by John Flanagan
You can use grips to quickly change the geometry of a basic shape in AutoCAD. In the example below a rectangle has been selected to show the grip controls (Fig 1). Hovering over the grips makes them active, they turn red and options appear enabling you to change the outline geometry. When you hover over the centre grips the Convert to Arc option becomes available.
Fig 1: Rectangle with Grips and Convert to Arc Option
When you select the Convert to Arc option in the example above make sure Ortho is toggled on in the status bar, drag your mouse down the screen and click. The result is illustrated in Fig 2 below.
Fig 2: Line Converted to Arc
The line on the right has been converted to a convex arc. To create a concave arc on the opposite side we need to mirror the Polyline about a central horizontal axis. See Fig 3 on the next page.
Fig 3: Polyline Mirrored about Horizontal Axis
Make sure you select Yes to erase source objects from the command prompt.
Create the Concave Arc following the same procedure as above. The final result is illustrated in Fig 4 below.
Fig 4: Convex and Concave Arcs using Central Grip Controls
Tip: As with a lot of exercises in AutoCAD there is usually more than one way to do it. Try the above exercise again but this time draw one rectangle from top left to bottom right and another rectangle from top right to bottom left. Convert the side lines in each rectangle to Arcs and compare the results. One rectangle will show Convex Arcs and the other rectangle will show Concave Arcs.