In this chapter Taiichi Ohno illustrates the idea that “misconceptions reduce productivity” by telling several stories from the Gemba at Toyota. The point Ohno makes in this chapter is that demonstrating the superiority of one piece flow is a simple thing, yet it something rarely seen on the Gemba.
In the first story Ohno wanted to show that inspecting one at a time was quicker and took less work than inspecting in batch. “Try it one at a time” Ohno says. “No, this way is faster” replies the inspector. After trying one at a time, the inspector completed 5,000 pieces in regular hours, rather than requiring overtime as the batch method did.
People have the misconception that picking up 20 or 30 pieces and lining them up on the table and inspecting them all at once is faster. Once you try it, and you see it’s easier, quicker, and less tiring to do one at a time people lose their misconception. Ohno recognizes here that there may be an objection from the worker due to the lost overtime pay.
Ohno tells another story from Toyota of a process to machine a hole in bar stock, shortly after the WWII (likely the late 1940s or early 1950s). The machine operator was hand feeding the machine even though the machine had automatic feed machine. The young machine operator proudly tells Ohno that he is making 80 pieces per day.
When asked why the operator didn’t just start the machine and let it run on automatic feed, the operator replied “I think it’s faster to operate it manually.” The reasons given were that since automatic feed was faster the tool wore down quicker, resulting in defective products. Manual feed let the operator have a better feel for the wear on the tool.
“How long does it take to make a hole?” Ohno asked. “Thirty seconds.” The young operator replied. “That’s 120 pieces per hour.” Ohno pointed out. The young operator was silent. There were 7 working hours per shift in those days. The operator was only producing 80 pieces, when at 30 seconds per piece he could have done that in 40 minutes.
Ohno points out “You should put in more than one hour’s work per day.” The young operator protests that he is working hard. Ohno’s point is that the worker things he is working productively (working hard) when he is not at all productive (high value added output).
The manual process takes 30 seconds. The operator is working hard. The automatic process takes 40 seconds. The operator has the misconception that it is faster. But it is less productive at the end of the day. This is because after making 3 pieces by hand the tool is hot and begins to dull. So the operator takes the tool to the grinder to sharpen it. Then he makes 3 more parts at 30 seconds per piece. The cycle repeats. The operator thinks this is productive work.
Ohno demonstrates how you can produce 80 pieces more productively. You need one part every 5 minutes to produce 80 in 7 hours. By using the automatic feed and making one piece every 40 seconds, you can let the machine run, let the tool get hot, cool naturally for 4 minutes, and run the next piece with no grinding needed. You can use the same tool for 30 or even 50 pieces without regrinding.
The grinding wheel is a shared resource. Not every operator has one. So when the young operator goes to regrind the tool there are 5 or 6 people standing there and waiting. A different lathe operator runs parts as fast as he can, then goes to regrind his tool also. So this results in a wait, and in the end you average only 2 parts every 10 minutes, even though you think you can make one piece every 30 seconds.
In the same way Ohno explains that some operators will place 10 or 15 parts on a drill press, drill them, and take the parts off and put them in a box. Then the next parts are loaded, drilled, unloaded. There is a lot of wasted motion and even though these workers think they are doing skilled, productive work, in the end they are less productive.
These stories are great demonstrations of the wastes (waiting, motion, transportation) associated with working in a batch and queue method. The chapter also demonstrates how people have the misconception that batching is faster.
This misconception is alive and well today. With the spread of Lean manufacturing and knowledge of the Toyota Production System, more people are implementing one piece flow. Yet there is still too much focus on local optimization (making things as fast as you can through one process) instead of overall optimization (making things as fast as you can through the whole process).
Look for examples of misconceptions that reduce productivity at your own company and use them to educate people about Lean transaction and Lean manufacturing, as Taiichi Ohno does in this chapter.