---
title: Bisect
order: 4
---

Bisect cuts a shape with a plane and throws away one side. It is the cheapest way to flatten a face, slice a shape in half, or trim a chain against a reference frame. No cutter object is required, and the cut edge can carry the same blend profiles the booleans use.

![a polyline Bisect modifier with its three fence planes expanded](../assets/modifiersettings-bisect.webp)

## Adding a bisect

- **Modifier panel**: *Add Modifier → Bisect*
- **Pie menu** (`Q`): the *Bisect* button in the South wedge's modifier grid, next to Mirror
- **Right-click menu**: *Modifiers → Bisect*
- **Active tool**: switch the Chisel tool to [Bisect mode](../interface/active-tool.md#bisect-mode) and drag a cutting line straight across the viewport

Selection decides how the plane is seeded:

- **One shape selected**: you get a *Custom* plane at the object's own origin along its local Z. Edit *Location* and *Normal* in the panel, or slide the plane with its [gizmo](#gizmo).
- **Two or more selected**: the **active** object becomes the plane: every other selected shape is cut across the active object's origin and local Z axis. An Empty makes an ideal plane handle.

## Cut kinds

A bisect item is either a single **Plane** or a **Polyline** fence. The kind is set when the modifier is created (the panel header shows which): panel-added bisects are always Plane; the tool's Polyline gesture produces a Polyline.

### Plane

One infinite cutting plane, from one of two sources:

- **Object** *(default)*: another object's origin is a point on the plane and its local **+Z** is the normal. Leave *Plane Object* empty to use the modified object's own origin and Z. Moving the plane object updates the cut live.
- **Custom**: an explicit **Location** and **Normal**, expressed in the modified object's local space, so the plane travels with the object.

![Drawing a bisect line in the viewport](../assets/bisect-line.webp)

### Polyline

A fence of connected planes: one plane per drawn segment, with the first and last segments unbounded. Each plane after the first records how it joins the fold of the planes before it, and can fillet that join.

![Drawing a polyline bisect fence](../assets/bisect-polyline.webp)

In the panel each plane gets its own block, in draw order. Plane 1 shows only *Location* and *Normal*. It seeds the fold, so it has no fold or corner rows. Every plane after it adds:

- **Fold**: *Union* (cut where this plane **or** the previous planes cut) or *Intersect* (cut only where this plane **and** the previous planes cut). Set from the drawn corner's turn direction.
- **Location / Normal**: same as a Custom plane, editable per segment
- **Corner Blend**: fillet radius on the crease where this plane meets the previous one (`0.0` = hard corner)
- **Profile / Smooth**: Round / Sharp / Soft / Tight / Chamfer for that corner, plus the chamfer smooth

## Common parameters

- **Flip**: keep the other side of the cut. Available on both kinds.
- **Blend**: enable a smooth fillet along the cut edge, with the usual **Profile** and **Smooth** controls. `0` blend is a hard, exact planar cut.

## Gizmo

Every cutting plane of a Bisect draws a handle in the viewport while the object is active and selected: the single plane, a plane object's frame, and each plane of a polyline fence alike.

| Handle | Action |
|---|---|
| **Blue arrow** (one per plane, pointing at the side that gets cut away) | Drag to slide the plane along its normal. For an *Object* plane it moves the plane object itself |
| **Orange ring** (in the cutting plane, around the first arrow) | Drag to set the cut-edge **Blend**. Leaving zero switches Blend on, like the arc gizmo |
| **Orange corner dot** (one per polyline corner, floated out along the crease) | Drag to set that corner's **Corner Blend**. Its distance from the crease *is* the value, so dragging to zero and back up is direct |

![sliding a plane, blending the edge, rounding a corner](../assets/bisect-gizmo.webp)

Both blend drags take the standard rounding hotkeys: `1`–`5` pick the profile, `S` slides the chamfer smooth when the profile is Chamfer. `Space`, `Enter` or releasing the mouse confirms; `RMB` or `Esc` cancels and restores everything, the plane object's position included.

A plane that uses the *Object* source with no plane object set cuts across the modified object's own frame and draws no arrow. Moving it would mean moving the object itself.

The gizmo has its own **Bisect** section in *Render Properties → Gizmos*, with a master toggle and a separate switch for the blend handles. See [Render Engine: Gizmos](../render-engine/gizmos.md#bisect).

## From the pie menu

With a bisected object active, the pie's East wedge shows a row per Bisect: the flip toggle, the blend profile icons, the blend radius and chamfer smooth, and a label naming the plane: *Custom Plane*, the plane object's name, *(own origin)*, or *Polyline (3 planes)*. Plane locations and normals stay in the panel.

## Drawing a bisect in the viewport

With the Chisel tool in **Bisect** mode, LMB-drag draws the cut. Select the SDF objects you want to cut first. The gesture reports a warning if nothing eligible is selected. Every selected object gets its own bisect modifier whose plane passes through that object's own origin, projected onto the drawn plane.

| Key | Line | Polyline |
|---|---|---|
| **LMB-drag** | Draw the cutting line | Draw the first segment |
| **LMB-click** | — | Add a fence corner |
| **`Space` / `Enter`** | Confirm | Accept the fence |
| **`Backspace`** | — | Remove the last corner |
| **`F`** | Flip the kept side | Flip the kept side |
| **`Ctrl`** | Toggle angle snap | Toggle angle snap |
| **`Shift`** | Precision | Precision |
| **`RMB` / `Esc`** | Cancel | Cancel |

The shaded side of the preview is the side that gets cut away, and the default keeps the bulk of the selected objects. `F` swaps it if you want the other half.

## Notes

- `Ctrl + D` (Duplicate Chain) remaps the plane object along with the rest of the graph, so the copy cuts against its own plane, not the original's.
- A [Smooth](smooth.md) modifier rounds bisect cut edges like any other join, but leaves a polyline's per-corner radii alone.

## See also

- [Active Tool → Bisect mode](../interface/active-tool.md#bisect-mode): the viewport gesture
- [Interface: Gizmos](../interface/gizmos.md): every gizmo family and its colours
- [Boolean](boolean.md): cutting with a shape instead of a plane
- [Rounding & Blending](../rounding-and-blending/index.md): what the blend profiles look like