Setting tasks to fix duration moves the start & finish dates

[Neil]

When I go from a "fixed work" on my tasks to a "fix duration" it will move
my tasks out ever so slightly which by itself is ok but when you add them all
up (2500 lines) it shifts my critical path out 8 days.
I'm trying to clear all costs, resources & work out to supply someone with
the schedule and need to my critical path as is. I have tried "effort
driven" or not, I have applied constraints and deadlines All with no help.
Any suggestions ?? I'm using PJ 2002 Professional
Thanks,
Neil

 

[Steve House [Project MVP]]

I don't know why simply changing the task type would affect the duration
unless you are making other edits as well - task type simply has no effect
unless you are editing something that changes work, units, or duration for
the resource assignments amd without seeing your plan it's really impossible
to say exactly what is causing the behavior you observe - but there's
something else in your post that needs commenting. You sound like you feel
the critical path is something the project manager has direct control over
or gets to choose and that's simply not true. The critical path is that
chain of tasks that determines the overall project duration - it is a
read-only calculated value based on the task durations and their linkages -
and is simply the longest sequence of events in the project. If you have
several pathways through the project from start to finish, the critical path
can easily change many, many times as the schedule evolves or as work is
performed. So in that sense there is no such thing as "my" critical path,
there is only "the" critical path and it is determined 100% by the amount of
work required to complete each task and the way you have structured the work
in the project. It is an output, not an input. It's length is simply the
length of time it will take you to do the project if you do the work as you
presently have it scheduled. If that's unacceptable, for example it puts
the finish past a contractually required deadline, that's telling you that
you need to revise the work plan so those tasks along the critical path get
done in a little shorter period of time or perhaps get done in a different
sequence if it's possible to do so. Of course, if you've made all the tasks
fixed duration that says that no editing of the resources will change their
durations. But shortening the critical path requires you to reduce task
durations. That means it will be incredibly difficult to get the project
done any quicker than your present critical path is telling you it wil take.
Something's gotta give.

 

[peterdelorme]

Steve:

I'm one of those who thinks 'I' control the critical path; which in effect I
do by determining the efforts, durations, starts and finishes as I create the
plan.

My question is, how do I add or delete a task from the critical path, after
it has been calculated?

 

[Mike Glen]

Hi Peter,

Welcome to this Microsoft Project newsgroup

If you want to delete any task, critical or not, just select it and delete
it. The critical path(s) will then be re-calculated by Project and, most
likely, will change significantly. If you're not sure how the critical path
is calculated, please see FAQ Item: 42. Guide to Network Analysis.

FAQs, companion products and other useful Project information can be seen at
this web address: http://www.mvps.org/project/

Hope this helps - please let us know how you get on

Mike Glen
Project MVP

 

[Steve House [Project MVP]]

The only controls you have on the critical path are indirect controls where
the path is affected by the decisions you have made regarding task
sequencing and their durations if, and that's a very big "if," you can
actually control the duration. IF a painter can apply paint at a maximum
rate of 10 square feet of wall per hour, you have 250 square feet of wall to
paint, and only one painter to do it with, that pretty well puts that task
duration out of your control - it's going to be mighty close to 25 man-hours
of effort required and the duration will be 25 working hours if the painter
is fully committed and more than that if he only can devote part of his
energy to that specific task.

As Mike said, there is no difference in deleting a task on the critical path
from deleting one that's not on the critical path - you simply delete it.
Adding a task is equally simple but it may or may not end up a critical task
or on the critical path. IMHO, task linkages are dictated by the nature of
the physical processes involved in creating the task deliverables. Erecting
walls is a predecessor to installing rafters not because we want to
structure the work that way but rather because the law of gravity doesn't
give us the option of setting the rafters in midair and then stuffing the
walls in under them later. Another rule is that all tasks in the project
will have at least one predecessor and one successor, except for the start
and the end milestones. If a task has no other direct successor, it will
still have the finish milestone linked to it. When your project is
structured like that you will find there are usually multiple paths leading
from the start to the end - one of them will be the longest of the
alternatives and that is the critical path by definition. If the task
you're adding belongs in that sequence due to the nature of the deliverable
inputs it requires and the outputs it produces, it will add to the critical
path. If it doesn't fit into that sequence of operations according to the
nature of the physical process itself, then it doesn't add to the critical
path. That's why I say you don't choose it - the structure of the project
is pretty well something that is dictated by the nature of the work
processes and as a PM part of our job is to discover the most efficient way
of getting it done. Notice the operative word is "discover." It is a
process of discovery, not an imposition of our will. Our will comes into
play when we're defining the goals but once we decide what we want to
achieve, we then discover the best way of achieving them.

--
Steve House [MVP]
MS Project Trainer & Consultant
Visit http://www.mvps.org/project/faqs.htm for the FAQs