My_Heart_Threads

// response to openscad screw threads with linear_extrude by speedymollusc
// For OpenScad coders.

// A slice through a bolt has the shape of a shallow heart.
// If we look at it radially from zero to 180 degrees,
// it increases linearly from the minor to the major radius.
// At zero degrees it will have the radius of the minor radius of the threads
// at 90 degrees it will be at the pitch radius
// then at 180 degrees it will be at the major radius.
// It's the same on the other side of the heart just mirrored across the X axis.

// This shape is made in module MaleThread using a polygon
// with a point on the X axis at radius [MinorTR+j/180*TH,0]]
// this simple equation just progresses from the minor radius
// to the major radius as j (the angle) goes from 0 to 180
// Then this polygon is rotated j degrees to the proper position on the heart.
// This is hulled and then mirrored to the create the other half of the heart.

// three e