' RUDOLPH WlLLARQ NORTH CAROLINA STATE UNIVERSITY FURNITURE CONSTRUCTION by Rudolph Wi11 ard Furniture Manufacturing and Management Curriculum North Carolina State University Fourth Edition Under the Sponsorship of: The Foscue Furniture Fund The Southern Furniture Manufacturers Association and the School of Engineering North Carolina State University Price $12.00 Copyright 1970, 1975, 1982 De pa rtment of I ndu str ia1 En gineer ing North Carolina State University Raleigh, North Carolina All rights reserved. This book, or any part thereof, may not be reproduced in any form without written permission of the Head of the Department of Industrial Engineering, North Carolina State University. Printed in United States of America FOREWORD The School of Engineering at North Carolina State University offers a four-year curricul um in Furniture Manufacturing and Management within the Industrial Engineering Department. The purpose of this program is to provide young men and women with academic prepartation for a career in the furniture industry. The preparation and publication of this text has been made possible through support from the Foscue Furniture Fund. We acknowledge the help and encouragement from the Furniture Founda- tion, Inc., and its president, Dr. Henry A. Foscue, who has been responsible for the growth and many improvements in the Furniture Manufacturing and Management Curriculum. L. K. Monteith Dean of Engineering North Carol ina State University i FURNITURE CONSTRUCTION Preface to the Fourth Edition The fourth edition of Furniture Construction is the first one pub- 1 ished since Rudolph Willard's death in 1981. This book and its com- panion volume, Production Woodworking Equipment, are testimony to Rudy's great contribution to the development of the Furniture Manu- facturing and Management Curriculum. We will always cherish his memory. Edward L. Clark and I have revised many details of the text to reflect current practice in manufacturing, but we trust that the book retains the unique fl avor Rudy gave it original ly. All comments, suggestions, and criticisms of the book are appre- ciated. Anco L. Prak James T. Ryan Professor of Industrial Engineering in charge of Furniture Manufacturing and Management North Carolina State University Raleigh, NC July 1982 TABLE OF CONTENTS Page Chapter 1 PRODUCT ENGINEERING................. 1 Chapter 2 MECHANICS OF FURNITURE CONSTRUCTION ......... 9 Chapter 3 CHARACTERISTICS OF WOOD AND LUMBER ......... 29 Chapter 4 CHARACTERISTICS OF VENEER AND PLYWOOD ........ 41 Chapter 5 PLASTICS IN FURNITURE CONSTRUCTION ......... 63 Chapter 6 INTERNAL STRESSES .................. 79 Chapter 7 WOOD JOINTS..................... 89 Chapter 8 MECHANICAL FASTENERS ................ 111 Chapter 9 MINIMIZING COSTS .................. 129 Chapter 10 PERMANENT SPECIFICATIONS .............. 147 Chapter 11 CASEGOODS ...................... 179 Chapter 12 CASEGOODS .RIGIDITY ................ 199 Chapter 13 DRAWERS ....................... 215 Chapter 14 CUPBOARDS AND DOORS ................. 231 Chapter 15 CHAIRS ....................... 253 Chapter 16 UPHOLSTERY FRAMES .................. 287 Chapter 17 BEDS AND TABLES ................... 293 Chapter 18 PACKAGING...................... 307 CHAPTER 1 PRODUCT ENGINEERING In examining the broad field of product engineering, one must look at the steps normally followed in introducing a new suite or new item into a line of furniture. Each step essentially involves only one functional area of the organization. An outline of this procedure is given below: Steps Functional Area 1. Recognize a need Sales 2. Determine general type and price range Sales 3. Design for appearance Design 4.................................................................... Approve design for marketability Sales 5. Work out details of construction Product Engineering 6. Prepare preliminary cost estimate Cost Accounting 7. Compare cost estimate with desired price range and modify design if necessary Sales 8. Rework construction details for modifications in design Product Engineering 9. Build samples according to the detailed construction drawing Shop 10. Check samples for marketability and modify if necessary Sales --------------------_______c____________---------------------------- 11. Determine price, show samples at market, and take orders Sales 12. Prepare final drawings, bills of materials, and machining sequences Product Engineering 13. Make route tickets, jigs, and fixtures Product Engineering 14. Issue manufacturing order for first lot Production Management The first four steps answer the question, "What will sell?" The next six steps are a feasibility study to determine how to make a saleable item at a profit. The final steps involve the mechanics of getting the furniture sold and into production. For the purpose of clarity, the above procedure shows a sharp separation of the three main functions of sales, design, and product engineering. Under actual circumstances, there is a great deal of overlapping and cooperation required to introduce new items to the buying public efficiently . The sales management and design force combine a knowledge of the market place and artistic talent to develop pieces of furniture that people will want and be willing to pay for. Product engineering is g ven the difficirlt job of working out the details of exactly how the piece should be constructed in order to achieve: a, Satisfactory performance in the final user s home 1 b. Economical manufacture with machinery, equipment, methods, and personnel available in the plant. The ultimate objective is a piece of furniture with satisfactory appearance, comfort, durability, functional utility, quality, and satisfaction that can be sold at a maximum profit. This book does not deal with artistic appearance design or the merchandising function except as incidentals. It does deal with the product engineering functions, and good product engineering should involve the following: 1. Knowledge of problems and difficulties encountered by the retail dealer and by the ultimate customer with furniture in use in the home and the relative frequency and impor- tance of the different types of problems. 2. Knowledge of stresses, changes in temperature and humidity, and other conditions which the product will be subjected to in getting it from the factory to the consumer's home and in normal use in the home. 3. Knowledge of the principles of physics and strength of materials which permit analysis of forces imposed on the furniture in use and its ability to resist those forces. 4. Characteristics of available materials which affect construction, processing, and final trouble-free perfor- mance. 5. Ways and means to eliminate or at least minimize customer p rob1ems. 6. Knowledge of equipment, processes, and personnel in the plant which is to produce the furniture. 7. Creative imagination as to alternatives in construction and processing. If two or more alternatives will achieve the objective of trouble-free performance, they should be com- pared on the basis of cost and the most economical alter- native selected. 8. Awareness of new materials, inventions, machines, etc. These points will be discussed in more detail later. Product engineering does not deal primarily with appearance, a5 this is in the area of design. However, minor changes in appearance sometimes make major changes in cost. In such cases, the product engineer should suggest changes to design and sales. For example, most flush joints cost more than joints which are nearly flush. In many instances, the general appearance of a nearly flush joint is as acceptable as a truly flush joint. 2 Comfort is an important feature in chairs, sofas, and other sitting furni- ture; it should also be considered in tables and desks at which people sit. It is important in bedding items such as springs, mattresses, and pillows but these are outside the scope of this book. Responsibility for comfort is divided between the designer and the product engineer. Although the finish on a piece of furniture is of prime importance in cus- tomer satisfaction, it has little connection with construction. In the choice among construction alternatives, it is rare that the choice of al- ternatives will affect the finish. On exposed surfaces of furniture, choice of species of wood is generally governed by considerations of sales and mar- keting rather than product engineering. An exception might be the choice of a hard species like maple instead of a soft species like basswood. The two species are much alike in appearance, but maple resists bruises and dents much better than basswood. But in most cases, choice of species for exposed parts is determined by the appearance desired. The importance of good product engineering should not be affected by the quality and price range of the furniture. It should be equally important in low, medium, and high price ranges. Since one of the main objectives of product engineering is to plan a product which will give satisfaction to the customer, it is important to guard against customer problems and dissatisfaction. However, it is difficult to guard against problems in general ; effective prevention implies knowledge of specifically what problems to guard against. This sounds sensible and simple, but in practice, it is not so easy. Problems can be placed into the following categories: a. Those which your customers have had and reported to you. b. Those which your customers may have had but did not report to you. c. Those which customers of other factories have had and