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Prepare CAD for upload

How you export your CAD decides how well Bramble can mesh it. Follow these steps before you upload Parts.

Export in millimetres

Bramble assumes all geometry is in millimetres. It doesn't scale files on upload, and it doesn't warn you if the units are wrong. A file exported in metres comes out 1000 times too small.

Export the surfaces

  1. Set the export units to millimetres.

  2. Export triangulated surfaces with:

    • a maximum edge length of 10 mm
    • a chord deviation of 0.2 mm

    The chord deviation is what captures radii and curved surfaces, so don't export coarser than this. 3. Export in a supported format: .stl, .stlb, .nas, .msh or .blend, optionally gzipped. See file formats and limits.

Split the model into Parts

  1. Export one file per Part. Each file becomes one Part. Several smaller files upload faster than one large one, and let you swap individual Parts between Runs.
  2. Plan the zone names. An .stl or .stlb file gets a single zone, the name you enter when you upload it. If you need several zones in an STL model, export each one as a separate file. .nas, .msh and .blend files keep the zone names stored in them. See zone naming.
  3. Name files deliberately. The file name becomes the Part name:
    • only letters, digits, ., - and _ are kept. Spaces and other characters are removed
    • a name that starts with a digit gets a _ in front
    • if the name is already used in the library, Bramble adds -1, -2 and so on

Clean up the geometry

  1. Make each surface watertight. Close any holes and gaps in each Part.
  2. Don't defeature. Keep the detail of the real geometry. An accurate result needs an accurate model.
  3. Leave overlaps in place. The mesher handles Parts that overlap or intersect each other, so you don't need to merge or trim surfaces where Parts meet.

Repair on Upload

For .stl files, tick Repair on Upload in the upload dialog to run an automatic surface repair. It joins nearly coincident edges, removes loose triangles, fills holes and makes the normals consistent. To use it, upload uncompressed files with a lower-case .stl extension. Repair doesn't guarantee a watertight Part, so still check the result after upload (below).

Check the Parts after upload

  1. On the Parts page, expand the library.
  2. Check each new Part's row:
    • Valid shows a tick if Bramble could read the surface.
    • Closed shows a tick if the surface has no open edges. A red warning icon, with the tooltip "This part contains open edges", means it has holes. The Part's Name is also shown in red.
  3. If a Part has open edges, fix the CAD and upload it again.

Bramble only checks for open edges. It doesn't report self-intersections or other surface defects.

If a Part doesn't appear

An upload row can show Complete even if Bramble couldn't process the file. In that case no Part is created and no error is shown. If a Part doesn't appear shortly after its row shows Complete, check that the file has at least one named zone and contains triangles. If it still doesn't appear, contact support@bramblecfd.com.

Related: Upload Parts · Zone naming · File formats and limits · Geometry