Every manufacturing project has tasks, or steps, phases, or activities that define the work you'll perform. And some of those tasks are dependent upon others. In other words, you can’t start one step until another is completed. Or, there may be phases later in the process that won’t start until previous phases are finished.
Those are called task dependencies. Tasks are linked, and their dates depend on previous tasks.
In this video, we’ll look at four types of task dependencies that model actual conditions on the shop floor.
Let’s take a look!
Here on Standard Time® we’ll look at four distinct types of link relationships that you can see by the lines and the arrows in the Gantt chart. The first one we’ll look at is finish-to-start, which is the most common; then start-to-start, then finish-to-finish and finally we’ll take a look at start-to-finish.
Let’s go ahead and look at the most common link relationship which would be the finish-to-start. The starting date of a successor task is linked back to the finish date of another. When this task ends another can start. That’s the most common. We’ll move this task and you can see the next task updates because this one has been moved. Finish date on this one changed so that changes the starting date of the successor task.
The next type would be start-to-start. You can see the starting date of this task is linked back to the starting date of another. When that one is moved then the successor is also moved because the two start dates are linked together.
The third type would be finish-to-finish, where the finish date of this task is linked back to the finish date of another. We move that, the two finish dates are linked together and when the predecessor moves then the successor would also be updated.
The fourth type would be start-to-finish, where the starting date of this task goes down to the finish date of another. When we move this task then the successor also moves because the starting date is linked back to the finish date.
The examples you see down below are variations of we already looked at. We’ve got start-to-start; when the starting date of this task changes then the starting date of a successor task would change. We’ve also looked at the finish-to-finish; so when the finish date of this one changes then the finish date of the successor would also change. So you can combine these to form a nice little link relationship.
The long lines you see on these milestones are lag times. If we click on this link icon in the link column; we can go ahead and look at the lag times that you see connected with these link relationships. I should point out that the inbound tasks that you see here, actually none here, are predecessors and the outbound tasks are the successors. They are linked together with certain link relationships. In this case they have some lag times. I’ll click here, you can see the finish-to-start link relationship; which we already looked at. And a lag time of two calendar days. Close that and look at this one.
We have start-to-start, which we’ve also looked at previously with minus-four calendar days. Cancel out of these and that explains the long lines that you see here linked to these milestones. That covers the four distinct types of link relationships in Standard Time that you can use for your projects.