Is takt time the most misunderstood lean concept?
Is takt time the most misunderstood lean concept? My experiences suggests yes, although this surprises me quite a bit.
It’s not that the misunderstanding is highly significant, or has a dramatic impact on people’s actions. But when we ask the question of a group “what is takt time?”, to group that says they know what it means, I see them get it wrong 90+ percent of the time.
Here’s the answer we get: it’s the pace of your production process.
That’s your cycle time. And your cycle almost never equals your takt time. One of the reasons I believe people confuse it so often is because of the lingo. Do we need to use takt time? Half the people think TAKT is an acronym for something. Most wouldn’t know that it’s actually a German word for beat (as in drum beat), adopted by the Japanese and in term by the lean community. But why don’t we call it what it really is:
Customer Demand Rate
Is that hard to understand it’s meaning? Not really; seems pretty clear. This is an example where compliance to the lingo is superseding usefulness.
But the relationship between customer demand rate and cycle time matters, because it helps us understand the waste and opportunity. Here’s the formula used most often, and shared in Mike Rother and Rick Harris’ Creating Continuous Flow:
takt time = your available work time per shift / customer demand per shift
As much as I respect Mike and Rick, I don’t even think this formula is right. It’s mostly right, but saying “shift” assumes a lot about what you’re looking at. Even LEI’s own Lean Lexicon uses “per day” which is also too specific. To be fair, their book is focused on building manufacturing cells, and so shift might be a good choice. But the first question should be “over what time period are we evaluating our operation against the customer demand rate?”
In a previous Leading Lean column titled Save the Heart of the Idea, I describe the use of takt time to K-Mart. K-Mart isn’t thinking about a shift, they are thinking about a smaller block of time. Consider McDonald’s. They also aren’t worried about a shift. They are worried about smaller blocks of time. The operational processes must adjust sometime on an hourly basis driven by the planned and known changes in the customer demand rate. The takt time is different from 11:30 – 1 than it is from 2-4. This isn’t just variation in demand; it’s specific shifts in demand.
Unless your process is waste free, if your cycle time equals your takt time, you will miss customer orders. Congratulations if you’ve achieved this ideal. But the goal is not to get cycle time to match takt time; the goal is to make sure that a stable process including its waste is meeting customer demand. Then you work towards eliminating that waste. But that’s a useful way to think about takt time. Your cycle time plus your waste must be able to match up. And mathematically, the amount of waste grows as you go back into the process, and so therefore each preceding segment of the process must be running a little faster.
Takt time is a very useful concept. It helps you understand what you are building towards. It helps you align your process towards the needs. When we fail to grasp the purpose of the concept and boil it down to only a formula, or worse, a wrong definition, we lose all of the benefit.
It is issues like this that help demonstrate that lean is not just common sense as many like to claim. On the surface, yes, it just makes sense. But when you get into real application and understanding, there are many nuances which subtle changes in meaning can have a big impact. Lean isn’t easy. If it was, everyone would be successful at it, and it would no longer be a competitive advantage.
Reflection question: How have you used takt time to design, manage, and improve your process? How important is having a common interpretation to your organization?
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