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How to make the classic PM Iron Triangle

Agile Tetrahedron Model
I was in a workshop just the other day and asked if everyone was aware of the dynamics of the classic project management iron triangle.  While most people had heard of it, it was apparent that few actually understood the dynamics of the model.
For a better model than the PM triangle see the Agile Tetrahedron.
Perhaps a physical model of the PM triangle would help people to grasp the meaning.  So let's build an adjustable Iron Triangle out of something.  It needs to be inexpensive, made from common items, and build-able in 20 minutes.

Here's is how to make a PM iron triangle out of plastic drinking straws.

You need:

  • Straws - the bendable kind - multi-colored.
  • Scissors
I used 3 yellow straws for the flexible corner pieces.  Cutting the straw just about 2cm beyond the flex on each side.  I cut the straw at an angle.  This makes assemble easier, as you must crimp and slide this piece into other straws.  The taper makes this easier.

Cutting diagram & finished triangle
Working on the red side.  I use 2 red straws.  Cut one into 3 pieces, throwing away the flex part.  The other is cut just to the side of the flex and throwing away the flex part also.  You are left with 3 red pieces, one short and two long.  Slide the yellow flex parts into the short red piece and the other yellow flex into one of the long red pieces.

One side of the adjustable triangle.
Repeat for the green side and the orange side.

All the pieces of the triangle
With the remaining long pieces we make the inner tubes.  Crimp the straw longitudinally so that it will become smaller and slide into the other straws.  Insert one end into the short red straw.  Do the same for the green and orange sides.
The 3 angles
 Now the angles may be assembled into a triangle.  Sliding one straw over the crimped straw.  This allows the sides to adjust in length.  And flex at the corners.

You now have an adjustable Project Manage Iron Triangle.  Label the sides and start playing with it.  Enjoy your new found understanding of the constraints of projects.

If you need an explanation of the power of the Iron Triangle and its limitations as a model for software development listen to the Agile in 3 Minutes: episode 21 Predict.


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