When it comes to the economics of assembly machines, faster is always better. Every minute that it runs, a fast machine produces more goods—and more profits—than an otherwise similar slow machine. So why don’t you simply crank up the speed on your existing assembly lines or design faster, new machines?

The answer is that speed, for all its economic advantages, has some steep costs from an engineering perspective. Faster assembly lines typically suffer from resonance and vibration problems. These fast machines tend to operate close to the critical speed of gears and other moving components, and they may have more violent reciprocating movements as well. As a result, they experience more wear and need more aggressive maintenance and lubrication schedules.