Sweep and twist

[Dov Grobgeld]

Hello,

I'd like to sweep a profile over a wire, while parameterizing the x-dir along the wire.

As an example, sweeping a thin rectangle over a circular path yields a torus with a rectangular cross section.

But I'd like to twist the rectangle's x-direction during the sweep.

Currently it seems like you have to choose between either sweep() in which you have no control (except by setting the isFrenet option) of the changing of the xdir.

Or twistExtrude() in which case the sweep is linear, i.e. an extrusion.

I'd like to combine them. Is this even supported by OpenCascade?

I suppose that I can linearize the sweep path and do tiny lofts between subsequent rotated profiles, but this seems very inefficient.

Any ideas?

Regards,

[Adam Urbanczyk]

cq.Workplane.sweep has auxSpine argument that allows you to achieve what want.

[Dov Grobgeld]

Thanks Adam.

How exactly is the auxSpine wire turned into the binormal direction? My guess was that the path and the auxSpine are parameterized by t between 0 and 1 and the binormal is the vector between auxSpine(t)-path(t). But the following example shows that this is not the case. In the example my path is a circle, and my auxSpine is a larger circle in the same plane. I assumed this would mean that the binormal would be in the radial direction over the circle, and the sweep would be unaffected and essentially a torus with a rectangular cross section. However this is what I got:

Here is my example:

#!/usr/bin/env python

import cadquery as cq
from cadquery import exporters

def sweep_wire(wire,
               profile,
               binormal=None,
               up = cq.Vector(0,0,1),
               isFrenet=True):
  '''Sweep the (plane) profile along the open or closed wire'''
  first_edge = next(iter(wire))
  plane_normal = first_edge.tangentAt(0)
  plane_point = first_edge.positionAt(0)

  x_dir = plane_normal.cross(up)
  plane = cq.Plane(origin=plane_point,
                   xDir = x_dir,
                   normal = plane_normal)

  auxSpine = cq.Workplane(plane).eachpoint(binormal) if binormal is not None else None
  return (cq.Workplane(plane)
          .eachpoint(profile) 
          .sweep(wire, isFrenet=isFrenet, auxSpine=auxSpine)
  )

aux = cq.Wire.makeCircle(11,(0,0,0),(0,0,1))
path = cq.Wire.makeCircle(10,(0,0,0),(0,0,1))
w,h = (1,2)
profile = cq.Wire.makePolygon([(0,0),
                               (w,0),
                               (w,h),
                               (0,h)]).close()

res = sweep_wire(path,profile,binormal=aux)

exporters.export(res, 'sweep-aux-spine.stl')   

Once I understand how this works, I'll create a PR with an example.

Thanks!

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[Adam Urbanczyk]

You did something weird (not sure what yet) with eachpoint. Try using add instead:

import cadquery as cq
from cadquery import exporters

def sweep_wire(wire,
               profile,
               binormal=None,
               up = cq.Vector(0,0,1),

               isFrenet=False):

  '''Sweep the (plane) profile along the open or closed wire'''
  first_edge = next(iter(wire))
  plane_normal = first_edge.tangentAt(0)
  plane_point = first_edge.positionAt(0)

  x_dir = plane_normal.cross(up)
  plane = cq.Plane(origin=plane_point,
                   xDir = x_dir,
                   normal = plane_normal)

  auxSpine = cq.Workplane(plane).add(binormal)
  return (cq.Workplane(plane)
          .eachpoint(profile)
          .sweep(wire, auxSpine=auxSpine)
  )

aux = cq.Wire.makeCircle(12,(0,0,0),(0,0,1))
path = cq.Wire.makeCircle(11,(0,0,0),(0,0,1))

w,h = (1,2)
profile = cq.Wire.makePolygon([(0,0),
                               (w,0),
                               (w,h),
                               (0,h)]).close()

res = sweep_wire(path,profile,binormal=aux)

[Dov Grobgeld]

Thanks Adam. Interesting find! Indeed using add() gets rid of the strange warping. However, it still doesn't seem to work as intended.

I tried a couple of different auxSpines to try to rotate the cross section, but the result was a no-op, as if I hadn't given the auxSpine parameter:

Tried turning the cross section 90 degrees by making the aux spine offset in the +Z direction:

aux = cq.Wire.makeCircle(10,(0,0,1),(0,0,1))

Tried turning the cross section 45 degrees by offsetting the spine in the radial and the +Z direction:

aux = cq.Wire.makeCircle(11,(0,0,1),(0,0,1))

So using eachpoint() does something weird (currently unexplainable), while add() causes auxSpine not to affect the sweep at all.

Any ideas?

Btw, I think it would be nice if in sweep(), auxSpine could be of type Wire instead of assuming it is a Workplane.

Regards,

Dov

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[Adam Urbanczyk]

You might have misunderstood how aux spine works. To get a twisted square torus you'll need an aux spine that coils around the main spine.