In my project, I have dozens of summary tasks which are comprised of sub-tasks of different durations. e.g.


Phase 1

SubTask1a --> d1

SubTask1b --> d2

Phase 2

SubTask2a --> d3

SubTask2b --> d4 Phase 3

SubTask3a --> d5

SubTask3b --> d6

Req #1: All tasks are sequential, i.e. Subtask1a has to finish for Subtask1b to start. Subtask1b has to finish for Subtask2a to start. Subtask2a has to finish for Subtask2b to start. Subtask2b has to finish for Subtask3a to start. etc

Req #2: All my summary tasks should have the same start date for their Phase 2. This means that depending the duration of phase 1, some summary tasks should start sooner than others.

Req #3: I can control only when phase 2 starts. The start date of phase 2, defines when phase 1 and 3 also need to start. So basically I need to have all my SubTasks-2a to start on specific date X. Alternatively I could have all my Subtasks-1b to finish on specific date X. I do not mind which approach to take.

PROBLEM I face: During the project, I will be asked to change the phase 2 (SubTask2a) start date many times, so I need my planning to be flexible and for phase 1 and 3 to adapt automatically to the changes without any alterations in their durations.

For example, if I move SubTask2a by 5 days in the future, then I would like all tasks of phase 1 and 3 to also be shifted respectively 5 days in the future. Similarly if I move the start date of SubTask2a 5 days in the past then phase 1 and 3 should also move respectively 5 days in the past.

I am struggling to find how the dependencies should be defined. I have tried many things but nothing really does the job. I would like to NOT use a "Must Start or Finish On" constraint because I want to be able to change the date X many times and I would like not to have to manually update hundreds of tasks. Also I do not wish to use any lags as my tasks durations are precise.

I attach an image my_gantt chart problem illustrating my exact problem. With the dependencies I have currently set up, I am trying to synchronise all my phases 2 with an external millestone date. If I move the millestone "PICK UP DATE" in the future or in the past, then phase 2 and 3 are shifted correctly. However phase 1 does not move at all! How can I fix this?

Let me know please if you have advice on how to handle the dependencies for that.

Thank you Nantia


1 Answer 1

  • Set up a driving milestone called "Phase 2 Start" and make it Must Start On [the date you want Phase 2 to start]
  • Make that milestone a predecessor of all the Phase 2's in your plan
  • Make all your Phase 1s a predecessor of that milestone using SF (start to finish)
  • Within each Phase 1, make the first task (e.g. SubTask1a --> d1) As Late As Possible

Now you can move the Phase 2 start date as much as you want and everything else will move with it, with the Phase 1 tasks always backloaded, but never exceeding the Phase 2 start.

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