Start No Earlier Than (SNET) constraints in Microsoft Project are helpful for modeling external constraints, such as delivery of material. But you may want to add a constrained milestone to properly assign accountability for delivery related schedule slippage.
External dependencies are dependencies that are outside your control. The classic example of an external dependency is delivery of manufacturing materials. In the blog Microsoft Project 2013 & Start No Earlier Than Constraints we inserted a SNET constraint on a manufacturing activity to constrain the start date until delivery of material.
This constraint worked well to demonstrate the importance of material delivery on the manufacturing effort. However, if we also want to show slippage accountability we need to insert a milestone for material delivery receipt.
This article demonstrates how to insert a milestone and constraint in Microsoft Project to highlight the importance of material delivery and document slippage accountability.
Our demonstration schedule is displayed in Figure 1.
In this schedule Manufacturing Phase II cannot proceed until receipt of a critical gear component. To highlight the importance of this gear’s delivery date on the start of Manufacturing Phase II we could insert a SNET constraint on the Manufacturing Phase II activity. This works well to show the importance of the delivery date, but it does not describe the complete schedule situation. If Manufacturing Phase II is delayed we want to know the reason for the delay: either a manufacturing slippage or a gear delivery slippage. To provide a more complete picture of schedule accountability we want to insert a milestone for gear delivery receipt.
Highlight the Manufacturing Phase II task and select the task tab | Insert ribbon group | Task drop down menu and task, Figure 2.
Make the task a Gear Delivery Receipt milestone with Quality Assurance Phase I the predecessor and Manufacturing Phase II the successor, Figure 3.
Now if Manufacturing Phase II slips we will know if it’s due to internal manufacturing delays or an external gear delivery delay, which is beyond the control of the manufacturing crew. So the milestone complements the constraint by displaying delivery slippage accountability.
Microsoft Project constraints work well to highlight the importance of a particular date on the start of a respective activity. But if this activity slips you will want to describe whether the task delay is due to an internal or external dependency. This description is achieved by inserting a delivery receipt milestone with the constraint date. This milestone and constraint combination helps to tell the full schedule story in the case of a slippage or, worse, a contract dispute.