Engineering Expert Witness Blog

     Last week we wrapped up our discussion of vibration analysis.  It’s been a long time coming, but this week we’ll conclude our series on the many aspects of mechanical engineering by discussing machine design.  If you’ve been with us since the beginning of the series and you’re not a mechanical engineer, I’d venture to say you’re now impressed with the wide scope of issues with which mechanical engineering is concerned.

     In our preceding discussions we examined some basic concepts behind statics, dynamics, kinematics, strengths of materials, material science, thermodynamics, heat transfer, fluid mechanics, and vibrations.  This is the foundation of mechanical engineering know-how.  But when we consider machine design as a whole, we often have to keep in mind the old cliché, “Why reinvent the wheel?”  I say this because engineers have been designing machines and mechanical systems for hundreds of years.  Over this time, their design accomplishments have been collected, standardized, and tabulated in engineering handbooks and product catalogs to make things easier for future generations and to eliminate redundancy of work effort.  Put another way, why design nuts, bolts, pumps, heat exchangers, motors, gears, pulleys, and drive belts for a new machine when someone already designed them for similar applications in the past and they are readily available for quick purchase from suppliers?

     For example, suppose you had to design a machine that will be driven by an electric motor using sprockets and a roller chain.  This is the same method that your bicycle employs to transfer foot power applied to the pedals back to the rear wheel, which gets you rolling.  So, how do you come up with a chain that will do the job without breaking?

     To incorporate a sprocket and roller chain drive system into your machine design, you must first determine how much horsepower you will need to run the machine, the speed at which it must operate, and the conditions under which it will operate.  You can use this information to design a chain from scratch, then test it to see if it works, then have it custom manufactured.  Translation:  Lots of time, effort and money expended.  Or, you could get a hold of a book that’s been around since 1914, Machinery’s Handbook.  This is considered by many to be one of the best mechanical engineering reference handbooks of all time.  It contains tables of information that can be used to select standard, commercially available roller chains based on both horsepower and speed requirements.  It also has lots of other engineering-specific information on various other machine components.

     Based on our example above, I think you can conclude that the fastest, most economical route to take to construction of our mechanism is to use as many standardized, commercially available components as possible.  Knowing where to find information on these components and how to use them is very important to the success of your design, and this is precisely the information that you would have picked up during your final year of study towards earning a Bachelor’s Degree in Mechanical Engineering.    As a student, you would have been required to take at least a few machine design courses.

     Well, that’s it for our series on understanding the basics of mechanical engineering.  I hope you enjoyed it and it helped you to better understand the fundamentals of what mechanical engineering is all about.

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