Backing into a task

[Tunamonster]

I am finding several cases where I want a task to end at the time another
begins. I have seen on the board here that to do this one copies the Start
date of one task and does a Paste Link into the finish date of another task.
A little clumsy, I think, but so far so good. My understanding is that once
such a link is established then Predecessors for that item are ignored. What
I want, however, is to allow a time lag between two so-linked tasks. I was
trying to figure a way to do with a 3rd milestone task but haven't quite
found it.

Here is the scenario:

We have a heating system that must be replaced for a house project, i.e.
converting from oil to gas. Now, we don't want to go without heat too long in
the house and we want the driving factor to the the gas installation
schedule. However, we will need to get the oil furnace out of the way before
we can put in the gas furnace. If RO is the remove oil task and IG is the
install gas task, then we want to have IG happen asap based on its
predecessors. We want the RO to be driven based on the IG task, but to
precede it. Finally we want to assure a short buffer of around 2-3 days but
not more between the end of RO and begining of IG.

If IG is scheduled to begin 3/20/09 based on its independent predecessors
we'd want the RO task, which takes 2 days for example, to finish 3 days
prior. That is, RO would start 3/15/09, last 2 days until 3/17/09 and then
have a lag/buffer of 3 days until IG is started.

So, how can this be done? I tried creating a task X that is a milestone and
Paste Linked the Begin date of IG to X's Finish date. Next I created a FS
depedency for X to RO with a 3-day lag time. I expected this to work, but in
fact RO is starting and ending more than a week before either X and IG.

 

[Rod Gill]

Experiment with a Start-Finish link. These let you schedule tasks backwards.

--

Rod Gill
Microsoft MVP for Project

Author of the only book on Project VBA, see:
http://www.projectvbabook.com

 

[Tunamonster]

Having thought about this a few minutes longer I realized that I could simply
make the milestone task a 3-day duration task and then Paste Link its Start
date into the Finish date of RO and that works fine.

So I will modify my question to be is this the best way to do it?

 

[Dave]

I am finding several cases where I want a task to end at the time another
begins. I have seen on the board here that to do this one copies the Start
date of one task and does a Paste Link into the finish date of another task.
A little clumsy, I think, but so far so good. My understanding is that once
such a link is established then Predecessors for that item are ignored. What
I want, however, is to allow a time lag between two so-linked tasks. I was
trying to figure a way to do with a 3rd milestone task but haven't quite
found it.

Here is the scenario:

We have a heating system that must be replaced for a house project, i.e.
converting from oil to gas. Now, we don't want to go without heat too long in
the house and we want the driving factor to the the gas installation
schedule. However, we will need to get the oil furnace out of the way before
we can put in the gas furnace. If RO is the remove oil task and IG is the
install gas task, then we want to have IG happen asap based on its
predecessors. We want the RO to be driven based on the IG task, but to
precede it. Finally we want to assure a short buffer of around 2-3 days but
not more between the end of RO and begining of IG.

If IG is scheduled to begin 3/20/09 based on its independent predecessors
we'd want the RO task, which takes 2 days for example, to finish 3 days
prior. That is, RO would start 3/15/09, last 2 days until 3/17/09 and then
have a lag/buffer of 3 days until IG is started.

So, how can this be done? I tried creating a task X that is a milestone and
Paste Linked the Begin date of IG to X's Finish date. Next I created a FS
depedency for X to RO with a 3-day lag time. I expected this to work, but in
fact RO is starting and ending more than a week before either X and IG.

Try linking IG to your milestone with an SF link and a -3 day lag.

Then copy the start date of the milestone and paste it as a link to the
finish date of RO.

 

[Dave]

Having thought about this a few minutes longer I realized that I could simply
make the milestone task a 3-day duration task and then Paste Link its Start
date into the Finish date of RO and that works fine.

So I will modify my question to be is this the best way to do it?

It's not best practice because the 3-day duration task implies that
there is work to be carried out during that period.

 

[meg99]

It's not best practice because the 3-day duration task implies that
there is work to be carried out during that period.

Why not use a SS-5d? Link RO to IG with SS-5d (with IG as the pred to
RO). Thus if IG finishes early (say 3/19), then RO will show a start
5 days prior. If IG is delayed a couple of days (say 3/22), then RO
move to the right but will still show a start 5 days prior to IG.

meg99

 

[Tunamonster]

I tried what you suggested, but I have to say that I had a hard time with
removing the existing paste-links I'd put in the various finish dates so I am
not sure that it is not the reason what you suggested didn't seem to work for
me or not. Or maybe I misunderstood your instructions.

In any case, I did take your idea of the -3lag time and did it this way:

RO - SF w/ X -3d lag
X Milestone - SF w/ IG
IG - no dependencies except external ones to the discussion here

This seems to work. Is that *supposed* to work or do I have some sort of
leftover issue from the paste-link problem I mentioned above?

 

[Tunamonster]

Actually seems I don't need the milestone task at all. Just making RO have
SF-3 with IG seems to work fine. Is it so simple after all?

 

[meg99]

Actually seems I don't need the milestone task at all. Just making RO have
SF-3 with IG seems to work fine. Is it so simple after all?









- Show quoted text -

Tunamonster,
Just a note or caution about SF tasks. The problem with SF is that it
can easily cause a loop. You might not have a problem for a while but
in a modestly complex project, you could add tasks and links and get a
message that you have a loop. If that happens, you need to open the
predecessor field and look for the SF task. It can get a little
thorny trying to run it down.

meg99

 

[Dave]

Why not use a SS-5d? Link RO to IG with SS-5d (with IG as the pred to
RO). Thus if IG finishes early (say 3/19), then RO will show a start
5 days prior. If IG is delayed a couple of days (say 3/22), then RO
move to the right but will still show a start 5 days prior to IG.

meg99

Because it's not enough that RO starts on the right date. If it
overruns, it must delay IG. Consequently, the finish date of RO must
drive the remainder of the work.

 

[Dave]

You haven't solved the problem you originally stated.

The problem you originally posed was how to make tasks start and stop
simultaneously. That is actually bad scheduling practice, but
nevertheless, sometimes you have to do it.

With your link, what you have done is say that RO cannot finish before 3
days before IG has started.

However, it can finish afterwards. Drag the RO task forward in time and
you will see that you can actually make the entire RO task start after
IG has finished and IG will not move.

You need to understand that links don't determine when tasks will start
and end. Rather they drive what must happen in order for other elements
of the work to take place.