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Elliptical arc

Draw part of an ellipse from its centre, its long axis, its width and where it starts and ends, or trim an ellipse into one.

  • Elliptical arcSketch toolbar: under the ▾ next to Circle
What other CAD programs call it
SchoolCADOnshapeFusionSOLIDWORKS
Elliptical arcElliptical arcEllipse, then TrimPartial Ellipse

An elliptical arc is part of an ellipse: an oval curve that stops. Use it for the curved top of a sign, the rocker of a toy, an arched doorway or the rim of a scoop. It is under the ▾ next to Circle, just below Ellipse.

It has everything an ellipse has (a centre, a long axis and a width) plus a start and an end, which are points.

How to use it#

  1. In a sketch, choose Elliptical arc from the ▾ next to Circle.
  2. Click the centre.
  3. Click the end of the long axis. Nearly level or upright snaps level or upright (H or V).
  4. Move sideways and click to set the width. The whole ellipse shows dashed.
  5. Click where the arc starts, then move round the way you want it to go and click where it ends. The arc follows the way you moved, so it can go either way round.
  6. Use Dimension D on the arc for its major and minor radius, as for an ellipse.

Trim makes elliptical arcs too#

Draw a whole ellipse and the lines that cross it, then use Trim X and click the piece of the ellipse to take away. What is left is an elliptical arc that ends where the lines crossed, held there with point on line constraints. Trim an elliptical arc again to shorten it, or to cut a piece out of the middle: the two pieces share one centre and one set of axes, so they stay the same ellipse and its sizes still hold both.

Tips#

  • The start and end are points: snap lines to them, or join them with Coincident, to close a shape. Select a line that starts there and the arc, then click Tangent, for a smooth join with no corner. A half ellipse closed by a straight line makes a region that extrudes, revolves or cuts like any other.
  • Drag the arc to move it. Drag its start or end to slide it round the ellipse. Drag the end of an axis to turn or stretch the ellipse it is part of.
  • Mirror and the sketch patterns copy elliptical arcs. Extend stretches a line to meet an ellipse or an elliptical arc.
  • Offset on an elliptical arc makes a curve beside it with its own two ends: join the ends with two short lines for a curved strip, such as a handle or a rim.
  • Elliptical arcs come out true (exact) in STEP files when the exact geometry engine is on, and as a smooth outline in the laser cut file.

If it does not work#

  • The arc went the wrong way round. Undo and draw it again, moving round the other way before the last click.
  • The shape will not extrude. Check that the arc's start and end meet the other lines exactly: snap them onto the line ends, or add Coincident.