Why Flow Counter Clockwise?
by Ron Pereira on September 30th, 2007.
When designing a u-shaped cell it is often recommened that material flow in a counter clockwise direction. Why is this?
It’s about the right hand
Research shows that most people are right handed. I have heard that as many as 85% to 90% are right handed. Why does this matter you might wonder?
Well, when you think about what happens in a cell we know that first we must pick the product up. Since we have to “aim” so to speak to pick it up we tend to want to use our dominate hand.
Further, once we have “added value” to the product we are ready to simply pass it on to the downstream process. There is not much “aiming” involved with simply placing something down.
So, with this known we can see why having things flow counter clockwise or “left hand inside” makes sense when most people are right handed. We pick up with our right hand (when we need to aim) then put it down with our left (when no aim is needed).
It’s about the horses
While the right hand dominate aspect may be the most common reason for flowing counter clockwise there is another reason that is quite amazing. Have you ever seen a horse race held where the horses ran clockwise? Probably not. In every horse race I have seen the horses run counter clockwise.
The same thing applies for track athletes and race cars. They also move around the track in a counter clockwise manner. You may not have ever given this much thought but there is actually quite a bit of “brain science” behind this. I must give credit to my friend Jon Miller for first explaining this to me. Well, he explained it to a lot of people in this post some time ago. He wrote:
One of the strongest reasons given for the innate “left hand inside” preference for human motion comes from brain science. According to a Professor Matsumoto, since the right brain processes spatial recognition human perception of space is stronger through the left side of vision (the hemispheres of the brain control opposite sides of the body).
When you are running “left hand inside” or counterclockwise, you have better visibility of space on the left side and you are able to run more comfortably, confidently, and quickly.
Here is a little test for you. If you don’t believe this brain science stuff head to the closest track and run a lap headed clockwise and time yourself. Then, take a rest and run another lap counterclockwise and time yourself. Chances are very good that your counter clockwise time will be several seconds faster than your clockwise time.
Of course you should do this a few times to make sure. In addition to learning about lean you will be doing some great exercising… which is lean as well I guess. Yeah, I know, that was a really bad joke.
My cell flows clockwise… am I evil?
So, what to do if your cell or cells flow clockwise? Does this mean you are not lean? Of course not. In fact, I recently talked to some folks who initially designed a cell to flow counter clockwise but after piloting it the operators complained and offered some reasons why they preferred to flow clockwise which the engineers took into consideration and made the changes.
So, take this article with a grain of salt and be sure to test whatever solution you implement. In the end, the folks working on the line need to be comfortable with whatever you come up with.
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So I assume if you do happen to have a bunch of lefties clockwise movement may be best, right?
Thanks for this post. It was great. I am now a subsciber to your blog. Keep up the great work.
Also, I see you are a Director of Manufacturing. Any chance to get some management related posts?
Another example of counter-clockwise flow is an aircraft carrier. With one exception every aircraft carrier ever built has had a counter-clockwise landing pattern. The exception, a Japanese carrier, was built to operate with a counter-clockwise sister ship. The theory was that each carrier would have it own opposing landing pattern that would allow them to sail close together in formation.
As it happens, pilots tend to abort landings by veering to the left. On a clockwise carrier, the superstructure is on the left side instead of the right, which is where aborting aircraft tended to crash.
The ship was rebuilt before the war with the tower on the “right” side.
Hi Brad,
Yes, I would say you are correct in your assumption. Thanks for the kind words as well. I will see what I can come up with on the management topic.
Hi Andy,
Thanks for the comment! I have followed your work for awhile and am honored you read my little blog. I didn’t know this about aircraft carriers. Thanks for sharing and commenting. Cheers.
Hi Ron – yes, I was taught the same things about counterclockwise and why that’s “correct.”
I also think that’s a rule that’s a good rule to follow unless it isn’t… as you were alluding to, I think there’s no substitute for thinking and for experimentation. That’s always better than blindly following rules.
Another more practical reason may exist…but we must consider the origin of workcells at Toyota. It may be that when Ohno, or a supervisor, experimented with flow in his machine shop he encountered a problem never faced prior to workcells: all lathes have their headstocks on the left side of the machine requiring operators to load stock with their right hand and tighten the chuck with their left. In a workcell manufacturing to JIT; parts were unloaded – the left hand placing the finished part in the bin to the left while picking up the stock for the next cycle with his right. My guess this efficiency in loading materials, (until auto bar loaders and through spindles replaced a machinists hands) was proliferated throughout Toyota and its keiretsu of suppliers. Counterclockwise workflow was the countermeasure for eliminating extra fumbling of the part between hands during load/unload cycles.
Often something that is innocuous becomes conventional wisdom. I literally have seen and heard lean consultants state that workcells MUST go counterclockwise for the right hand reason. It is almost taboo to suggest anything but U-shaped and counterclockwise. But I think most people, except those posting comments here, dismiss the taboo attitude and forget to understand why counterclockwise exists in the first place. Since the workcell is the most copied lean concept born from TPS than it only makes sense that something so copied for so long has evolved into a sacred cow in North American lean literature and practice.
The fact that the majority of the population is righty and may be a convenient and viable reason for not trying to make our workcells flexible, but how to explain right hand people doing things with their left hands everyday? Rolling down the driver side windows, typing, opening door handles, tying their shoes, using utensils, or juggling? Don’t believe me? Give your toddler who is learning to use utensils – toddler SAFE utensils please – a knife and fork. Watch them struggle with their non-dominant hand. Then you do the same and marvel at how easily it seems to you, how you don’t even think about it. Try to think about it as you cut your steak, slice a cooked carrot with ease between the tines of your fork. You can’t even think about it as it comes so naturally, right? The fact is, people can LEARN to use their left hands as well as their right and vice versa – with practice and discipline.
Of course, I don’t think I can prove any of this, it is just an educated guess based on experience, but I think its a pretty good guess. What do you think?
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