Bisect

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

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 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.
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

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

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

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.

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 modifier rounds bisect cut edges like any other join, but leaves a polyline’s per-corner radii alone.