A Guide to Implementing the Theory of Constraints (TOC)
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Project Buffers Critical Chain Implementation Multi-Project
This page contains some of the “pointers” needed to turn the knowledge in the preceding pages on Critical Chain Project Management into something that will produce both action and significant results for a particular case. As you know, people write books on just this aspect and it is not the intent here to provide yet another. But there are a number of small things, often very small things, that people who are not so familiar with Theory of Constraints might find value in. Things that we
might otherwise do that we shouldn’t do, and things that we might otherwise not do that we should do. It is one of those interesting things in life to see a “new” approach such as critical chain
applied in an “old” environment with many of the old assumptions and reactions – many of
which are so automatic that we don’t even think about them – and then to hear that the new
approach isn’t working. It’s not the new approach that is at fault, it is the old thinking of the old environment. We need to watch for this constantly.
The Good, The Bad, And The Ugly
Well, I don’t know about the good, but I’ve seen a bit of the bad and the just plain ugly. There are many companies who see themselves as generalized producers rather than “project” companies.
They make things with long touch times, for example tangible manufacturing or near-intangible
software, and yet have little explicit project management of their operation. Companies that build one-offs, either to a standard design or customized, tend to use the “last one like that” to estimate
effort in “the next one” and set start and finish dates around that. They then launch the new project into the system without due regard to the loading on the system because “the customer is waiting and every day is a day lost to him.” And so it goes.
Where there is some logistical control, oddly, it seems to be as a material resource planning system (MRP). I say oddly, because such systems depend upon queuing for their functionality and as we know there are no explicit queues in projects. Oddly too, because such companies
may see the age of their MRP system as the cause of their problems and embark on expensive and time consuming upgrades to let them know more quickly how fast they are losing money. They have addressed an effect rather than the underlying cause. Maybe people use MRP systems because they do know how damn difficult it is to organize anything around one of the Critical Path Method (CPM) software approaches, a difficulty brought about by the close coupled
dependencies (tasks) and localized safety.
Replacing MRP with Critical Chain Project Management is a fundamental step forward. There is a fine example of this from the United States Marine Corps that you can download (1).
We need to move from the bad to the good. In order to do so, we must do things that currently we do not do. We now know the logistical direction of the solution and most of the detail – Critical
Chain. Here, let’s examine a few more of the important implementation details, some of the
things that other people might forget to tell us about.
Basic Project Plans
Many manufacturing/service projects that are to some extent repetitive – the same or similar type
of thing is produced each time – have sort of “evolved.” Often no one has ever sat down and
asked the critical question about what needs to be done and when, and which parts must be
done in sequence and which parts can be done in parallel. People are far more likely to do
this for “unique” projects or very large projects, but when we have a significant number of
apparently simple and mundane or repetitive projects we often don’t do it at all. Of course if we sit down and redo this plan from scratch, then once it is done, we may not need to revisit it again; we have a template, but it will be a vastly improved template compared to the one that we previously carried around in our heads.
We need to sit down and take a long hard look at devising the minimal PERT chart that we need to
implement the project. Something like this.
A Simple Project
Task 4 Task 5
Task 1 Task 2 Task 3Task 6
The result is, as we have said, an “A” plant tipped on its side. Curiously, this is also Goldratt’s
Thinking Process logic diagram for pre-requisite trees;PRT； tipped on its side as well. A
pre-requisite tree deals with necessity-based logic – a tree with a trunk and main branches but not
with the sufficiency of all the sub branches and leaves, or a stick figure rather than something that is fully fleshed out (2). A discussion of these logical tools can be found in the section called Tool
Using a pre-requisite tree approach it is possible to build the logic needed for the PERT diagram. If we do so, then the following will occur;
Automatically Wherever Feasible
Task 1 Task 2
Tasks that are not true predecessors will be resolved out of the critical chain into parallel feeding chains where they belong. The overall length of the Critical Chain is therefore reduced before we
even start. This is already a significant competitive advantage.
Don’t fall into the trap of providing sufficiency, that is, breaking the basic tasks down into further detail. The people who are directly involved know what is required.
A common enough problem once a proper project plan has been produced is to try and resource it fully. Once again, we don’t need to do this. We only need to resource the tasks that we have to.
These are tasks where structural or resource dependency may mean we overload a resource for a
time, or where there is a resource or a group of resources who might, if not well managed, constitute an internal constraint.
Recent work by Ricketts (3), especially the concept of resource management and resource
buffering in service-type operations, including projects, is important and deserves widespread understanding. It is a significant move forward in Theory of Constraints knowledge.
Reducing multi-tasking in projects is akin to reducing work-in-process in manufacturing
operations. Although in manufacturing operations we certainly can increase the output of the constraint independently of the work-in-process, at least in the short term, ultimately failure to reduce work-in-process, and thus manufacturing lead time, will cause such an implementation to stagnate far short of its real potential, or more likely it will cause the implementation to fail.
In project operations we too can increase the output of the constraint, time, by reducing the critical
chain, but not independently of the work-in-process in multi-projects. Because the touch time is
so much higher in project operations compared to production operations we can’t even implement Critical Chain Project Management unless we reduce multi-tasking.
Although I have tried to keep things simple and focus on single project implementations, the real world almost always forces multi-project conditions upon us – even if it is a single project – by
virtue of “other things” that must be done, as well as the project. And if you think avoiding
multi-project is a cop-out, then just consider how many Critical Path Method explanations don’t even go near multi-project.
There are two aspects to multi-tasking. Goldratt makes them explicit (4, 5) but my experience is
that people confuse the two issues almost immediately.
1. In any multi-tasking multi-project environment there is a proportionate increase in individual
project elapsed time with increase in total number of projects. Simply stated, double the
number of open projects, double the length of any individual project.
2. Lack of a clear priority system between projects and tasks in a multi-tasking multi