Cutting spiral groove in a cylinder ?

I am trying to cut a spiral groove in a cylinder. Imagine a groove that starts at the top of the cylinder and spirals down for 90 degrees. The final drawing will be 4 such grooves but if I can get help on one I can copy and space the rest. I used a plugin from the engineers toolbag and got the best results so far but the look I am after would be similar to having the cylinder in a CNC mill and using an end mill to pierce the wall and cut down as the cylinder turns 90 degrees.
Any ideas?

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