ALAP constraint behavior question

Thanks SO MUCH Tom.    I'll give that a try in my full schedule and report back.

JB

Much appreciated Tom.  Your idea was a great workaround and in many instances worked great in my schedule.  I had a few places where there were predecessors to the Activity 2 you helped me with and those predecessors had the same issue but without the same solution available.

I finally found this blog entry where a user wrote a MP VBA macro that whips through, finds all the instances where you want the ZFF (zero free float) behavior and replicates it programatically (using the ugly 'C' word).  I modified it slightly to meet my needs and it really works great, so until I can afford Primavera, this will have to do

http://www.boyleprojectconsulting.com/TomsBlog/2016/08/31/simple-macro-for-imposing-zero-free-float-constraints-in-microsoft-project/

Thanks again.

(LOL -- just realized that it was YOUR blog I just posted.  So DOUBLE thanks and best wishes during the upcoming hurricane headed your way - stay safe.)

JB

 

I'm glad you got it worked out.

Sorry I didn't think to mention that macro, which I don't use much.  Maybe I would use it more if it were improved by combining it with a longest-path-type backward logic tracer.  As it is, I've become less reliant on ZFF constraints over the years - in both MSP and OPV - so it's not worth the time to improve the macro.

Hi John,

The behavior you seek is that of a Zero-Free-Float constraint, which is not available in MSP.  When used in a forward-scheduled project, the ALAP constraint in MSP is in fact a Zero-Total-Float constraint, which serves no useful purpose as you have found.  Though my memory is a bit fuzzy on the earlier versions (and I skipped from Project '98 to Project 2003), I'm pretty sure MSP has never had a ZFF constraint.  The workaround, at least where Task 2 represents a just-in-time delivery, is to insert a readiness milestone between 1 and 3.  Then make that milestone an FF predecessor of 2.  This keeps the logic flow intact without using the C-word.

Zero-Free-Float constraints are certainly available in other scheduling software - P3 actually called it by that name.  P6 calls it ALAP, which of course causes much confusion for P6 user who stumbles into MSP.  I think Asta Power Project allows entire strings of activities to be similarly delayed within available free float - pretty flexible.      

I'm not sure if PP has fixed its image retention problem (uploads like yours were only retained for a couple hours).  If not, I'll move the image below (including the workaround) to an external host. Good luck, tom

(18Sep'18 - changed image link to external source.)

Hello Tom and John,

Marco,

Thanks for the comment, though I would disagree with your characterization of MSP as a "poor and amateur application."  I would say it's a reasonable scheduling application with some pluses and minuses - primarily aimed at a "poor and amateur", but extremely large, user base.

Rgds, tom  

Hi John,

Wouldn't it be possible, to simply run Activity 2 with a relation type FF to Activity 1? 

Abel:  // "Wouldn't it be possible, to simply run Activity 2 with a relation type FF to Activity 1? " //

Not and get the desired result - I dont' want Activity 2 to be scheduled to finish with Activity 1, I want its finish to be tied directly to the start of Activity 2 with no float ever.   

Logic: (part of the confusion may be a typo in my OP -- fixed here)
 

1: The finish of Activity 2 as late as possible relative to the start of Activity 3

2:  The start of Activity 3 as early as possible relative to the finish of Activity 1

As Tom has accurately described it, it's a 'just in time' scheduling issue.  

Tom's Macro has worked marvelously btw. 

JB

Hello Planners,

I would use a Start to Finish link between the activities 3 (Predecessor) and 2 (Successor)

By doing so, the activity 2 would finish at the begining of activity 3, and would not push activity 3 ahead against the milesone

This is the best workaround in MSP, whatever the version you are using .

Alexandre

Alexandre,

If your only objective is to manipulate the dates to get what you want, then the reverse logic and SF link may be OK; it seems common enough among MSP users of all experience levels.  It is nonetheless a misguided approach in logic driven planning, in my opinion. 

Equipment must be delivered before it is installed - full stop.  To discard this requirement and insert the SF link as you suggest is to damage the proper logic flow through the schedule.  As a result, the late dates and Slack of activity 2 (delivery) and its predecessors (e.g. specification, PO, design, production, etc.) are incorrect.  Moreover, the correct scheduling (early dates) of activity 3 (installation) and its successors is not assured in case of a delay of the equipment.

Tom,

you are perfectly right, SF link is only a workaround; it does not answer the fundamental question of the difference between Total Float or Free Float being used in the so called ALAP constraint

I will have a try to your VBA macro

Alexandre