present. From the machine - and particularly from the tool - point of view, there are restrictions as to the type and magnitude of crowning that can be realized. Crowning is a circular correction. Different kinds of crowning are distinguished by their direction. Length crowning, for example, is a circular (or 2nd order) material removal, starting at a reference point and extending in tooth length or face width.
TECHNICAL ARTICLES | 1996-01-01

The Next Step in Bevel Gear Metrology

In recent years, gear inspection requirements have changed considerably, but inspection methods have barely kept pace. The gap is especially noticeable in bevel gears, whose geometry has always made testing them a complicated, expensive and time-consuming process. Present roll test methods for determining flank form and quality of gear sets are hardly applicable to bevel gears at all, and the time, expense and sophistication required for coordinate measurement has limited its use to gear development, with only sampling occurring during production.
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