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Draw a circular arc

Place the endpoints first and control the bow with a constrained centre.

About 5 minCadivari 0.3.0Watch and try

Useful first: Draw connected lines

Cadivari constructs an arc from a start point, an end point and a constrained centre. Both endpoints must remain equally far from the centre. The arc curves away from the centre and its sweep cannot exceed 180 degrees.
Cadivari constructs an arc from a start point, an end point and a constrained centre. Both endpoints must remain equally far from the centre. The arc curves away from the centre and its sweep cannot exceed 180 degrees.

Cadivari constructs an arc from a start point, an end point and a constrained centre. Both endpoints must remain equally far from the centre. The arc curves away from the centre and its sweep cannot exceed 180 degrees.

Try it in Cadivari

  1. Place the endpoints

    In a Top-plane sketch, press A or click Arc. Click the start point, then a different end point. These two clicks establish the chord, not the centre.

  2. Position the constrained centre

    Move perpendicular to the chord. The centre marker stays on its perpendicular bisector, and the dashed radius guides connect it to both endpoints. Moving farther away makes a shallower arc.

  3. Make a semicircle

    Hold Shift during centre placement to lock the sweep to exactly 180 degrees on the chosen side. Click a third time, press Enter or click the green check to commit the valid preview.

  4. Set an exact span

    Press V and select the arc. In Properties, set X1 to 0, Y1 to 0, X2 to 120 and Y2 to 0 mm, then set Sweep to 180. Its radius is now 60 mm.

  5. Compare a shallower arc

    Change Sweep to 90 in Properties. The endpoints stay fixed while the centre and radius update. Undo to restore the semicircle.

Over to you

A small exercise

Create a 120 mm wide semicircle with a 60 mm radius. Use Line to join its two endpoints, snapping to each green Endpoint marker, then finish the line with Enter.

What you should see

The arc and straight line form a D-shaped closed path. Selecting either segment reports Closed. The arc remains separately editable.

Things to look out for

  • The third point sets the constrained centre; it is not a third point on the curve.
  • A radius cannot be smaller than half the endpoint distance, and a sweep above 180 degrees is not supported.
Check your understandingWhy does the centre move along a fixed line

Every point on the perpendicular bisector is equally far from both endpoints. Constraining the centre there keeps the arc truly circular.

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Go deeper in the knowledge base

Instructions checked against the Cadivari 0.3.0 source and knowledge base on 2026-09-16. Lesson revision 1.