Why some cars are lemons, and what to do about it
Why does a high-tech production line pump out the occasional lemon?
Unfortunately, no matter how good a manufacturer is at making things, the processes they use always produce slight variations from one item to the next. Take something simple like a biro pen, which consists of four main parts. If we take apart the two critical components, the barrel and the refill and measure the area where they fit together, you’d notice that the refill is slightly larger than where it fits into the barrel, which means they require a little bit of force to fit together.
This slight interference is crucial to make sure the two parts stay together. If the refill is too small or the barrel too big then the refill will fall out. On the other hand, if the barrel is too small and the refill too big then you won’t be able to push them together in the first place. In other words, there is a sweet spot of barrel and refill size ranges with which a viable pen can be made. Anything outside this and the resulting pen will not meet the customer’s expectation of a pen, making a lemon if you will. This sweet range is called the ‘specification’.
If you measure a thousand pens, you’ll find a lot of variation. Virtually none of the parts will be the same size but they’ll be close. The range of variations is called the ‘tolerance’.
So, if the range of tolerance is inside the range of specification you’ll be making good pens. If it’s outside the range of specification, you’ll begin to make lemon pens and the further it is outside the more lemons you’ll make.
Are certain products more susceptible to being lemons?
When products have hundreds of parts, just one of them being out of specification could make the whole thing fail. The task of analysing the tolerances of all the components and how much they could possibly vary is incredibly complex on something like a car and costs a great deal of money and time to get right. The willingness and ability to do this is the main reason why some manufacturers seem to have more faults than others.
Are lemons the fault of machines or man?
To further complicate things, many items are assembled by hand which adds a human element to the mix. You know how it goes, give 10 people a task and they’ll do it 10 different ways.
While diversity is a good in most things, it’s bad when it comes to screwing things together and having them work consistently. Depending on what the product is, something put together incorrectly can be life threatening. Ultimately, this too is a design issue, since a good part or process design will be one that eliminates choice in how it’s assembled.