Critical Chain - Eliyahu M. Goldratt [59]
"But you solved it," he says, surprised.
Jim speaks for all of us, "If we did, we haven't noticed."
"You already said it all. The starting point is the bottleneck. To exploit it we must protect it against disruptions everywhere else in the process. That's why we must make sure that a pile of inventory will be built in front of it. But not a mountain, that will cause inventory, or lead time, to go too high. So . . ."
He stops talking, waiting for us to continue.
We look at each other. "So, we don't know how to do it," I say.
"Tie the first soldier with a rope to the slowest soldier, to the bottleneck. That's all. What's the point in tying all the soldiers to each other? It will only force inventory between them rather than allowing the inventory to flow toward the bottleneck and accumulate there. Of course, the length of the rope, we call it the buffer, will dictate how much inventory in total you allow."
I'm trying to digest.
Jim does the same, but aloud. "If we tie the first soldier to the bottleneck, then the first row will be forced to walk at the rate of the bottleneck. That's good, spreading of the troop is prevented. All the other soldiers, being faster than the bottleneck, will jam pack, some behind the first row, the others behind the bottleneck. So the troop will spread over a distance that will be almost equal to the length of the rope we choose. That's neat. It will also guarantee that there is a gap before the bottleneck, so if one of the upstream soldiers stops, the bottleneck can still proceed. The inventory, the safety, accumulates there. Very nice, Johnny."
"In practice," Johnny continues, "what we do is the following. First you identify the bottleneck. Then you choose the length of the buffer. Usually a good rule of thumb is to take the current production lead time and cut it in half. Then, you . . ."
So even in production they measure the buffer, the protection, in terms of time. What Johnny is talking about now is not too important for me. In projects, not like in production, the work is done only once. I will not be able to copy the mechanism from production, but I can transfer the concepts and find the appropriate mechanism. I have the key, I just have to follow the five steps.
I can already see the main questions I'll have to figure out the answers for. What is the bottleneck in projects? We have to tie the rope to something. How does one choose the buffer?
But I already see so many answers. Tying the rope will give the answer to the early start versus late start dilemma. It will also restrict the amount of work that is released, and therefore the problem of multi-tasking will be considerably reduced. I'll have to think much more about it, but I feel that the answers are around the corner.
Charlene stands up. "I'm sorry, but I have a class to teach. Johnny, there is something else I want to ask you. Local efficiencies and variances are wrong measurements. I fully accept. But what are the alternatives? What should we measure? Or do you suggest not using any operational measurements?"
"Not at all," he is quick to deny. "Do you want to schedule another meeting to discuss it?"
We all take out our diaries.
Chapter 16
"So far, does it make sense?" I ask them.
I can see how Mark, Ruth and even Fred are ready to jump down the throat of anybody who does not agree. Luckily, there are no targets.
The extent to which these three have become zealots is surprising. Their turnaround happened last session, when I guided the class to develop the solution. Not that they were dragging their feet before, but now it's like they have seen the light; they behave as if all their future depends on implementing it.
Tuesday morning all three came to my office and stepped all over each other trying to convince me to come to Genemodem and talk to Mark's team.
"The solution is almost against human nature," Mark was quite desperate. "I don't know how to persuade people to strip away their