What’s the Conventional Lean Thinking on Direction of Flow?
I set up a few workbenches to form a U-shaped cell. Direction of product flow immediately came into question. Should the product flow clockwise or counterclockwise? A quick Google search listed Ron’s blog article from September of 2007 titled “Why Flow Counter Clockwise?”
Several great points in the article. A key point was about reaching with the right hand. As Ron explains:
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).
After reading the article, I accepted counterclockwise as being correct. It was after I set up the cell that I realized that it wasn’t the best option for me.
It’s Not About Direction
I’m not disputing Ron’s article. In fact, I agree with everything in it. There’s an important difference between the situation described Ron’s cell and mine. The difference is that I’m the only person working in my cell.
There’s an emphasis on the flow of material through the cell. The direction of flow isn’t the important factor in my view. The greater consideration is something Ron has also written about in the past: “What problem are you trying to solve?”
The motor skills and reaching for the next item are the reason for materials to flow counterclockwise in Ron’s cell. Those are also the reason for material to flow clockwise in mine. When material flows from one operator to the next, as Ron explains, reaching to the right for the next item is easier than reaching to the left.
When working in a cell alone, I’m moving through the cell along with the product while reaching to the right for the next item to add to the assembly. This required the downstream step to be to my right, meaning counterclockwise flow.
Why Is This Important?
What’s important is the thinking behind the tool and not simply the most common result from conventional wisdom. I did my Google search for direction of flow in a U-shaped cell when I should have known there could be reasons to go either way and tested both directions. The real issue wasn’t the direction of flow, but the ease of reach for the next item. Ease of reach is a factor in quality, speed, and cost.
Material should flow neither clockwise nor counterclockwise. It should flow in the direction that helps the operator(s) do the work easier, better, faster, and at the lowest possible cost.
Run the experiment and discover your obstacles.