Lag/Lead Time

[bkoren]

I have 2 tasks: Task A and Task B

Task A takes 90 days
Task B takes 66 days
Task B must start 21 days after Task A but cannot end until after Task A is
finished.

How do I set up the depencies on these tasks?

I appreciate any assistance.

Barb

 

[Jan De Messemaeker]

Hi,

The blunt answer is you can't
These atsks are probably too general.
If you cut them (at least B) into smaller pieces you can.
HTH
--
Jan De Messemaeker
Microsoft Project Most Valuable Professional
+32 495 300 620
For availability check:
http://users.online.be/prom-ade/Calendar.pdf

 

[Chicago2Paris]

Can't you do a FF+21d? Assuming "A" starts on 1/23, that means "B" would
start on 3/27 and end on 6/26 after "A" ends on 5/28...

 

[bkoren]

Maybe I am not clear on how the lag time works with finish dates but doesn't
FF+21d mean that Task B would finish 21d after Task A finishes?

 

[Chicago2Paris]

Yep, it can't be done unless you do what Jan mentions...

 

[Jim Aksel]

Allow me to expand on Jan's answer and offer some other observations.
The way I see it, you want task B to start 21 days after the start of Task
A. Let me know if I am wrong. Task B cannot finish until task A finishes.

Now look at your durations. 21 day lag + 66 days of duration for Task B has
to be at least as much duration as Task A but it is not. A duration is 96,
the total on B is 21+66 which is 87 using my math. So that will not work on
the face of it.

Let's try Jan's approach. Add a milestone betwen A & B and call it anything
you like, I will call it C. So the task order is ACB. Link as follows:

Predecessor for C is A SS + 21days.
Now make Task B a hammock task with a start date the same as C start and a
finish date the same as A finsih.

You can read about Hammock Tasks here: http://project.mvps.org/faqs.htm
You want to read FAQ #19 Hammock Tasks.

As a note, I challenge your logic that a task cannot start for 21 days after
the start of another. As Jan said, you are missing details. Something
happens during that 21 days that will tirgger B to start. Even if it is "Let
speciman grow in test tube for 21 days." Even so, those are elapsed days not
business days.

--
If this post was helpful, please consider rating it.

Jim Aksel, MVP

Check out my blog for more information:
http://www.msprojectblog.com

 

[Jan De Messemaeker]

Hi,

Let me be a bit clearer.
The point is - referring to your original question - that you can't have two
links between two tasks.
You cannot have both start and finish links.

This being said, if you cut B into B1 and B2, you can have a link A-B1 (SS +
21d) but still this would mean B1 cannot start before that date, links NEVER
NEVER mmean MUST START ON. Never.

Then link B1 to B2 simply FS.
Now link A to B2 FF; then indeed B2 will be planned not to end before the
end of A.

HTH

--
Jan De Messemaeker
Microsoft Project Most Valuable Professional
+32 495 300 620
For availability check:
http://users.online.be/prom-ade/Calendar.pdf

 

[bkoren]

Jim, Jan,
I like the idea of adding the milestone as you suggested. I will look up
how to do hammock tasks.

I appreciate the comments about missing details. Yes, I do realize that
there are many details omitted. I am trying to do some forecasting of
projects and some What-If scenarios in an attempt to obtain some target
dates. There are certain high level tasks that I need to include to get
realistic numbers. This is NOT for an actual plan that I will use to track
projects.

Thanks for you help. This group has never let me down!
Barb

 

[vanita]

Hi Barb

What you require is a very practical requirement on projects. In such
situations we follow these steps:
1. At planning stage link A and B with the link type SS+21 days. So. task B
would be now scheduled to be started 21 days after task A.
2. At execution stage, when task B has actually started and you
assign'Actual start' date to task B, delete this SS link as it has served its
purpose and chage it to appropriate FF link because now task B can not finish
before task A. If due to some reason remaining work on task A gets delayed,
work on B should also be slowed down.

I hope it helps.
Vanita