This calculator determines the mandrel diameter needed to render a given spring diameter.
Equation:
\( D_m = kD - d \)
Where:
\( D_m \) is the diameter of the mandrel,
\( k \) is the diameter coefficient,
\( D \) is the final diameter of the spring, measured from the center of the wire (not the outer or the inner spring diameter),
\( d \) is the diameter of the wire.