Back tool lathe mode not working

lathe_shapes = [
        None,                           # 0
        (1,-1), (1,1), (-1,1), (-1,-1), # 1..4
        (0,-1), (1,0), (0,1), (-1,0),   # 5..8
        (0,0)                           # 9
    ]
    lathe_shapes_back = [
        None,                           # 0
        (-1,-1), (-1,1), (1,1), (1,-1), # 1..4
        (0,-1), (-1,0), (0,1), (1,0),   # 5..8
        (0,0)                           # 9
    ]
    def lathetool(self, current_tool):
        glDepthFunc(GL_ALWAYS)
        diameter, frontangle, backangle, orientation = current_tool[-4:]
        w = 3/8.
        
        if '-X' in self.geometry:
            frontangle = 360 - frontangle
            backangle = 360 - backangle

        radius = self.to_internal_linear_unit(diameter) / 2.
        glColor3f(*self.colors['lathetool'])
        glBegin(GL_LINES)
        glVertex3f(-radius/2.0,0.0,0.0)
        glVertex3f(radius/2.0,0.0,0.0)
        glVertex3f(0.0,0.0,-radius/2.0)
        glVertex3f(0.0,0.0,radius/2.0)
        glEnd()

        glNormal3f(0,1,0)

        if orientation == 9:
            glBegin(GL_TRIANGLE_FAN)
            for i in range(37):
                t = i * math.pi / 18
                glVertex3f(radius * math.cos(t), 0.0, radius * math.sin(t))
            glEnd()
        else:
            if '-X' in self.geometry:
                dx, dy = self.lathe_shapes_back[orientation]
            else:
                dx, dy = self.lathe_shapes[orientation]

            min_angle = min(backangle, frontangle) * math.pi / 180
            max_angle = max(backangle, frontangle) * math.pi / 180

            sinmax = math.sin(max_angle)
            cosmax = math.cos(max_angle)
            tanmax = math.cos(max_angle)
            sinmin = math.sin(min_angle)
            cosmin = math.cos(min_angle)
            tanmin = math.cos(min_angle)

            circleminangle = - math.pi/2 + min_angle
            circlemaxangle = - 3*math.pi/2 + max_angle
            d0 = 0

            x1 = (w - d0)

            sz = max(w, 3*radius)

            glBegin(GL_TRIANGLE_FAN)
            glVertex3f(
                radius * dx + radius * math.sin(circleminangle) + sz * sinmin,
                0,
                radius * dy + radius * math.cos(circleminangle) + sz * cosmin)
            for i in range(37):
                #t = circleminangle + i * (circlemaxangle - circleminangle)/36.
                t = circleminangle + i * (circlemaxangle - circleminangle)/36.
                glVertex3f(radius*dx + radius * math.sin(t), 0.0, radius*dy + radius * math.cos(t))

            glVertex3f(
                radius * dx + radius * math.sin(circlemaxangle) + sz * sinmax,
                0,
                radius * dy + radius * math.cos(circlemaxangle) + sz * cosmax)

            glEnd()
        glDepthFunc(GL_LESS)