How to Subtract a Metaball in Blender

Subtracting a metaball from another in Blender is a quick way to create organic cutouts, holes, or negative space in your 3D models. By changing a metaball's active element property from positive to negative, it will carve into any overlapping metaballs within the same family group. This guide outlines the exact steps to achieve this effect efficiently.

Step-by-Step Guide to Metaball Subtraction

To subtract one metaball from another, follow these steps:

1. Create the Base Metaball

  1. Press Shift + A in the 3D Viewport.
  2. Go to Metaball and select a shape (such as Ball). This will act as your main positive geometry.

2. Add the Subtracting Metaball

  1. Select the first metaball and press Tab to enter Edit Mode (or remain in Object Mode if adding a new object).
  2. Press Shift + A > Metaball to add a second metaball shape, or duplicate the existing one using Shift + D.
  3. Move and scale the new metaball so that it overlaps the base metaball where you want the subtraction to occur.

3. Set the Element to Negative

  1. Select the metaball element you wish to use as a cutter.
  2. Go to the Object Data Properties tab (represented by a green metaball icon) in the Properties panel on the right side of the screen.
  3. Locate the Active Element section.
  4. Check the Negative box.

As soon as Negative is enabled, the selected metaball will subtract its volume from any intersecting positive metaballs.

Key Rules for Metaball Subtraction

  • Object Naming Families: Metaballs only interact if they belong to the same family. Blender groups metaballs based on the prefix of their object names (e.g., MBall, MBall.001, MBall.002).
  • Adjusting Influence: You can control the reach of the subtraction by tweaking the Stiffness setting under the Active Element section. Higher values make the cut sharper, while lower values create a smoother transition.
  • Converting to a Mesh: Once you achieve the desired shape, return to Object Mode, right-click the metaball, and select Convert To > Mesh to finalize the geometry for sculpting, editing, or exporting.