Drum Buffer Rope Part 2

In Part 2 of my blog series on Drum Buffer Rope, we will dive into variation.  That is, how variation impacts your system and how DBR manages it.

Variation

For years, if not decades, people and organizations have dedicated considerable time and effort to remove variation from systems.  The utopian goal is to remove as much variation as possible from the system.  No matter how much planning is employed, no matter how much effort is extended, the bottom line is that variation will still exist. If you were asked how long it takes you to get to work every day, your response might be something like, “about thirty minutes.”  The instant you answer with the word “about,” you have introduced variation into the system.  You  know that historically speaking, some days you get to work in twenty-five minutes and yet others days it can take thirty-five or forty minutes.  In your “get to work” system, things can happen that will either speed up the process or slow it down.

Variation exists in everything, especially within a system. You understand that some processes will produce at a faster or slower rate than others, and this is the premise behind variation. Because of variation, the output from a system will not be linear,but rather it will operate within a range that changes.  This variable range is known as statistical fluctuation, and it exists in every system.  It’s important to understand that you cannot make variation go away.  The theory and practice of Six Sigma has pioneered the race to reduce variation.  But even with the most valiant efforts of time and money, not all variation can be removed.  You can reduce the amount and severity of variation, but it will still exist.  Once you understand that variation is a constant variable in any system, it’s easier to understand that at some point you will reach the minimum variation that is controllable in the system, and any efforts to reduce variation beyond that point are typically fruitless.  Perhaps, instead of spending so much time and effort on techniques to remove variation, the focus should really be on techniques to manage variation.    

Managing Variation with Drum Buffer Rope (DBR)

When viewing a system through the eyes of DBR, it becomes quickly apparent that improving every step in the process is not required, nor will the sum total of all of those discrete system improvements equal an improved overall system.  When conducting a full systems analysis, with the intent of implementing DBR, an important consideration to know and understand is the location of the system constraint, or the slowest operation.  In Goldratt’s Five Focusing Steps, this is Step 1—Find the constraint.  Once you know where the slowest operation resides, you now have the information necessary to know where to focus your attention within the system.  Why is it important to understand where the slowest operation is?  Because this is the location that controls and determines the output for your entire system.  In essence, the entire system will produce no faster than the slowest operation can produce.  (The system can produce less, but it won’t produce more.)

With the constraining operation identified, you have collectively quarantined the “drum beat" for your system.  Knowing the drumbeat is of strategic importance to implement and gain any system improvements.  The drum provides you with the necessary information of knowing where to focus your improvement efforts.  Historically, many organizations can and do conduct many improvement projects on a yearly basis.  The mantra seems to be that every organization and every process should strive for improvement.

The thought is that each organization is improving at some level of frequency to make the whole system better.  However, the sum of many efforts does not always equal what is good for the whole. The problem with this type of thinking is it is a totally unfocused shotgun approach to solve the problem.  In effect, it presents an improve-ment policy that states: "If I select a wide enough range, then I should hit the target, or at least come close to the target."  When you take the shotgun approach you might hit everything a little bit, but miss the full impact required to make real change and improvements.  If your shotgun approach includes trying to improve non-constraints, and many do, then the system as a whole gains nothing!

The improvement of non-constraints in isolation of the entire system, without a comprehensive analysis, is just a way of dealing with symptoms and not the real issue (constraint).  Without the ability and the accurate information necessary to focus on the real issues, the disease goes merrily on.  Improvement of non-constraints is a noble gesture, but one that yields little, if any, real improvements.  Every process within a system does not need to be improved at the same time!  Some system processes are more important than others.  Without knowing where your constraint resides, your efforts to improve will be unfocused and many times worthless, serving only to consume large amounts of money, resources, and time.

In my next post we will continue with our discussion of managing variation especially as it applies to Drum Buffer Rope.