Subtractive Wedge¶

In one sentence: Cut a tapered box-shaped cavity — a wedge whose top face is smaller than or offset from its bottom face — out of an existing Part Design Body solid.

Overview¶

Workbench: Part Design · Menu: Part Design → Subtractive Primitives → Subtractive Wedge
Toolbar: Part Design Modeling Primitives · Shortcut: none

Subtractive Wedge removes a wedge-shaped volume from the current tip of the active Body using a Boolean cut. The wedge is an OCCT generalised tapered box defined by ten coordinates: minimum and maximum extents along X, Y, and Z at the base level, plus independent minimum and maximum extents for a second rectangular face at the top. This lets you cut tapered pockets, angled slots, prismatic ramps, and asymmetric channels that would require complex sketch work to produce any other way.

Intuition¶

A wedge is best understood as a box whose top face has been independently resized and repositioned relative to its bottom face. The bottom face sits in the XZ plane and is defined by the intervals [Xmin, Xmax] and [Zmin, Zmax]. The top face, at height Ymax, is independently defined by [X2min, X2max] and [Z2min, Z2max]. FreeCAD connects the four corners of the bottom face to the four corners of the top face with straight edges, producing a solid with six quadrilateral faces.

Concretely: - Set all four *2* values equal to the corresponding base values for a plain rectangular box with no taper. - Shrink the top face relative to the bottom face (e.g. X2min > Xmin and X2max < Xmax) to get a classic "roof ridge" wedge that comes to a ridge at the top. - Shift the top face sideways (e.g. X2min = X2max = some_value) to get a parallelogram cross-section — useful for angled entry chamfers or ramp pockets. - Set both top extents to the same value on one axis to get a true sharp edge at the top (a proper wedge-shaped taper).

All ten coordinates are independent distances, not widths, so the shape is fully described by absolute min/max pairs rather than a centre + size.

When to use it¶

You need a tapered pocket or chamfered entry — for example, a dovetail relief or an angled counterbore entry — where the top opening is a different size from the bottom.
You need to cut a ramp or inclined slot where one end is taller than the other.
You want an asymmetric tapered cavity that would require a complex lofted pocket to create otherwise.
You are roughing out a complex shape quickly and want to subtract approximate wedge volumes before refining with sketch-based operations.

When NOT to use it¶

The cavity is a simple rectangular box — use Subtractive Box instead; its Length/Width/Height parameters are easier to reason about for untapered slots.
You need to add a wedge-shaped boss — use Additive Wedge, which has identical parameters but fuses material.
The taper is on a cylindrical surface — use Subtractive Cone for conical bores.
No solid exists in the Body — subtractive primitives require an existing base feature. FreeCAD will display an error if the Tip is empty.

Step-by-step walkthrough¶

Prerequisites: An active Part Design Body with at least one existing solid feature (the Tip must be non-empty).

Ensure the Body you want to modify is active. If it is not, double-click it in the model tree.
Activate Part Design → Subtractive Primitives → Subtractive Wedge from the menu, or click its icon in the Part Design Modeling Primitives toolbar. If multiple primitives share one toolbar button, expand the drop-down and select Subtractive Wedge.
The task panel opens with the ten wedge coordinate parameters. A preview of the default wedge shape appears in the viewport.
Set the base face coordinates. The base face sits at Y = Ymin (default 0): adjust Xmin, Xmax, Zmin, and Zmax to define the base rectangle.
Set Ymax to the height of the wedge (the Y extent of the cavity).
Set the top face coordinates. The top face sits at Y = Ymax: adjust X2min, X2max, Z2min, and Z2max to define the top rectangle. To produce a taper, make these values different from the corresponding base values.
Click OK. FreeCAD performs the Boolean cut and the Body shape is updated. The feature appears in the model tree as Wedge.

Tip

To visualise the shape before committing, sketch the desired cross-section on paper first. Label the bottom-face corners with the Xmin/Xmax, Zmin/Zmax values and the top-face corners with X2min/X2max, Z2min/Z2max. Then enter those values directly — the correspondence is one-to-one.

Ymin must be less than Ymax

FreeCAD requires Ymax - Ymin > 0 for the wedge to have a positive height. The default places Ymin = 0 and Ymax = 10. If you change Ymin, ensure Ymax remains strictly greater than Ymin.

Parameters¶

Parameter	Type	Default	Description
Xmin	Distance (mm)	0.0	Minimum X coordinate of the base face (at Y = Ymin).
Ymin	Distance (mm)	0.0	Y coordinate of the base face. Typically 0.
Zmin	Distance (mm)	0.0	Minimum Z coordinate of the base face (at Y = Ymin).
X2min	Distance (mm)	2.0	Minimum X coordinate of the top face (at Y = Ymax).
Z2min	Distance (mm)	2.0	Minimum Z coordinate of the top face (at Y = Ymax).
Xmax	Distance (mm)	10.0	Maximum X coordinate of the base face. `Xmax - Xmin` is the base face width. Must be > Xmin.
Ymax	Distance (mm)	10.0	Y coordinate of the top face. `Ymax - Ymin` is the wedge height. Must be > Ymin.
Zmax	Distance (mm)	10.0	Maximum Z coordinate of the base face. `Zmax - Zmin` is the base face depth. Must be > Zmin.
X2max	Distance (mm)	8.0	Maximum X coordinate of the top face.
Z2max	Distance (mm)	8.0	Maximum Z coordinate of the top face.

Constraints enforced by the source:

Xmax - Xmin must be > 0 (delta X cannot be zero or negative).
Ymax - Ymin must be > 0 (delta Y cannot be zero or negative).
Zmax - Zmin must be > 0 (delta Z cannot be zero or negative).
X2max - X2min must be ≥ 0 (delta X2 may be zero — top edge collapses to a line).
Z2max - Z2min must be ≥ 0 (delta Z2 may be zero — top edge collapses to a line).

Advanced usage¶

Ridge and sharp-edge wedges¶

Setting the top face to a line (e.g. X2min = X2max = 5.0) collapses one dimension of the top face to a single edge, creating a classic wedge that tapers to a ridge. Setting both X2min = X2max and Z2min = Z2max (to the same values) collapses the top to a single point, giving a pyramid-shaped cavity.

Parallelogram (shear) wedges¶

Setting X2min = Xmin + offset and X2max = Xmax + offset (the same offset for both) shifts the top face horizontally without changing its size. The result is a parallelogram cross-section — useful for cutting angled ramp slots where the cavity walls are slanted but parallel.

Dovetail approximation¶

A rough dovetail slot can be approximated by setting the top face wider than the base face (X2min < Xmin and X2max > Xmax). This inverted taper undercuts the base solid. For a true dovetail profile with a specific angle, use a Pocket with a constrained trapezoidal sketch instead.

Subtractive primitives vs. Pocket¶

Subtractive Wedge is most useful when the exact cavity dimensions are known as absolute coordinates (min/max pairs) and when the shape is one of the degenerate forms described above. For any cavity that must be positioned relative to existing edges, constrained to a bolt pattern, or defined by angles and dimensions rather than absolute coordinates, a Pocket with a sketch is more precise and easier to dimension correctly.

Common mistakes and pitfalls¶

Cannot subtract primitive feature without base feature

Cause: The Body's Tip is empty — no additive feature has been added yet.
Fix: Add at least one additive feature (Pad, Additive Box, etc.) to the Body before applying any subtractive primitive.

delta x/y/z of wedge too small — execution error

Cause: One or more of the base face extents is zero or negative (Xmax ≤ Xmin, Ymax ≤ Ymin, or Zmax ≤ Zmin).
Fix: Verify that each *max value is strictly greater than the corresponding *min value. The defaults (0 → 10) are safe starting points.

delta x2 or z2 of wedge is negative — execution error

Cause: X2max < X2min or Z2max < Z2min. The top-face size can be zero (collapsing to a ridge) but cannot be negative.
Fix: Ensure X2max ≥ X2min and Z2max ≥ Z2min.

Wedge cavity does not appear at the expected location

Cause: All coordinates are measured in the Body's local coordinate system. If the Body origin is not where expected, the wedge appears in the wrong place.
Fix: Use the Attachment tool to reposition the wedge's local coordinate system, or adjust the ten coordinate values to account for the offset from the Body origin.

Inverted taper causes Boolean failure

Cause: When the top face is much larger than the base face in both dimensions, the wedge walls flare outward and may extend outside the base solid, leaving material uncut or causing unexpected geometry.
Fix: Ensure the entire wedge volume is contained within the base solid, or switch to a Pocket with a lofted sketch for more control over an inverted taper.

Python API¶

Minimal example¶

import FreeCAD as App
import PartDesign

doc = App.newDocument()

body = doc.addObject("PartDesign::Body", "Body")

# Create a base block to cut into
box = doc.addObject("PartDesign::AdditiveBox", "Box")
body.addObject(box)
box.Length = 20.0
box.Width = 15.0
box.Height = 20.0
doc.recompute()

# Cut a tapered wedge slot from the top
wedge = doc.addObject("PartDesign::SubtractiveWedge", "Wedge")
body.addObject(wedge)

# Defaults: Xmin=0, Ymin=0, Zmin=0, X2min=2, Z2min=2,
#           Xmax=10, Ymax=10, Zmax=10, X2max=8, Z2max=8
doc.recompute()

print(f"Volume: {wedge.Shape.Volume:.4f} mm³")
# TODO: verify computed volume

Customising the wedge — a ridge-top taper¶

# Cavity with a full-width base and a ridge at the top (Z-ridge)
wedge.Xmin  = 0.0
wedge.Ymin  = 0.0
wedge.Zmin  = 0.0
wedge.Xmax  = 10.0
wedge.Ymax  = 8.0    # height of the cavity
wedge.Zmax  = 10.0
wedge.X2min = 0.0    # top face same width as base
wedge.X2max = 10.0
wedge.Z2min = 5.0    # top face collapses to a ridge at Z=5
wedge.Z2max = 5.0
doc.recompute()

Resulting feature properties¶

Property	Type	Description
`Xmin`	`App::PropertyDistance`	Minimum X of the base face, mm.
`Ymin`	`App::PropertyDistance`	Y coordinate of the base face, mm.
`Zmin`	`App::PropertyDistance`	Minimum Z of the base face, mm.
`X2min`	`App::PropertyDistance`	Minimum X of the top face, mm.
`Z2min`	`App::PropertyDistance`	Minimum Z of the top face, mm.
`Xmax`	`App::PropertyDistance`	Maximum X of the base face, mm.
`Ymax`	`App::PropertyDistance`	Y coordinate of the top face (wedge height), mm.
`Zmax`	`App::PropertyDistance`	Maximum Z of the base face, mm.
`X2max`	`App::PropertyDistance`	Maximum X of the top face, mm.
`Z2max`	`App::PropertyDistance`	Maximum Z of the top face, mm.