Ken Susnjara, President of Thermwood Corporation, with his book Furniture Manufacturing in the New Millennium, has provided a valuable service to furniture manufacturers seeking to survive in today's competitive world. This book is of value to manufacturers considering a purchase of a CNC machine as well as for those manufacturers currently using these machines in their production. A book authored by the president of a major CNC manufacturer is immediately suspect. One expects it to be heavily slanted to the author's machines, simply a sales brochure in book format, point out the features of the manufacturer's machines and deficiencies in all others. Susnjara has generally succeeded in navigating the fine line between advocating one machine and the technology common to the industry.
Without a doubt, not all readers will agree with Susnjara's methods of calculating costs of parts, by which he essentially demonstrates that setup time for a machine results in the major cost component. This conclusion is significantly different that the generally accepted viewpoint that the faster the machine cuts parts, the better the result on the bottom line. The equation presented in the first four chapters challenge this belief and offers sufficient evidence that the furniture industry should at least look at their costs in a different manner by plugging their specific numbers into these equations. It is suspected that if this were done, there are many manufacturers who will need to rethink the basis for many of their equipment purchases.
Furniture production is undergoing a fundamental change with the lower number of parts per cutting. Susnjara shows that with a batch system of producing parts, using a series of one-function machines that require handling of parts and setup time changing from one part to another part, cost per part increases significantly when the number of parts produced is reduced from 1,000 to 100 per batch. It is shown that using a machine having a faster feed speed to cut the parts does little to reduce the cost per part. However, significant reductions in the cost per part are possible, even with small numbers of parts per run, if the setup time for the machine can be reduced. From Susnjara's perspective, this is the advantage realized by CNC routers, not the faster run times. Reducing the time to set up the machine when changing from one part to another significantly reduces the cost per part. This reduces the manufacturing costs for the producer and provides the opportunity for significantly affecting the bottom line.
A furniture fabrication cell is discussed in one of the chapters. This is a revolutionary concept for the use of CNC routers in which all parts of an article of furniture are produced on one machine as opposed to making interchangeable parts, each with a different machine. Susnjara believes it is now time for the furniture industry to move from making interchangeable parts on a variety of task specific machines and assembling the parts into the finished piece on a production line to making furniture in dedicated fabrication cells. These fabrication cells would perform all machining processes on a part on a single machine and changes from one part to another part on the same machine could occur with essentially no setup time. An easy to use software program is provided to allow readers to evaluate this concept in their own situation.
Manufacturing cells have been a research and discussion topic throughout the furniture industry for a number of years but to date have not been widely accepted. The furniture industry has been notorious for the absence of an innovative spirit - "if my competitor is doing the same thing I am doing, there is no reason to change what I am doing." As Susnjara points out in numerous places in his book, this is not the way the industry will survive and thrive in the new competitive arena. If fabrication cells, or manufacturing cells, or whatever the term ultimately adopted, is instituted by a company, and Susnjara's thesis is correct, that company will enjoy a significant competitive advantage which will either force others out of business or force them to adopt similar practices. Whether the furniture industry that the proposed changes in manufacturing concepts is warranted remains to be seen.
Finally, Susnjara includes a chapter entitled "CNC Router Design" that provides an excellent overview of the various technologies included in router design and is required reading for anyone contemplating purchase of a CNC router. This portion of the book could have obviously become a sales pitch for Thermwood routers. With one or two exceptions, Susnjara has avoided this trap in discussing various engineering choices available in commercial routers. Susnjara discusses a variety of engineering methods to accomplish the same end result and the positives and negatives of these choices. As Susnjara points out, the only truly correct way to judge the various technologies used by the CNC manufacturers is to observe the results. This chapter is a must read for the individuals contemplating purchase of a CNC router.
This chapter also provides the pros and cons for a number of different design methods to accomplish the same task. The author state that there are many technical factors that can be addressed in more than one way and he provides the advantages and the disadvantages of the various ways. For example, massive machines are accurate but usually have a limitation in the rate of acceleration and deceleration due to the mass. What is needed is a rigid, lightweight machine that does not sacrifice accuracy in obtaining high rates of acceleration and deceleration. Another section of this chapter is devoted to various types of drive mechanisms employed to move the machine. The pros and cons of each method are discussed, Also covered is the whip in the lead screw and various methods employed by the machine manufacturers to compensate for this whip. Other topics covered are spindle design and spindle bearings, lubrication techniques, part hold down methods, and CNC controllers.
This book will undoubtedly find many critics within the furniture industry. It is not a traditional textbook but it is not blatant sales literature for the author's company. Whether the reader agrees that the proposed changes in furniture manufacturing techniques to encompass a fabrication cell is warranted, the book introduces innovative and revolutionary ideas, which should be obvious to all readers.
M. W. Kelly NC State University May 1998
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