Let me ask you a question. Is a moving constraint/bottleneck a good thing or bad thing?

I contend it’s a good thing. No, I contend it’s a great thing. Allow me to explain.

Let’s say there are three processes in your widget making factory – machining, painting, and assembly.

After your current state value stream mapping exercise you learn that machining is the constraint to the system due to a variety of reasons (e.g. cycle time, defects, availability losses, etc.).

Once this is understood you and your band of merry men (and women) attack these issues with reckless abandon. After a few weeks of focused kaizen, machining is no longer the constraint – assembly is.

In fact, if you are able to increase the output of assembly you will immediately sell more since your sales growth has gone through the roof due to your already best in class lead-times.

So, as you probably guessed, your team heads over to assembly with stop watches and video camera in hand. You study things and identify lots of excess motion, poor material presentation, and ineffective planning of the cells.

A few weeks later, assembly is rolling along like a well oiled machine… and wouldn’t you know it… that darn painting process is now the bottleneck!

I could go on and on with this post, but I think you get the point.

You see, I contend that moving constraints mean your business is in constant growth mode. And this constant growth is placing constant pressure on your manufacturing capabilities.

Conversely, if you work to balance your cycle times to takt time and that suffices for more than six months, I’d contend you are not growing your business.  And that, as they say here in Texas, ain’t good.

Do you agree?

Last night we discussed the main tenets of TOC. Tonight we will introduce the Lean Pacemaker showing how it may not always be the constraint in our system. This, my friends, is where the TOC and Lean proponents often “bow up” and butt heads a bit.

Lean Pacemaker

In a Lean system we normally want to schedule production at one process. This process, called the pacemaker, is normally towards the end of the line (sometimes final assembly). The basic idea is that we schedule production at this pacemaker allowing it to then “pull” material to it. A key rule for selecting the pacemaker is that all processes after it must “flow” to the customer.

The Debate

The debate over TOC Bottlenecks and Lean Pacemakers is best summarized by John Shook. I have never met John but have read much of his writing and can safely say he has likely forgotten more about Lean than I will ever know.

I came across an article on the LEI website awhile back where John explained some of the key differences between Lean and TOC. You can find the full article here. I will quote a portion of this article below as it summarizes the point I am trying to make perfectly.

Secondly, there is a fundamental difference between TOC “bottlenecks” and TPS “pacemakers,” though they are frequently misunderstood to be roughly analogous. What is analogous is that TPS, like TOC, strives to identify and “break” bottlenecks. But, TPS does not allow a bottleneck to set the pace of the value stream. After all, the bottleneck may exist for any number of problematic reasons – excessive downtime, poor quality, long changeover times, etc. Why would I choose to let an operation with such problems determine the way I flow my entire value stream? Of course, I have to deal with the problem operation (the bottleneck), and there are numerous techniques to do so, but I will not let it dictate the pace (takt) of my entire product flow!

Which Method is Right?

I personally believe in the end TOC and Lean practitioners are actually teaching very similar things. Let me explain.

Both Lean and TOC teach that bottlenecks must be broken. In a Lean system we know that if a process cycle time is greater than takt time we have an issue that must be resolved. This is roughly analogous to the TOC step of “elevate the constraint.”

Also, drum-buffer-rope is very similar to the Lean pull system. Sure there are some differences but the concepts are close.  However, as Mr. Shook explained a Lean system will not allow a bottleneck to automatically be the pacemaker for the reasons he explained.

I must admit, I personally agree with Mr. Shook on this point. It makes little sense to me to allow the chubby kid to set the pace. As Jon Miller commented after last nights post, we should help Herbie lose weight!

And while they may not admit it, I really believe most TOC proponents believe the same thing. They just explain things a bit differently.  I hope this helps explain some of the differences and similarities between TOC and Lean.  Hot sports opinions are of course very welcome by clicking the “comments” link below.

Tonight I am starting a 2 part series contrasting the Theory of Constraints with Lean Manufacturing. Specifically, I want to discuss the differences between a TOC “bottleneck” and a Lean Manufacturing “pacemaker.” I have seen TOC proponents and Lean Manufacturing proponents go to blows over this topic. I hope to explain the differences (yes, they are different) while explaining how I believe we as continuous improvement practitioners should move forward leveraging the strengths of both concepts.

The first part of the series (tonight) will be all about TOC. Tomorrow night I will cover the Lean side of things.

Theory of Constraints Overview

Theory of Constraints (TOC) is a management philosophy developed by Dr. Eliyahu Goldratt, a physicist. TOC popularized after the release of the 1984 best seller “The Goal.” To this day this book is one of my all time favorites. I even have it on mp3 and listen to it in my car from time to time… yes I know, I have issues.

In “The Goal” we meet Herbie who is an overweight child who holds up the rest of his friends during a hike through the woods. The boys formed a human chain so the leader could keep track of them all. Herbie, poor lad, was in the middle of the pack which soon created some issues for all involved. The faster kids in front of Herbie ended up way ahead of the pack while all the kids stuck behind Herbie were frustrated as they had to wait on him. The scout leader (and plant manager), Alex Rogo, fixed the situation by moving Herbie to the front of the line which set the “pace” for the rest of the kids. Soon after moving him there they removed all kinds of junk from Herbie’s back pack. This helped Herbie go faster which made the whole system (boys) move faster. This story summarizes the main ideas behind TOC. Specifically, you can also explain TOC this way:

1. Identify the constraint (your bottleneck or the thing slowing you down)
2. Decide how to exploit the constraint (make sure the constraint is only working on the things it needs to do and not other stuff)
3. Subordinate all other processes to the constraint (don’t let any other process work ahead of the constraint)
4. Elevate the constraint (speed the constraint up, i.e take the junk out of Herbie’s back pack)
5. If the constraint moves, which it often does, return to Step 1 and repeat.

Drum-Buffer-Rope

TOC teaches a concept called drum, buffer, rope (DBR). The main premise behind DBR is that the drum is the constraint or bottleneck in the system. It sets the pace for all other processes. The buffer is inventory that is used to protect the drum. Dr. Goldratt often speaks of “Murphy” (Murphy’s Law) who likes to strike at the worst time messing everything up. Thus, buffers are used to ensure our constraints and other key areas are never starved for work, even if Murphy strikes. Lastly, the rope is the scheduling or work release mechanism that gets everything moving.

If DBR sounds similar to some concepts Mr. Ohno taught 50+ years ago you are correct. However, there are some differences when you look into the fine print which we will discuss tomorrow night!

Other TOC Resources

Dr. Goldratt has written many other books which explain additional TOC concepts. If you are interested just Google it and you will see what I mean. His book “Critical Chain” is a super Project Management book.