Cutting and etching

This example demonstrates the qtcad.builder.Builder.cut and qtcad.builder.Builder.etch operations, as well as how to save and restore the z-coordinate.

Initialization

from qtcad.builder import Builder, Polygon, Mask

Initializing the Builder

Below, we initialize a new instance of qtcad.builer.Builder and define a couple of simple shapes we are going to use in the following.

footprint = Polygon.box(10, 10, name="base").centered()
circle = Polygon.regular(10, 1.8, name="circ").centered()
thin = Polygon.box(10, 0.4, name="thin").centered()

box_mask = Mask("footprint")
box_mask.add_shape(footprint)
box_mask.add_shape(circle)
box_mask.add_shape(thin)

builder = Builder().add_mask(box_mask)
builder.print_mask_tree()

Layout
└── Mask 0 "footprint"
    ├── 0  Polygon  "base"
    ├── 1  Polygon  "circ"
    └── 2  Polygon  "thin"

<qtcad.builder.builder.Builder object at 0x7fe14b3ba490>

Base geometry

Next, select the generate a geometry with an uneven surface. We use qtcad.builder.Builder.set_group_name to tell the Builder to assign all subsequently created entities to the physical group "model_base". We also use qtcad.builder.Builder.copy_shape to create two translated versions of the circle shape. Using qtcad.builder.Builder.save_z and qtcad.builder.Builder.set_z we can save and restore the z-coordinate of the top of the "base" volume.

builder = (
    builder.set_group_name("model_base")
    .set_mesh_size(10)
    .use_mask("footprint")
    .use_shape("base")
    .extrude(2)
    .save_z("box_top")
    .use_shape("circ")
    .copy_shape(translate=(0, 2))
    .extrude(1)
    .set_z("box_top")
    .copy_shape(translate=(0, -4))
    .extrude(1)
)

As promised, all volumes share the same physical group:

builder.view(
    surfaces=False,
    volume_labels=True,
    angles=(-45, 0, 45),
    save="figs/cut_base.svg",
    font_size=15,
    zoom=0.8,
)

<qtcad.builder.builder.Builder object at 0x7fe14b3ba490>

Cutting

Builder.cut(depth: float, noclip: bool = False) → Self

[🏗️ Operation] Cut the currently selected shape(s) into the model up from the current z coordinate down by depth length units. If noclip=True, the cutting is performed on the whole model rather than clipped by the selected shapes.

See also etch which follows the contours of the top surface.

Parameters:

depth – The distance by which to etch the selected shapes down into the model.
noclip – Whether to cut the shape without horizontally clipping to the current shapes.

Next we will make a cut of depth 1 through the first tube shape.

builder.group_from_shape().use_shape("thin").copy_shape(
    name="cut", translate=(0, 2)
).cut(1)

<qtcad.builder.builder.Builder object at 0x7fe14b3ba490>

The cut operation effectively extrudes the currently selected shape(s) downwards and then removes the intersection with existing geometry.

builder.view(
    surfaces=True,
    volume_labels=True,
    surface_labels=False,
    angles=(-45, 0, 45),
    save="figs/cut_result.svg",
    font_size=15,
    zoom=0.8,
)

<qtcad.builder.builder.Builder object at 0x7fe14b3ba490>

The created surfaces are labeled base on the current naming mode (see Selection of shapes and naming modes).

builder.view(
    surfaces=False,
    volume_labels=False,
    surface_labels=True,
    angles=(-45, 0, 45),
    save="figs/cut_surfs.svg",
    font_size=15,
    zoom=0.8,
    groups=["cut_bottom", "cut_side"],
)

<qtcad.builder.builder.Builder object at 0x7fe14b3ba490>

Etching

Builder.etch(depth: float, noclip: bool = False) → Self

[🏗️ Operation] Etch the currently selected shape(s) into the model up from the current z coordinate down by depth length units. This is done by cutting into each top surface. If noclip is True, then the surface is not clipped to the currently selected shapes.