Sketch
A drawing on a plane with dimensions and constraints: the source of extrusions, revolves and cuts in 3D. Tools, arcs, construction lines, dimensions, constraints and the tracing underlay in detail.
How a sketch works
A sketch lives on a plane (XY, XZ, YZ or a face of a body). It is more than lines: every object has points, and you can add constraints between them (“this line is horizontal”, “these two are equal”) and dimensions (“length 150 mm”). A solver recomputes the drawing after each change, so the part stays as intended when you later edit a single dimension.
The status at the top shows “DOF: N” (how much freedom is left), “Fully defined” (nothing can move) or “Conflict” (constraints disagree). Closed profiles are counted next to it: the body is built from them. Blue lines can still move, dark ones are fully defined.
Units (mm, cm, m) are switched in the header; grid step and snapping (G) are in the palette on the right. The sketch is saved with the project, and the Timeline at the bottom has one mark per step (line, dimension, constraint). Click a mark to preview the sketch at that moment, double-click to edit the step.
Tools
- Select (V)
- select and drag points, lines, dimensions. A box dragged left to right takes only what is fully inside, right to left takes everything it touches. Arrow keys move the selection by the grid step.
- Line (L)
- as a chain: each click continues the line. Enter, Esc or a double-click ends the chain.
- Rectangle (R)
- two corners; sides get horizontal and vertical constraints automatically.
- Circle (C)
- centre, then radius.
- Arc (A)
- centre, start, end. The arc runs counter-clockwise from start to end.
- Three-point arc (K)
- start, end and a point on the arc.
- Tangent arc (U)
- continues the last line or arc smoothly, with no kink.
- Slot (S)
- an elongated hole with rounded ends.
- Polygon (Y)
- regular: centre, then a point sets radius and rotation.
- Fillet (F)
- click two crossing segments: the corner is replaced by an arc tangent to both; type the radius or change it later with a dimension.
- Trim (T)
- click a piece between intersections and it disappears (red shows what will be removed).
- Offset (O)
- a copy of a contour at a given distance on the chosen side.
- Mirror (M)
- select objects, press Next, then pick the symmetry axis: any line or an axis through the origin.
- Pattern (N)
- copies around a centre or on a grid: count, step or angle.
- Project edge (P)
- brings an edge of an existing body onto the sketch plane as a construction line.
- Dimension (D)
- see “Dimensions”.
Typing numbers while drawing
While drawing, just type a number: for a line it is the length, then the angle; for a rectangle the width and height; for a circle the radius. Enter confirms, Tab moves to the next field. The part comes out exact without extra dimensions.
Arcs
An arc is defined by centre, start and end and always runs counter-clockwise from start to end. So with “centre, start, end” the order of your clicks matters: if the arc came out on the wrong side, the order was reversed.
To bulge an existing arc the other way, select it and press “Flip arc” in the Constraints block. The arc is mirrored about its chord: the endpoints stay where they are while the centre moves to the other side. Dimensions and constraints are kept; if they do not allow the flip, the action is undone and the conflicting constraint is highlighted in red.
Radius and the distance between the endpoints are set with dimensions (D): click the arc for the radius, click its two endpoints for the distance. To join an arc smoothly to a line, select both and press Tangent.
Construction lines
Construction geometry is for layout: symmetry axes, a circle the holes sit on, a diagonal, a guide at an angle. It is drawn as an orange dashed line and is not part of the profile, so it never interferes with an extrusion or a cut.
There are two ways to make one. First: press the Construction button at the end of the left toolbar (key X) and draw as usual: everything new is construction. Second: select objects you have already drawn and press X (or the button): they become construction. Press again to turn them back into normal geometry. The button stays highlighted while the mode is on.
What you can do with a construction line
- Points
- attach a point to the line with Coincident (select the point and the line) or Midpoint: the point slides along the line. The end of another line can be placed on it the same way.
- Dimensions
- a construction line is measured like any other: length, angle to another line, distance from a point or from the origin.
- Constraints
- horizontal, vertical, parallel, perpendicular, equal, symmetry about it: all work as with normal lines.
- A typical trick
- draw a vertical construction axis, build half of the part and mirror it with the Mirror tool, or constrain points symmetric about this axis.
- Profile
- construction lines never end up in closed regions and never split them.
Dimensions
The Dimension tool (D) picks the type from what you select: a line gives a length, a circle or arc a diameter or radius, two points a distance, two lines an angle. For a distance along one axis hold Shift (horizontal) or Alt (vertical). Then type the value, with units if you like, for example 12 mm or 1.5 cm.
A dimension has a handle: drag it to change the value with the mouse, or drag the label to move it. Double-click a dimension to type a number. Adding a second identical dimension to something already measured opens the existing one instead: you never get two equal dimensions.
If a dimension contradicts other constraints the change is undone and the conflicting constraints and dimensions are highlighted in red. Remove the extra one and try again.
Constraints
| Horizontal, Vertical | One or several lines |
|---|---|
| Parallel, Perpendicular | Two lines |
| Equal | Two lines or two circles/arcs: same length or radius |
| Tangent | A line and a circle/arc, or two circles |
| Coincident | Two points (merged into one) or a point and a line/circle (the point lies on it) |
| Midpoint | A point and a line: the point halves the line |
| Symmetry | Two points and an axis line |
| Flip arc | With an arc selected: flips it |
| Fix | Points or objects: cannot be moved or resized until unfixed |
| Angle | Two lines: adds an angle dimension |
Tracing underlay
To trace an existing sketch, drawing or photo, insert an image: the “Insert image…” button in the palette, drag a file onto the sketch, or Ctrl+V from the clipboard. PNG, JPG, WebP and SVG work; for a PDF take a screenshot of the page. The underlay sits beneath the drawing, is not part of the profile and does not get in the way of selection.
Set the scale from a known size: mark two ends of a segment on the image and type its real length. Turn on “Move and resize” to drag the image; the blue square in the corner resizes it. Opacity and visibility are set in the palette, and Remove underlay removes it. Then trace with lines, arcs and circles and add dimensions over the underlay.
Tips
- Shape first, dimensions after
- draw a rough outline, add horizontal and vertical constraints, then dimensions: the solver stays happy.
- Aim for “Fully defined”
- then nothing moves by accident. Fix whatever is left if you need to.
- No profile
- check that line ends meet (Coincident) and that the lines you need are not construction.
- Delete and Ctrl+Z
- delete and undo; the wheel zooms, Space or the right button pans.