LINK CONSTRAINT

[John]

We need to manage a link between two tasks with a hard constraint. At a set
time from start of first task we need to start another task. We CAN simulate
this by using a negative lag finish to start link. If the first task is re
scheduled / start date changed subsiduary task keeps its relationship. But if
the subisudry task is rescheduled out (to the right) relationship is not kept
i.e. the negative lag is only constrained in one direction. This means the
relationship can be broken by mistake.

John

John,
First of all it doesn't sound like you have a hard constraint. A "hard"
constraint is something like "must start on" or "must finish on".
Perhaps what you want is a hard link relationship that will allow an
adjustment to the start of either task to move the linked task. Project
does not support that type of link but you could try the following
workaround.

Let's say the tasks are 1 and 2 and you need the second to start 10d
after the start of the first task. First set up a Start milestone. Link
task 1 in a simple finish-to-start relationship with the milestone. Link
task 2 as: [milestone ID]ss+10d. Now, don't mess with the start date of
either task, instead adjust the milestone date as necessary. Both tasks
will move in unison while the delay relationship is maintained. Perhaps
not exactly what you want, but it will get you there.

John
Project MVP

 

[John Boy]

We need to manage a link between two tasks with a hard constraint. At a set
time from start of first task we need to start another task. We CAN simulate
this by using a negative lag finish to start link. If the first task is re
scheduled / start date changed subsiduary task keeps its relationship. But if
the subisudry task is rescheduled out (to the right) relationship is not kept
i.e. the negative lag is only constrained in one direction. This means the
relationship can be broken by mistake.

John

 

[Steve House]

Links are permissive critters - they specify the time after when the
successor task is allowed to start, not when it WILL start. There will
always be factors that can influence its start and make it later than
the link says it should. Suppose task B was supposed to start 2 days
after task A and task A started Monday ... task B should start on Wed
according to the link but suppose when Wed came around the only resource
qualified to do task B called in sick? There's no choice but to delay
it and Project recognizes such realities.

Think of predecessor as meaning "controlling" and successor as meaning
"controlled." The start of task A plus a 2-day delay is what permits
task B to start, so task B is scheduled to start 2 days after A starts
if it otherwise possible for it to start then. So the link between the
two tasks is Start-Start with a 2 day lag time.