SF relation

Dana,



The start-finish relationship is very seldom used and I read in a book that it has even been dropped from some of the project management scheduling software packages.



From my personal experience, the possibility to use this relation increases when you are working on master or baseline schedules (not very detailed) and will be absolutely unnecessary and easily avoidable in detailed schedules. Let me give you an actual example to simplify this:



For some contractual reason, I was required to introduce a new finish milestone called “PRE-COMMISSIONING & TESTING COMPLETION” into a master schedule that had general type of activities like:



“SUBSTRUCTURE”, “SUPERSTRUCTURE”, “FINISHING”, “ELECTRICAL WORKS” … etc.



As Frank mentioned below, I could have used FS with the Zero Free Float constraint with the “ELECTRICAL WORKS” activity but I faced two reasons why not to do that:



1) It is forbidden to use zero or negative float in the contract specifications of the project I’m working in.

2) The duration for the “ELECTRICAL WORKS” activity is 70 days and the milestone should “occur” after 50 days from the start of the activity. So the SF relation can be used to show the milestone finishing 50 days after the start of the activity (SF+50)



However, on the submittal of the detailed schedule, the SF relation is automatically removed when I presented the string of activities that will last for 50 days before the “PRE-COMMISSIONING & TESTING COMPLETION”.



I believe the SF relation is mainly used by contractors to make “work-around” solutions which is smart interpretation for “manipulation and fooling” the schedule reviewer.

Frank



A rare visitor, good to c you in the forum posting.



Can you give us an example that have to use SF in a Critical Path. (I read a book some years ago with a good example but the memory is loss)



Alex

I would use a FS with the Zero Free Float constraint instead of the SF relationship. Will give you the same result and avoids the out of sequence conditions once you update the successor in the SF relationship with an actual date.



I avoid using SF relationships.

Dana,



The Pred. of Task 2 is Task 3 with a SF relationship.



Task 2 is linked to Task 3 SF so that Task 3 drives the start of Task 2. Task 1 is linked to Task 2 SF so that Task 2 drives the start of Task 1.



Task 1 & 2 do have to complete prior to Task 3 starting but Task 1 & 2 do not have to wait for Electrical design to be complete. As soon as the scope of work is finalized Task 1 can start. The reason for the SF relationship is that I do not want Task 1/2 to start as early as possible in fact I want it to begin as late as possible as long as it is does not push the start of Task 3. I am not sure this is the best way to accomplish this but it has worked for me in the past.



Below I tried to clarify my logic





1. System Modeling - Task 2 (SF)



2. Check Modeling - Pred. Task 3 SF)



3. Develop Relay Settings - Pred. is Electrical Design(FS)



4. Check Relay Settings - Task 3 (FS)



5. Duplicate and Transmitt Relay Package - Task 4(FS)

Dana





Why make things complicated by using SF relationship. We can easily make our schedule by avoiding SF relationship.

Gents



I read that only very few conditions that you will need to use SF (Start Finish) relationship in a CPM plan. In addition, you can replace the SF relationship with the other three relationship type.



Good Luck



Alex

SF (Start Flag), considered to be a constraint, will accept ONLY Finish to Start relationships. Can be used to signify the beginning of a group of activities, and P3 automatically updates them according to the activities linked to them. Hope this helps!



--Dapo

Dana,

In my template I have a SF relationship on the following activities.



1. System Modeling - Pred. is Check Modeling



2. Check Modeling - Pred. is Develop Relay Settings (SF)



3. Develop Relay Settings - Pred. is Electrical Design



4. Check Relay Settings - Pred. is Develop Relay Settings



5. Duplicate and Transmitt Relay Package - Pred. is Check Relay Settings.



Task 3 is the driving task in this sequence. Task 3 cannot start until Electrical Design is complete. Task 1 and Task 2 can begin as soon as the scope of work has been finalized and must be complete before Task 3 can start. The problem I had was I do not want task 1 and Task 2 to be done weeks or months prior to the start of Task three. By linking Task 2 SF with Task three, Task 3 drives the start date of Task two and Task Two Drives the start dates of Task 1. I am not sure if this was the intended use of this relationship type but it works for me in this case. Hope this helps.