Substracting a coil from a pipe

Hi,

I am building a barrel to wind a wire on to.
The helix i defined with the primitive geometry
The barrel wire is mounted on, i have swept a square work plane along a parametric equation, of the helix.
To make the barrel i just then defined two cylinders,
thought i could just use use a boolean operator to subtract the square cross section helix.

Please find attached,
Many thanks