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Robert Errichello

Robert Errichello heads his own gear consulting firm, GEARTECH, and is founder of GEARTECH Software, Inc. He has over 50 years of industrial experience. He has been a consultant to the gear industry for the past 37 years and to over 50 wind turbine manufacturers, purchasers, operators, and researchers. He has taught courses in material science, fracture mechanics, vibration, and machine design at San Francisco State University and the University of California at Berkeley. He has presented numerous seminars on design, analysis, lubrication, and failure analysis of gears and bearings to professional societies, technical schools, and the gear, bearing, and lubrication industries. A graduate of the University of California at Berkeley, Errichello holds BS and MS degrees in mechanical engineering and a Master of Engineering degree in structural dynamics. He is a member of several AGMA Committees, including the AGMA Gear Rating Committee, AGMA/AWEA Wind Turbine Committee, ASM International, ASME Power Transmission and Gearing Committee, STLE, NREL GRC, and the Montana Society of Engineers. Bob has published over 80 articles on design, analysis, and application of gears, and is the author of three widely used computer programs for design and analysis of gears. He is technical editor for GEAR TECHNOLOGY and STLE Tribology Transactions. Errichello is recipient of the AGMA TDEC Award, the AGMA E.P. Connell Award, the AGMA Lifetime Achievement Award, the STLE Wilbur Deutch Memorial Award, the 2015 STLE Edmond E. Bisson Award, and the AWEA Technical Achievement Award.

Articles by Robert Errichello

TECHNICAL ARTICLES | 2024-02-16

Morphology of Wear on Tapered-Roller Bearing Roller Ends and Thrust Ribs

This report investigates the wear morphology on the large end of tapered rollers and the inner ring's large end rib on a planet carrier TRB from a multi-megawatt wind turbine gearbox. The literature on abrasive wear has many classifications, including 2-body abrasion, 3-body abrasion, scratches, grooving abrasion, rolling abrasion, cutting abrasion, and plowing abrasion. For this analysis, we have selected grooving abrasion, a common problem in wind turbine gearboxes and a prominent failure mode on many bearings, particularly planetary carrier bearings and planet bearings. Grooving abrasion is frequently observed on cylindrical roller bearings (CRB) and tapered roller bearings (TRB). Fitzsimmons and Clevenger conducted tests on roller end/rib wear for TRBs with contaminated gear oil, and they provided an excellent explanation of the mechanism.

TECHNICAL ARTICLES | 2023-08-28

Influence of Grain Size on Metallurgical Properties

This report discusses grain size and its influence on metallurgical properties including its effect on yield strength, ultimate strength, fatigue strength, and fracture toughness. Also discussed are manufacturing issues such as heat treatment, hardenability, and machinability. 

TECHNICAL ARTICLES | 2023-07-27

Profile Shift

The objective of this report is to determine the origin of the phrase “profile shift.” Several technical books, technical papers, and industrial standards were reviewed for nomenclature associated with profile shift. The phrase “profile shift” translates directly to the German term “Profilverschiebung,” which originated in the last quarter of the 19th century. At first, profile shift was used to avoid undercutting pinions with small numbers of teeth. Later, it was recognized that profile shift improved the load capacity of the gear mesh and extended the service life of manufacturing tools.

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 | 2022-08-30

Nomenclature of Micropitting

An overview of the incubation, nucleation and growth, and morphology of this common failure mode, along with the appropriate terminology to describe it.

TECHNICAL ARTICLES | 2022-05-19

Defining the Tooth Flank Temperature in High-Speed Gears

The objective of this paper is to improve the methodology for determining the tooth flank temperature. Two methods are proposed for assessing scuffing risk when applying AGMA 925 for high-speed gears. Both methods provide similar results.

TECHNICAL ARTICLES | 2021-11-01

The “Metallurgical Notch” in Type B Induction Hardened Gears

Advantages of induction hardening over carburizing, as prepared for the AGMA Metallurgy Committee.
TECHNICAL ARTICLES | 2020-09-01

History of the AGMA J-FACTOR

I felt a tap on my shoulder. Turning, I saw the chief draftsman who said, "You're in charge of gears." And he walked away. Dumbfounded, I stared at the back of his head, and sat down at my drafting board. It was November, 1963, shortly after JFK was assassinated, and after I was discharged from the U.S. Army.
FEATURE ARTICLES | 2020-06-01

Ten Top Books for Gear Failure Analysis

The purpose of this article is to provide an overview of proven books or standards dealing with failure analysis. Following you will find a short description of ten books or standards. At the end of the document you will find an overview and a detailed reference list.
ASK THE EXPERT | 2018-09-01

Lubrication: Viscosity and Macropitting

A reader asks: Is the ISO VG 320 adequate, or should a higher viscosity grade be used? How can we stop macropitting in gear teeth?
VOICES | 2016-03-01

Critique of the ISO 15144-1 Method to Predict the Risk of Micropitting

There exists an ongoing, urgent need for a rating method to assess micropitting risk, as AGMA considers it a "a very significant failure mode for rolling element bearings and gear teeth - especially in gearbox applications such as wind turbines."
TECHNICAL ARTICLES | 2015-07-01

Elastohydrodynamic Lubrication (EHL): A Review

This review of elastohydrodynamic lubrication (EHL) was derived from many excellent sources (Refs. 1–5). The review of Blok’s flash temperature theory was derived from his publications (Refs. 6–9). An excellent general reference on all aspects of tribology is the Encyclopedia of Tribology (Ref. 10).
ASK THE EXPERT | 2015-03-01

Measuring Residual Stress in Gears

I have heard that X-ray diffraction does not tell the whole story and that I should really run a fatigue test. I understand this may be the best way, but is there another method that gives a high degree of confidence in the residual stress measurement?
ASK THE EXPERT | 2014-09-01

Lubrication Lexicon

I must confess I sometimes find myself a bit dazed when discussing lubrication issues with either staff or vendors. The terminology seems to be all over the lot, with some terms having double meanings. Can you help cut through the confusion?
ASK THE EXPERT | 2014-08-01

The Pros and Cons of Fully Ground Root Fillets

For maximum life in carburized and ground gearing, I have been advised that fully grinding a radius into the root gives maximum resistance against fatigue failures. Others have advised that a hobbed and unground radius root form is best. Which is best, and why?
ASK THE EXPERT | 2013-09-01

Lubrication Specification and Methodology

A reader asks about how to specify a method of lubrication for a speed reducer with a three-stage helical gear with a low peripheral speed.
TECHNICAL ARTICLES | 2012-11-01

Morphology of Micropitting

Understanding the morphology of micropitting is critical in determining the root cause of failure. Examples of micropitting in gears and rolling-element bearings are presented to illustrate morphological variations that can occur in practice.
TECHNICAL ARTICLES | 2005-11-01

The Fatigue Endurance Limit: A Myth

Review of "Gigacycle Fatigue in Mechanical Practice," by Claude Bathias and Paul C. Paris
FEATURE ARTICLES | 2003-09-01

The Ten Commandments of Gear Failure Analysis

I. Inspect failed components as soon as possible. If an early on-site inspection is not possible, someone at the site must preserve the evidence based on your instructions.
INDUSTRY NEWS | 2001-05-01

Calculating Dynamic Loads, Sizing Worm Gears and Figuring Geometry Factors

Q&A is an interactive gear forum. Send us you gear design, manufacturing, inspection or other related questions, and we will pass them to our panel of experts.
FEATURE ARTICLES | 2000-05-01

Geoffrey Parrish, Carburizing: Microstructures and Properties, 2nd ed., ASM, 1999, 247 pages.

Geoffrey Parrish has updated and expanded his previous book: The Influence of Microstructure on the Properties of Case-Carburized Components. It now contains at least twice the material. References and bibliography include 449 citations.
FEATURE ARTICLES | 1994-03-01

Photography of Gear Failures

Photography is an essential part of gear failure analysis. It not only provides a fast, convenient way to accurately document the appearance of gear failure, but also is an effective diagnostic tool because the magnification obtained through photographic enlargement and slide projection often discloses evidence that may have been missed if the gears were not photographed.
VOICES | 1992-09-01

Reader Dialogue: Functional Measurement of Gears; More Good Gear Books

From time to time, the editors of "Shop Floor" receive correspondence from readers relating to particular articles they have written for past issues. As one of the purposes of this column is to provide a forum for the exchange of ideas, we reproduce here two of these letters and their replies. The subject of the first is the functional measurement of gears. (See Gear Technology, Sept/Oct, 1991, p. 17) Robert E. Smith writes the reply.
VOICES | 1992-05-01

The Top Ten Books for Gear Engineers

When I was new to gear engineering, I found the array of gear literature scare, and the information scattered and conflicting. After investigating the materials available, I set the goal of creating an annotated listing of the references. There are many valuable resources, but for this article I have selected ten of the best. These references, in my opinion, are the most useful, and cover the scope while minimizing redundancy.
TECHNICAL ARTICLES | 1991-11-01

A Rational Procedure for Designing Minimum-Weight Gears

A simple, closed-form procedure is presented for designing minimum-weight spur and helical gearsets. The procedure includes methods for optimizing addendum modification for maximum pitting and wear resistance, bending strength, or scuffing resistance.
INDUSTRY NEWS | 1991-09-01

Single Flank Measuring; Estimating Horsepower Capacity

Question: What is functional measurement and what is the best method for getting truthful answers?
TECHNICAL ARTICLES | 1991-07-01

The Lubrication of Gears - Part III

This is the final part of a three-part series on the basics of gear lubrication. It covers selection of lubricant types and viscosities, the application of lubricants, and a case history
TECHNICAL ARTICLES | 1991-05-01

The Lubrication of Gears - Part II

What follows is Part 2 of a three-part article covering the principles of gear lubrication. Part 2 gives an equation for calculating the lubricant film thickness, which determines whether the gears operate in the boundary, elastohydrodynamic, or full-film lubrication regime. An equation for Blok's flash temperature, which is used for predicting the risk of scuffing, is also given.
TECHNICAL ARTICLES | 1991-03-01

The Lubrication of Gears - Part 1

This is a three-part article explaining the principles of gear lubrication. It reviews current knowledge of the field of gear tribology and is intended for both gear designers and gear operators. Part 1 classifies gear tooth failures into five modes and explains the factors that a gear designer and operator must consider to avoid gear failures. It defines the nomenclature and gives a list of references for those interested in further research. It also contains an in-depth discussion of the gear tooth failure modes that are influenced by lubrication and gives methods for preventing gear tooth failures.
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