Cutting an OCCGeometry Spiral

MWE_occ_cut_spiral.py

#===============================
# Cutting a spiral (NOT WORKING)

import netgen.occ as occ
from netgen.webgui import Draw as GeoDraw
import numpy as np

tube_axes = occ.Axes(occ.Pnt(0,0,0), occ.Z)
tube_radius = 10
spiral_spacing = 2.1
spiral_width = 5
spiral_thickness = 0.8
revs = 3
angle = revs*2*np.pi
L = revs*(spiral_thickness + spiral_spacing) + spiral_thickness

cyl1 = occ.Cylinder(tube_axes, tube_radius, L).faces[0]
cyl2 = occ.Cylinder(tube_axes, tube_radius + spiral_width, L).faces[0]

seg1 = occ.Segment(occ.Pnt(0, 0), occ.Pnt(angle, L-spiral_thickness))
seg2 = occ.Segment(occ.Pnt(angle, L-spiral_thickness), occ.Pnt(angle, L))
seg3 = occ.Segment(occ.Pnt(angle, L), occ.Pnt(0, spiral_thickness))
seg4 = occ.Segment(occ.Pnt(0, spiral_thickness), occ.Pnt(0, 0))

arc1 = occ.Edge(seg1, cyl1)
arc2 = occ.Edge(seg2, cyl1)
arc3 = occ.Edge(seg3, cyl1)
arc4 = occ.Edge(seg4, cyl1)
arc5 = occ.Edge(seg1, cyl2)
arc6 = occ.Edge(seg2, cyl2)
arc7 = occ.Edge(seg3, cyl2)
arc8 = occ.Edge(seg4, cyl2)

wire1 = occ.Wire([arc1, arc2, arc3, arc4])
wire2 = occ.Wire([arc5, arc6, arc7, arc8])

spiral = occ.ThruSections([wire1, wire2])

cut = occ.Box(occ.Pnt(tube_radius + 0.5*spiral_width, 1, 0), occ.Pnt(tube_radius + 1.5*spiral_width, 2, L))
cut_spiral = spiral - cut

GeoDraw(cut_spiral) # Produces blank output screen.
GeoDraw(occ.Compound([cut, spiral])) # Confirms that cut and cut_spiral have a non-zero intersection.


#===============================
# Cutting a cylinder (working)

tube_axes = occ.Axes(occ.Pnt(0,0,0), occ.Z)
cyl1 = occ.Cylinder(tube_axes, 1, 1).faces[0]

seg1 = occ.Segment(occ.Pnt(0, 0), occ.Pnt(2*np.pi, 0))
seg2 = occ.Segment(occ.Pnt(0, 1), occ.Pnt(2*np.pi, 1))
arc1 = occ.Edge(seg1, cyl1)
arc2 = occ.Edge(seg2, cyl1)
wire1 = occ.Wire([arc1])
wire2 = occ.Wire([arc2])

cylinder = occ.ThruSections([wire1, wire2])

cut = occ.Box(occ.Pnt(0,0,0), occ.Pnt(2,2,2))
cut_cylinder = cylinder - cut

GeoDraw(cut_cylinder) # Visualizes 3/4 of a cylinder, as expected.