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Old 09-28-2012, 06:33 AM
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Lots of S's and F's

I'm trying to figure out what the difference between a Finish-to-Start with a lead time and a Start-to-Start is?

Lets say we are digging a trench and laying pipes into that trench. Logic has it, we can't start laying the pipes until the trench is dug, ergo Start-to-Start. However, can't we achieve the same result with simply creating a constraint on the pipe laying activity as Finish-to-Start with a lead?

So why would we even need an SS relationship apart from having a nicely rounded off permutation of letter combinations i.e. FF, FS, SF and SS?
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Old 10-01-2012, 08:36 AM
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Management likes to see summary level schedules where work is represented by as few bars / tasks as possible. It gives them a quick idea of where they stand.

However, a rigorous CPM schedule for field execution would ideally have a greater degree of detail. Instead of one long task for "dig trench", you could segment the work into several smaller tasks:

dig trench 40 feet (section 1)
dig trench 40 feet (section 2)
dig trench 40 feet (section 3)
etc.

and similarly, segment the pipe laying:

lay pipe section 1
lay pipe section 2
lay pipe section 3
etc.

Now it is easy to schedule the tasks with FS relationships. Additionally, with a greater degree of detail, progress updates can be more accurate/reliable as there is less guesswork on percent complete for a given task in the schedule.
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