1. George’s Bicycle
Creating a Gantt Chart

2. George is keen to build his own bicycle by using an old bike that he found in the garden shed. He believes that by salvaging the parts from this, and obtaining some parts from second-hand sources and others from the local bike shop, he can make a customised bicycle, at a far cheaper price than if he bought a new one.
He’s got all the parts, bar the back-wheel, the handle-bars and the rear gear-changing mechanism.
He needs to get the bicycle ready for a local race in 2 weeks time.

3. He’s worked out his work breakdown structure, and has estimated that each event will take this amount of time to complete: 
AA1 – take apart – ½ a day
AA2 – clean – 1 day
AA3 – painting – ½ day
AB1 – order – ½ day
AB2 – delivery – 7 days (The shop has to order the parts)
AC1 – re-assemble old parts – 1 day
AC2 – assemble new parts – ½ day
AD1 – 1st short test run – ½ day
AD2 – adjust & fine tune – ½ day
AD3 – final test run (race equiv.) – 1day

4. We need two things first:
A dependency list
A critical path analysis (sometimes an optional extra)
These two sound quite high-tec, but hopefully we can explain them quite clearly here.

5. Dependency List
Firstly, just list all the tasks, possibly from a Logic Diagram you’ve created. Also include the estimated time the task will take.
But some of these tasks cannot start until others before them have finished (called a finish-start relationship). So we need to note this. -
(Sometimes a task can start once another task has started – a start-start relationship. And what about a start-finish one?)

6. So here you can see that you can’t assemble the new parts until you’ve painted the frame (AA3) and the parts have been delivered (AB2)
Some tasks need more than one other task to finish before they can start -

7. Now – we have our dependency list from the work breakdown structure

8. What about the critical path?

9. We need some posh terms here again.
The most used approach to critical path analysis is the
PERT method (Programme Evaluation Review Technique).
This uses a “Node Box” as the base unit for storing
Information. Again, sounds high-tech, but hopefully we can
explain this.

10. The Node Box
The idea here is to contain information about a particular task in one clear diagram:
I’ve taken task AC1 (re-assemble old parts) as an example.
This centre-top box says how long
the task will take.
This centre box has the task code
or title.

11. diagram.This is where you’ll need a long piece of paper for a ½ decent
We need to have a box for each task, laid out in a structure like the logic
diagram.This is where you’ll need a long piece of paper for a ½ decent
sized project if you’re doing this manually!
And so on for all the tasks. To see the whole diagram – please go to the fileshare area – and open the spreadsheet titled “PERT Chart – Georges Bicycle”

12. The “Forward Pass”
We now need to start putting numbers in some of the other boxes.
The first ones are for the top row – earliest start time (EST) and earliest finish time (EFT). Doing this is called the forward pass, and essentially all it means is:
Transfer the EFT of the previous node box to the EST of the next box, add the duration to this, and put the total in the EFT box.
START has an EFT of 0:
= 0.5
Continue along the whole path – but watch out when you have two boxes going into 1:

13. 8 is higher than 3 – so 8 goes to next EST box.
watch out when you have two boxes going into 1 – choose the highest EFT from the two previous boxes (because that’s the earliest you can start the next task!).
8 is higher than 3 – so 8 goes to next EST box.
To see the whole diagram – please go to the fileshare area –
and open the spreadsheet titled “PERT Chart – Georges Bicycle”

14. The “Backward Pass”
Once you’ve gone along the whole chart, you will have a number in the EST box of the FINISH Task. Transfer this to the Latest Start Time (LST) box of the FINISH task:
And we now work back from this box along the whole chart
(Bear with me – we’re nearly there now!)

15. The “Backward Pass”
When working back – transfer the lowest Latest Start Time (LST) of the leading tasks to the Latest Finish Time (LFT) of the preceding task:
10 – 1 = 9
Take away the duration and put the answer in the bottom left (Latest Start Time (LST) box. Eg for AD3, 10 minus 1 = 9!

16. Remember – when two boxes go into one – choose the LOWEST figure to transer back in the backward pass:
The lower of 7 and 7.5 is 7!
To see the whole diagram – please go to the fileshare area –
and open the spreadsheet titled “PERT Chart – Georges Bicycle”

17. And enter that figure in the centre bottom box. 7 – 2 = 5 8 – 3 = 5
All that’s left to do is to calculate the difference between:
upper left hand corner & lower left hand corner
lower right hand corner & upper right hand corner
for each box.
(These two figures should always be the same!)
And enter that figure in the centre bottom box.
7 – 2 = 5
8 – 3 = 5
7.5 – 7.5 = 0
8 – 8 = 0

18. Task AC1 has a float of 5 days.
And where this figure is zero – this is your critical path!! (In technical terms – this means the “float” is zero) – You’ve no time to be flexible with these tasks!
Task AC1 has a float of 5 days.
Tasks AC2 and AD1 are on the critical path.
Now - to see the whole diagram in a manual format – please go to the fileshare area – and open the spreadsheet titled “PERT Chart – Georges Bicycle”. The complete analysis is the 5th sheet.

19. SO WE NOW HAVE OUR CRITICAL PATH

20. Next – create a table of tasks against time

21. Next – put in bars to represent the times for the task – and maybe link up the dependent ones with lines / arrows. Put the bars in the days that you can start them -

22. Now, tidy up the order to avoid crossing, add a legend, and add milestones!

23. YOU COULD HIGHLIGHT THE CRITICAL PATH IN RED –

24. Then you could start adding resources at the bottom:

25. And that’s it!