Pick the arc's first endpoint. This point is also the arc's start point.
Pick the arc's second end point, or type an angle.
Tilted
Draws an arc whose plane is tilted from the current construction plane.
Length
Sets the arc length as measured along the arc. Type a positive or negative number, or pick two points to specify the arc curve's length.
Tilted steps
Pick the arc's center, and choose the Tilted option.
Pick the start point for the arc.
Drag the mouse to start a three-point rectangle that defines the orientation of the tilt.
In a different viewport from the start point, using reference geometry, or with elevator mode, drag the rectangle to the angle of the tilt.
Pick the arc's endpoint, or type an angle, or choose the Length option.
Midpoint
Draws an arc from its midpoint.
Midpoint steps
Pick the arc's center, and choose the Midpoint option.
Pick a point for the midpoint and radius of the arc.
Pick the end point of the arc.
Or, type the total angle of the arc.
Or, choose the Length option and type the total length of the arc.
Deformable
The Deformable option draws a NURBS approximation of the arc with a specified degree and number of control points.
Default degree-2 arc with three control points (1).
Deformable degree-3 arc with ten control points (2).
Degree
Specifies the degree of the arc. When drawing a high-degree arc, the output curve will not be the degree you request unless there is at least one more control point than the degree.
Pick the arc's end point or type an angle, or choose the Length option (type L).
Tangent
Draws an arc tangent to selected curves with options to pick a point not on the selected curves or to specify a radius. Each prompt allows you to pick a point that is not on a curve for the arc to pass through. At some prompts, the option to enter a radius appears. The red arc in the image is tangent to both blue lines.
Select a second curve to make the arc tangent to. The tangent indicators adjust to fit the arc tangent to the two curves.
Select a third curve to make the arc tangent to. The tangent indicators adjust again to fit the arc tangent to the two curves. Or Press Enter to draw the reference circle from the first two points.
Drag the cursor around the arc, and click to choose from the suggested possibilities.
Point
The Point option appears for each prompt. It releases the command from the tangent constraint for that pick.
To use the point option
At any prompt, choose the Point option, and pick any point for the arc to pass through. The tangent indicators adjust again to fit the arc tangent to the two curves.
Example
In this example, the Point option is used to establish the first point on the arc.
Choose the Point option, and pick any point.
Select the second tangent curve or radius.
Select the third tangent curve.
Drag the cursor around the arc, and click to choose from the suggested possibilities.
Example
In this example the Point option is used to establish the second point on the arc.
Select the first tangent curve.
Choose the Point option again, and pick any point.
Select the third tangent curve.
Drag the cursor around the arc, and click to choose from the suggested possibilities.
FromFirstPoint
Forces the arc to go through the first picked point on the curve instead of allowing the point to slide along the curve.
Example
In this example the FromFirstPoint option is used to establish the start point on the curve.
Select the First tangent curve. The tangent cursor slides along the curve.
Choose the FromFirstPoint option, and pick a location on the curve.
Select the third tangent curve prompt, select a curve.
Drag the cursor around the arc, and click to choose from the suggested possibilities.
Radius
Specifies a radius. If a tangent point exists on the second curve that meets the radius requirement, the tangent constraint will appear at that point as you drag the circle.
Example
In this example the Radius option is used to establish the size of the arc.
Select the first tangent curve prompt, select a curve. The tangent cursor slides along the curve.
Select the second tangent curve.
Choose the Radius option and type a radius value.
Drag the cursor around the arc, and click to choose from the suggested possibilities.
Extension
Extends a curve with an arc to a specified end point.
The arc extension is not joined to the original curve.
To draw an arc extension and join it in one step, use the Extend command.
The center point is constrained to a plane perpendicular to the curve end. If the extension is drawn in a view perpendicular to the constraint plane, the input will be automatically locked parallel to the construction plane.
In other views Rhino tries to make sure one of the ortho directions is parallel to the construction plane. Press Shift when making the pick to maintain the ortho direction.