partcad 0.1.0

Framework for packaging CAD models

PartCAD

PartCAD is the first package manager for CAD models, and a Python package to consume these packages in CAD scripts (cadquery and build123d). It brings the same power to CAD scripting as pip to Python, npm to JavaScript, maven to Java etc.

PartCAD allows to maintain information about mechanical parts, how they come together to form larger assemblies, and to reuse the same parts in multiple assemblies, multiple projects. The implementation of parts can change over time (e.g. optimize or migrate to CadQuery from STEP) without the need to update all of the consumers.

• Installation
• Usage
  • Create new package
  • Add a dependency
  • Create a basic assembly
  • Render your project
• Modelling
  • Parts
  • Assemblies
  • Scenes
  • Packages
• Export
  • Visualization
  • Other modelling formats
  • Purchasing / Bill of materials
• Tools for mechanical engineering
• History

Installation

The recommended method to install PartCAD for most users is:

pip install partcad

For contributors:

git clone https://github.com/openvmp/partcad.git
cd partcad
python3 -m pip install -e .

Usage

Create new package

Initialize new PartCAD package in the current directory (create the default partcad.yaml):

pc init

Add a dependency

Use the following command to import parts from another package:

pc add <alias> <url-or-local-path>

Create a basic assembly

Here is an example that uses PartCAD to create a sample assembly.

# partcad.yaml
import:
  partcad-index:
    type: git
    url: https://github.com/openvmp/partcad-index.git
assemblies:
  assembly_01:  # declare an assembly object

# assembly_01.py
import partcad as pc

assy = pc.Assembly()  # create an empty assembly
pc.finalize(assy)     # this is the object produced by this PartCAD script

Render your project

Use the following shell command to render PartCAD parts and assemblies in the current package (the current directory):

pc render

If you are using VS Code then you can simply run your PartCAD script while having OCP CAD Viewer view open.

Modelling

This frameworks allows to create large models and scenes, one part at a time, while having parts and assemblies often maintained by third parties.

Parts

PartCAD allows to define parts using any of the following methods:

Method	Example	Result
STEP file	parts:   bolt:     type: step
Original CadQuery Gateway Interface	parts:   cube:

Other methods to define parts are in coming soon (e.g. build123d).

Assemblies

Assemblies are defined as parametrized instructions how to put parts and other assemblies together.

import partcad as pc

if __name__ != "__cqgi__":
    from cq_server.ui import ui, show_object

bolt = pc.get_part("example_part_step", "bolt")
bone = pc.get_part("example_part_cadquery_logo", "bone")
head_half = pc.get_part("example_part_cadquery_logo", "head_half")

model = pc.Assembly()
model.add(bone, loc=pc.Location((0, 0, 0), (0, 0, 1), 0))
model.add(bone, loc=pc.Location((0, 0, -2.5), (0, 0, 1), -90))
model.add(head_half, pc.Location((0, 0, 27.5), (0, 0, 1), 0))
model.add(head_half, pc.Location((0, 0, 25), (0, 0, 1), -90))
model.add(bolt, loc=pc.Location((0, 0, 7.5), (0, 0, 1), 0))
pc.finalize(model, show_object)

Assembly parameters can be of two kinds: build time and run time.

Assembly instances with different build time parameters are different assemblies, different models.

Assembly instances with different run time parameters are the same assembly, just visualized in a different state (e.g. different motion state).

Scenes

Scenes are defined as parametrized instructions how to place assemblies relative to each other for visualization purposes.

Scenes are intended to be used for visualization, simulation, validation and testing purposes. Scenes are not intended to be used outside of the package where they are defined.

Packages

Each PartCAD project is a separate package. Each package may export parts, assemblies and scenes. Each package may import parts, assemblies and scenes from its dependencies (other PartCAD packages).

Method	Example
Local files (present in your own source code repository)	import:   other_directory     type: local     path: ../../other
External GIT repository (HTTPS, SSH)	import:   other_directory     type: git     url: https://github.com/openvmp/partcad
External tar ball (HTTPS)	import:   other_directory     type: tar     url: https://github.com/openv...090ca.tar.gz

The full syntax is below:

import:
    <package-name>:
        desc: <(optional) textual description>
        type: <git|tar|local>
        path: <(local only) relative-path>
        url: <(git|tar only) url-of-the-package>
        relPath: <(git|tar only) relative-path-within-the-repository>
        web: <(optional) package or maintainer's url>
        poc: <(optional) maintainer's email>

Export

Visualization

Individual parts, assemblies and scenes can be rendered and exported into the following formats:

• PNG
• STL

Other modelling formats

Additionally, assemblies and scenes can be exported into the following formats:

• SDF (not yet / in progress)
• FreeCAD project (not yet / in progress)

Purchasing / Bill of materials

The bill of materials for each assembly can be produced using the following formats:

• CSV
• Markdown

Tools for mechanical engineering

Here is an overview of the open source tools to maintain mechanical projects. It shows where does this framework fit in the modern mechanical development workflows.

flowchart TB

subgraph repo["Your project's GIT repository"]
  subgraph custom_repo["Custom parts"]
    direction TB
    custom_part_internet["A STEP file\ndownloaded from Internet\nor the vendor site"]
    custom_part_cad["A part exported as a solid\nfrom a CAD tool not\nsuitable for collaboration"]
    custom_part_cq["An individual reusable part\nmaintained as a script\nunder a version control system"]
    custom_part_os["Another reusable part\nmaintained as a script\nunder a version control system"]
  end

  model["Your project's model\ndefined as Python code\nfor version control\nand collaboration"]

  subgraph scenes["Scenes"]
    test1["Capability 1\ntest scene"]
    test2["Capability 2\ntest scene"]
  end
end

subgraph external_repos["Third-party GIT repositories,\nCDN-hosted files or OCCI servers"]
  subgraph external_repo["Repository of standard\nor popular parts"]
  end
end

subgraph external_tools["External tools"]
  freecad["FreeCAD"]
  cadquery["CadQuery"]
  openscad["OpenSCAD"]
  gazebo["Gazebo"]

  partcad["PartCAD library"]
  style partcad fill:#c00
end

custom_part_cad <--- |Individual\ncontributor|freecad
custom_part_cq <--- |Part design\nworkflow| cadquery
custom_part_os <--- |Part design\nworkflow| openscad

external_repo ---> |Import| model
custom_repo ---> |Import| model
model -.-> |Import| test1
model -.-> |Import| test2

custom_repo <-. Maintained\nusing\nPartCAD\nconvention .- partcad
external_repo <-. Maintained\nusing\nPartCAD\nconvention .- partcad
model <--- partcad
test1 <--- partcad
test2 <--- partcad

test1 -.-> |Export| gazebo
test2 -.-> |Export| gazebo

History

PartCAD is the evolution of the modelling framework that was once used internally in OpenVMP. It is now being maintained separately as a generic tool.

The motivation behind this framework is to build a packaging and dependency tracking layer on top of CadQuery and traditional CAD tools to enable version control and other features required for effective collaboration.

This framework currently uses CadQuery and, thus, OpenCASCADE under the hood. However this may change in the future if the python C bindings for OpenCASCADE remain a blocker for unlocking multithreaded performance.