A DWG that is 60 MB for a simple floor plan is a common sight. Opening it is slow, and linking or importing it into Revit can slow the whole model down. The size almost never comes from the drawing itself: it comes from what has built up inside the file over years of editing and copying.

What makes a DWG heavy

  • Unused definitions. Layers, blocks, linetypes and text styles that are no longer used stay in the file until they are purged.
  • Nested blocks. Blocks inside blocks inside blocks are hard for other software to read and multiply the number of objects.
  • 3D noise. Objects at different elevations, or with a thickness, in a drawing that should be flat. Revit then has to place them in 3D space.
  • Duplicate geometry. Lines or arcs drawn twice on top of each other, often after a copy or a merge.
  • Stray objects. A single object far away from the drawing makes the extents huge, so the file looks tiny on screen when you zoom to fit.
  • Proxy objects. Objects created by other applications that the current program cannot interpret.
  • Dense hatches and splines with thousands of boundary points, and images embedded or referenced many times.

A cleaning routine

  1. Keep the original. Always work on a copy.
  2. Audit. Run the AUDIT command in your CAD program to repair errors in the drawing.
  3. Explode blocks that are not needed as blocks, keeping text attributes you need.
  4. Flatten. Move everything to a single elevation, Z = 0, for a 2D plan or detail.
  5. Purge unused layers, blocks, linetypes and styles.
  6. Remove duplicates and invalid objects (the OVERKILL command does this in AutoCAD).
  7. Check the extents for stray objects and the position of the drawing relative to the origin.
  8. Save to an older or more compatible format if the receiving software needs it.

Doing it in your browser

CAD Cleaner runs this routine on a DWG or DXF in your browser. The drawing is not uploaded: the cleaning engine runs on your computer and the files are removed when you leave the page. It audits the drawing and repairs errors, explodes nested blocks, flattens everything to Z = 0, purges unused layers, blocks, linetypes and styles, removes zero-length, invalid and empty objects, removes exact duplicate lines and arcs, and reports stray objects far from the drawing. You can choose the drawing type (general, architectural, structural or MEP), whether to keep elevations, and whether to centre the drawing at the origin. It can save a DWG, which is the smallest, or a DXF for maximum compatibility.

After cleaning, the compare view shows the original and the cleaned drawing side by side or overlaid, so you can check that nothing important was lost before you use the file.

Link, do not import

In Revit, linking a CAD file is generally better than importing it. An import copies the CAD geometry into the model, where it adds weight, while a link keeps it outside. In either case a clean drawing means fewer objects for Revit to process, and a drawing with a sensible origin lines up with the model.

What to check afterwards

  • Open the cleaned drawing and compare key dimensions with the original.
  • Check that the layers you need are still there and are named as expected.
  • Check the units, since an unexpected unit setting changes the size of imported content.
  • If the drawing is a survey or must keep real elevations, do not flatten it. Choose to keep elevations instead.

Cleaning changes a file. Keep the original, keep a note of what was changed, and agree with the drawing’s owner before you issue the cleaned copy.