Introduction to Gear Design 2nd Edition Charles D. Schultz, p.e. Beyta Gear Service Winfield, IL Sample — BD Tech Concepts LLC ii Introduction to Gear Design For information, contact: Beyta Gear Service Charles D. Schultz, p.e. 0N230 County Farm Road Wineld, IL 60190 [email protected] (630) 209-1652 Visit Beyta Gear Service on the web: http://BeytaGear.com ©1987, 2004 Charles D. Schultz All rights reserved. Self-publishedSample by Charles — D. Schultz, BDBeyta TechGear Service. Concepts LLC Document typesetting and diagram conversions by BD Tech Concepts LLC — 2015. Statement of Non-Liability Due to today’s legal climate, it is necessary to state that this book has been written for general education purposes only. Nothing written in these pages should be considered to be denitive advice about any specic situation. Dedication One of the things I have enjoyed most about being in the gear industry is the opportunity to learn from some really great people. It isn’t possible to list them all here but I’m sure they know who they are. It was their example that lead me to write this book. Whatever good comes from this eort I owe to them. Sample — BD Tech Concepts LLC iii Sample — BD Tech Concepts LLC Contents Dedication iii Introduction ix About the 2nd Edition....................................... ix 1 How to Use This Book1 2 What Kind of Gears Should I Use?3 Parallel-Shaft Gears........................................3 Intersecting-Shaft Gears......................................5 Non-Intersecting-Shaft Gears...................................6 3 What Should They Be Made Of?9 Rating Calculations........................................9 Gear Materials and Heat Treatment...............................9 The Gear-Design Process..................................... 16 4 What Should They Look Like? 17 Mounting Characteristics..................................... 17 Backlash.............................................. 17 Blank Tolerancing......................................... 17 Quality Classes........................................... 19 Surface Finish........................................... 19 Blank Design............................................ 19 Tooth-Form Selection....................................... 21 5 How Should They Be Made? 29 Milling............................................... 29 Hobbing............................................... 29 ShapingSample............................................... — BD Tech Concepts LLC 33 Broaching.............................................. 40 Lapping............................................... 40 Shaving............................................... 40 Honing............................................... 43 Gear Grinding........................................... 43 Form Grinders........................................ 43 Generating Grinders..................................... 43 Bevel Gears............................................. 46 Worm Gears............................................ 47 v vi Introduction to Gear Design 6 How Should They Be Inspected? 49 7 Where Do I Look For Help? 53 8 Acknowledgments 55 9 About the Author 57 Sample — BD Tech Concepts LLC List of Figures 2.1 Parallel-Shaft Gear Types..................................5 2.2 Intersecting-Shaft Gear Types...............................7 2.3 Non-Intersecting-Shaft Gear Types............................7 3.1 Critical Sections in Typical Parts.............................. 11 3.2 Mid-Band Jominy Hardness vs. Alloy........................... 13 3.3 Approximate Min. Core Hardness vs. Alloy........................ 13 3.4 Jominy Position vs. Critical Section............................ 14 3.5 AISI Numbering System for Steel............................. 14 4.1 Anti-Backlash Methods................................... 18 5.1 Hob Nomenclature — 1................................... 34 5.2 Hob Nomenclature — 2................................... 35 5.3 Hobbing-Clearance Diagram................................ 36 5.4 Double-Helical Gap-Width Diagram............................ 37 5.5 Shaper-Cutter Nomenclature................................ 38 5.6 Shaper-Cutter Clearance Diagram............................. 39 5.7 Shaving-Cutter Nomenclature............................... 42 5.8 Hob-Dipping Diagram................................... 44 5.9 Tooth Modications..................................... 44 5.10 Gear Grinder Types..................................... 45 5.11 Grinding-Wheel Interference on Cluster Gears...................... 46 5.12 Bevel-Cutter Interference with Front Shaft........................ 48 5.13 Worm-Gear Throat Diameter................................ 48 6.1 Bearing Pattern Checks................................... 50 Sample — BD Tech Concepts LLC vii List of Tables 2.1 Relative Characteristics of Gear Types...........................4 3.1 Popular Gear Materials................................... 10 3.2 Approximate Minimum Hardenability of 1045, 4140, 4150, & 4340........... 15 4.1 Typical Gear-Blank Tolerances............................... 20 4.2 Outside-Diameter Tolerances................................ 21 4.3 Gear-Blank Standards.................................... 22 4.4 Minimum-Suggested Quality Level vs. Pitch-Line Velocity............... 23 4.5 Achievable AGMA 2000 Quality Levels by Manufacturing Method........... 23 4.6 Achievable Tooth-Surface Finishes by Manufacturing Method............. 24 4.7 Surface-Finish Description................................. 25 4.8 Surface Finish vs. Tolerance................................ 26 4.9 Popular Tooth Forms.................................... 27 5.1 Normally-Available Milling Cutters............................ 30 5.2 Normally-Available Gear Hobs............................... 31 5.3 Normally-Available Spline Hobs.............................. 32 5.4 Minimum Number of Teeth to Avoid Undercutting.................... 39 5.5 Shaper-Cutter Teeth vs. Minimum Internal Gear Teeth to Avoid Interference..... 41 6.1 Sampling Plans....................................... 50 Sample — BD Tech Concepts LLC viii Introduction Albert Einstein once said: “Things should be made as simple as possible, but no simpler.” This book is an attempt to apply that principle to gear design by presenting information from a manufacturing point-of-view rather than a theoretical one. There are no great advances in gear technology described here. The topics discussed are all covered in greater detail in other books, some of which are listed in the “reference” section. The author hopes that this little volume will be of use to the occasional gear designer as a source of handy information and direction to more complete answers to the questions that arise during the design process. About the 2nd Edition After nishing this book in 1987 I vowed never to write another gear book. During the years since, however, I came to look at this little volume with a more critical eye and decided it needed just a little updating. What started out as a simple “scan it into the computer and make it look more modern” project grew into a major re-writing eort. I’ve tried to incorporate the lessons learned in 10 years of busy engineering practice at Milwaukee Gear and Pittsburgh Gear. I hope the additional gures and tables will be of value. Despite the modern convenience of spell check, I’m sure there are a few typos left, and that a 3rd edition will be needed in a few years to correct them.1 Sample — BD Tech Concepts LLC 1Editor’s note: This document is a 2015 revision based on a scan of the 2nd Edition. All content has been preserved, but has been converted to PDF text and vector diagrams, along with new editing, numbering, formatting, typesetting, and internal and external hyperlinks. ix Sample — BD Tech Concepts LLC Chapter 1 How to Use This Book Every gear engineer must answer a series of ques- Somewhere between questions 1 and 2 the tions before he can complete a design. The in- size of the gears must be determined through formation in this book is organized in the usual a rating-calculation procedure. This subject is sequence of these questions: not covered in this book for reasons that will be discussed later. A list of references has been pro- 1. What kind of gears should I use? vided to assist you in getting the answer to that 2. What should they be made of? question, and any others which this book raises for you. 3. What should they look like? 4. How should they be made? 5. How should they be inspected? Sample — BD Tech Concepts LLC 1 Sample — BD Tech Concepts LLC Chapter 2 What Kind of Gears Should I Use? Successful gear systems often depend as much type of gear has become the “standard” due to on selecting the right gear for the job as on the its unique characteristics. Table 2.1 shows the proper design of the individual parts. Gears can most common kinds of gears, organized by shaft be made in a wide variety of forms, each with its orientation, showing their relative characteristics own strengths and weaknesses. In some applica- compared to other types of the same shaft orien- tions dierent gear types can be used with equal tation. Additional comments on each are made success. There are other cases where a specic in the following paragraphs. Parallel-Sha Gears face of the gear. This “face” contact ratio is added to the “prole” contact ratio of the spur gear to Spur gears are by far the most common type of give a “total” contact ratio that can be tailored parallel-shaft gear. They are simple to design, to meet higher load requirements and operating highly ecient, and relatively