Brep Workflow for Thread Fails in GHPython, Succeeds in Grasshopper?

Hi,

I’m back trying to construct a water-tight thread brep in GHPython from scratch and failing.

Some of you might remember this topic from about two years ago, where I encountered the same issue, while trying something similar, and never really managed to solve it.
I’m trying a different way of constructing the thread here, namely by lofting its defining helical curves.

This Grasshopper definition leads to a closed thread brep, which is fabulous.

However, when translated to GHPython using RhinoCommon a broken, open brep is the result.

import Rhino.Geometry as rg
import scriptcontext as sc


MTOL = sc.doc.ModelAbsoluteTolerance
ATOL = sc.doc.ModelAngleToleranceRadians

# Hardcoded Constants Matching Input Geometry (don't change)
PLANE = rg.Plane.WorldYZ
MAJOR_DIAMETER = 4.0  # M4
PITCH = 0.7           # M4
TURN_COUNT = 123

if __name__ == "__main__":
    # Create Thread
    thread_brep = rg.Brep.CreateFromLoft(C, rg.Point3d.Unset, rg.Point3d.Unset, rg.LoftType.Straight, False)[0]

    # Trim Thread to Length And Construct Caps
    start_plane = rg.Plane(PLANE.Origin + PLANE.ZAxis * (PITCH + MTOL), -PLANE.XAxis, PLANE.YAxis)
    end_plane = rg.Plane(PLANE.Origin + PLANE.ZAxis * (PITCH * TURN_COUNT - MTOL), PLANE.XAxis, PLANE.YAxis)
    
    cutter_domain = rg.Interval(-MAJOR_DIAMETER, MAJOR_DIAMETER)
    cutter_breps = []
    cap_breps = []
    for plane in [start_plane, end_plane]:
        # End cutters
        rect = rg.Rectangle3d(plane, cutter_domain, cutter_domain)
        corners = [rect.Corner(i) for i in range(4)]
        p, q, r, s = corners
        cutter_breps.append(rg.Brep.CreateFromCornerPoints(p, q, r, s, MTOL))
        # End caps
        rc, crvs, _ = rg.Intersect.Intersection.BrepPlane(thread_brep, plane, MTOL)
        boundary_breps = rg.Brep.CreatePlanarBreps(crvs, MTOL)
        cap_breps.append(boundary_breps[0])

    thread_brep_segments = thread_brep.Split(cutter_breps, MTOL)

    thread_brep = None 
    for brep_seg in thread_brep_segments:
        #brep_seg.Edges.RemoveNakedMicroEdges(MTOL)
        #brep_seg.Edges.MergeAllEdges(ATOL)
        bbox = brep_seg.GetBoundingBox(False)
        dist_start = start_plane.DistanceTo(bbox.Center)
        dist_end = end_plane.DistanceTo(bbox.Center)
        if(abs(dist_start - dist_end) < MTOL):
            thread_brep = brep_seg
            break

    #faces = [f.DuplicateFace(False) for f in thread_brep.Faces]
    #thread_brep = rg.Brep.JoinBreps(faces, MTOL)[0]
    
    start_cap, end_cap = cap_breps
    thread_brep.Join(start_cap, MTOL, False)
    thread_brep.Join(end_cap, MTOL, True)

    # Outputs
    B = thread_brep

Superficially, I do exactly the same, however I suspect the Grasshopper components to do some cleaning up and/or rebuilding here and there, basically some magic behind the scenes.

I’ve tried some de- and reconstructing the brep, but to no avail. Cleaning up naked micro edges and merging all edges also didn’t seem to do much.

Thanks for taking a look!

thread-rhf.gh (127.2 KB)

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