Sean Kim

Guide to using OpenCAD · Sean Kim

DWG, DXF, STEP, STP and SKP: differences and CAD viewer selection

First decide whether you need to check dimensions, review a 3D model or send production data to a factory. The file extension and your task help identify the right viewer and any additional information to request.

Cover of the OpenCAD drawing, 3D model and toolpath tools.
OpenCAD tools: viewers and instructions for each file type.

Compare file formats and what to check

What you check in OpenCAD depends on the file type. Files with the same extension can hold different data depending on the application and version that saved them, so check those too.

CAD file selection: drawings, 3D models and toolpaths
File formatWhat to checkAdditional information
DWG · DXF2D drawing dimensions, layers, text and layoutsSave version, drawing units, external references and fonts
STEP · STP3D parts, assembly structure, sections and stored PMIExport options, units and missing parts
SketchUp SKPSketchUp models, tags, scenes and componentsSave version, hidden state and reference dimensions
NC · G-code · MPRTool motion, code lines and parsing warningsMachine/controller, units, origin and tool information

How do DWG and DXF, or STEP and STP, differ?

DWG and DXF are different drawing file formats. When exchanging drawings, match the receiving application's supported format and save version, then reopen the result to check text, dimensions and external references.

STEP and STP are extensions used for the same STEP format. Export settings can affect geometry, assembly structure, colors and PMI. Renaming STP to STEP does not restore missing information.

SKP is a SketchUp model file. A 3D display does not make it equivalent to STEP geometry, a production bill of materials or CNC machining code.

Open files on Windows or Mac without installation

Use OpenCAD on Windows or macOS in a current browser supporting JavaScript and WebGL2. Browser capabilities, device memory and file complexity matter more than the operating system alone. On mobile, start with viewing and dimension checks; use a computer for editing.

  1. Check the file extension and the application/version that saved it.
  2. Choose the DWG/DXF, STEP/STP, SKP or NC viewer from the OpenCAD tools.
  3. Learn the controls with a sample file before opening your own.
  4. Check fit-to-view, visibility and a known reference dimension. If anything looks wrong, follow the instructions for that format.

Viewing a file and converting it are different tasks

Changing a filename extension does not convert the format. If you need another format, export it from the source application and reopen the result in the receiving application.

Within its supported scope, OpenCAD's DWG/DXF CAD provides drawing editing, saving and PDF output. The STEP, SKP and NC viewers do not provide universal format conversion or CAM process generation. First establish whether you need a PDF/image, an editable drawing or 3D geometry.

Handoff checklist for design teams, furniture factories and machine shops

Send reference information together so the same part can be compared across files. When sending a revision, identify which drawings, parts lists and machining files changed to avoid mixing versions.

  • Common: record part/panel IDs, revision, date, units and reference dimensions.
  • Drawings: check the save version and external references, and prepare a PDF for comparison.
  • 3D models: compare part count, assembly placement and reference orientation with the original.
  • Furniture: align BOM/label IDs, material thickness, grain/edge directions and front/back conventions.
  • Machining: separately check the machine/controller, origin, tools and loading orientation against shop-floor requirements.

Open-source implementation and usage guide