newObject and cut() method

[bragostin]

I have created a newObject and want to perform a cut like this:

cut_new = cq.Workplane('YZ').box(L,W,H)
new = cq.Workplane('XY').newObject(list_of_shapes)
cut_new = new.cut(shape_to_cut)

but nothing happens: the new object remains unchanged. Is that to be expected?

[adam-urbanczyk]

I don't think this is correct. Could you share a minimum reproducible example?

[bragostin]

@adam-urbanczyk
This produces the intended result:

import cadquery as cq
box1 = cq.Workplane('XY').box(10, 20, 30)
box2 = cq.Workplane('YZ').box(10, 20, 30)
shape_to_cut = cq.Workplane('XY').box(15, 15, 15).translate((8,8,8))
new_object = box1.union(box2)
cut_object = new_object.cut(shape_to_cut)

while this does not:

import cadquery as cq
box1 = cq.Workplane('XY').box(10, 20, 30)
box2 = cq.Workplane('YZ').box(10, 20, 30)
shape_to_cut = cq.Workplane('XY').box(15, 15, 15).translate((8,8,8))
list_of_shapes = []
for o in box1.all(): list_of_shapes.extend(o.vals())
for o in box2.all(): list_of_shapes.extend(o.vals())
new_object = cq.Workplane('XY').newObject(list_of_shapes) 
cut_object = new_object.cut(shape_to_cut)

I would like to avoid using union because it is exceedingly slow with my real model.

[adam-urbanczyk]

Confirmed, it might be a kernel issue. I need to investigate.

[adam-urbanczyk]

I made some progress: it seems that OCCT bool ops do not like if the original shape has self intersections. In your example the two boxes d intersect. For now the workaround would be to perform the cut before constructing the compound.

I will still try if using this method allows to pefrom such an op in a single shot
https://www.opencascade.com/doc/occt-6.9.1/refman/html/class_b_rep_algo_a_p_i___builder_algo.html#a46ae85feda209da3074b8b77af6670a7

Note to self: some relevant methods/classes
TopoDS_Iterator -> iterate over subshapes of a compound
TopTools_ListOfShape

[bragostin]

@adam-urbanczyk then maybe a workaround could be to apply the the cut on each object of the list separately in a for loop?

[adam-urbanczyk]

Indeed, cut on separate objects and only then construct the compound.

[bragostin]

Indeed, the following code gives the expected result without unions:

import cadquery as cq

box1 = cq.Workplane('XY').box(10, 20, 30)
box2 = cq.Workplane('YZ').box(10, 20, 30)
shape_to_cut = cq.Workplane('XY').box(15, 15, 15).translate((8,8,8))
list_of_shapes = []
for o in box1.all(): list_of_shapes.extend(o.vals())
for o in box2.all(): list_of_shapes.extend(o.vals())
list_of_shapes = [ cq.Workplane('XY').newObject([o]).cut(shape_to_cut) for o in list_of_shapes ]
list_of_shapes = [ o.val() for o in list_of_shapes ]
cut_object = cq.Workplane('XY').newObject(list_of_shapes)