Sketching with constraints (sketch mode)

Sketch mode is a full constraint-driven sketcher, like the ones in SolidWorks, Fusion and Onshape. Geometry is held by constraints (horizontal, tangent, equal…) and dimensions (lengths, radii, angles — numbers or parameter formulas). The kernel solves the sketch every time the model rebuilds, so changing a parameter moves the sketch exactly as it would in your old CAD.

If you just want to doodle a profile, Sloppy sketch (S) is still there: draw roughly and it snaps clean. Its review card has a Constrain button (ruler and pencil icon) that opens the result in sketch mode with its constraints and sizes.

Enter sketch mode

• Tool rail → Sketch → Sketch with constraints, or ⌘K and type "sketch".
• Pick a flat face first to sketch on it, or choose Top (XY), Front (XZ) or Right (YZ).
• To change an existing sketch, hover its step in the Recipe and click the ruler-and-pencil icon (Edit sketch), or ⌘K → "Edit Sketch 2". Older shape-based sketches are converted on the way in, keeping their sizes and formulas.

The camera turns to look straight at the plane and switches to an orthographic view while you sketch (your projection comes back when you leave). Right-drag pans, the wheel zooms, Alt+drag orbits.

The sketch toolbar sits above the prompt bar and only exists while you sketch. The status chip at the top left says Fully defined, N DOF left or Over-defined.

Draw

While you draw, the cursor infers constraints and shows them as small glyphs: it snaps to end points and centers (they become the same point), midpoints, curves and their intersections, the origin and the axes, and to horizontal, vertical, tangent and perpendicular directions. Dotted guides show alignment with other points. Hold ⌘ / Ctrl to draw without inference.

X toggles construction geometry: with something selected it switches the selection, otherwise the next things you draw are construction lines (dashed). Construction geometry helps constrain but is never part of the profile.

Read the colours

A sketch does not have to be fully defined to build. Fully defined sketches are what make a model predictable when parameters change, so the status chip tells you how many degrees of freedom are left.

Constraints

Select geometry (click, ⇧-click to add, drag a box: left-to-right picks what is fully inside, right-to-left what it touches). The bar above the toolbar offers the constraints that fit the selection:

• One line: horizontal, vertical, fix.
• Two lines: parallel, perpendicular, equal, collinear.
• Point and line: coincident, midpoint. Point and circle: on the curve, concentric.
• Line and circle or arc: tangent. Two circles or arcs: tangent, equal, concentric.
• Two splines (or a spline and the curve it ends on): tangent, smooth (curvature continuous, G2).
• Two items and a line: symmetric about that line.

Constraint badges show next to the geometry (on small sketches always, on bigger ones when you point at or select the geometry). Click a badge to select the constraint; Delete removes it.

Fully define (the magic wand) adds what is missing — horizontal and vertical where lines are drawn that way, an anchor to the origin, sizes, then positions — using the current sizes.

Conflicts and redundancies

When a constraint or dimension cannot be true together with the others, it turns red and the bar says which ones it fights with, for example "Distance 50 mm: conflicts with distance 80 mm and vertical ×2". The sketch keeps solving without it. Fix it with Remove it, Make it a reference (a driven dimension that only measures), or ⌘Z.

A redundant constraint is already implied by others. It is shown red too, but the sketch still builds; you can keep or delete it. Constraints that the cursor inferred never end up redundant — they are dropped when something else already guarantees them.

Drag

With the select tool, drag points or curves. Everything that is still free follows; constraints always hold; fully defined geometry does not move. It is the quickest way to see what is still free.

Modify

Fillets and chamfers keep the sharp corner as a construction point, so dimensions to that corner keep working.

Finish

Enter (or Finish) saves the sketch as one Recipe step — one ⌘Z in the editor undoes it. A new closed sketch asks Extrude it? right away. Esc steps back: it cancels the current tool, then clears the selection; the ✕ button discards the sketch. Inside sketch mode ⌘Z and ⇧⌘Z undo and redo sketch changes.

While you edit an existing sketch, the model ahead of it updates live as a preview.

In the Recipe and the script

The Recipe sentence lists the sketch's key dimensions as chips ("Sketch a constrained profile (4 lines) on the XY plane — 80 mm, 40 mm"). Click a chip to change it; the kernel re-solves the sketch and everything after it rebuilds.

In script view a constrained sketch reads as constrained({ entities: [...], constraints: [...] }), one entity or constraint per line, with dimensions written as real formulas. Edit it there and it round-trips.

Ask the agent

While sketching, type or say commands in the prompt bar and sketch mode handles them right away, no credits used: "fully define this sketch", "add a dimension of 40" (on the selection), "make them parallel", "make it construction", "finish sketch".

Outside sketch mode the agent can build precise sketches for you:

Limits today

• Trim splits lines, arcs and circles; a spline is removed whole.
• Sketch on planes and flat faces; projecting model edges into a sketch (convert entities) is not available yet.
• Ellipses and text from older sketches can't be opened in sketch mode.

3D paths

For sweeps that leave a plane there are 3D paths: straight segments or a smooth spline through 3D points, and helices for springs, threads and coils. Ask the agent ("a compression spring, 20 mm diameter, 6 mm pitch, 40 mm long, 2 mm wire") or write one in script view:

const coil = path3d("coil", { kind: "helix", helix: { radius: 10, pitch: 6, height: 40, center: [0, 0, 0], axis: "Z" } });

Sweep a closed profile along it; the profile goes at the path's start, across the path (a helix around Z starts at the center plus the radius on X). Its radius, pitch and height are chips in the Recipe sentence. Drawing 3D paths with the mouse is not available yet.