AutoCAD: How to construct an Arc of a Specific Length
Whilst teaching a recent AutoCAD course I was asked by a boat designer how to construct / draw an arc of a specific length. This set me thinking and trying out a number of possible options. The problem with the arc is that you can draw arcs in over nine ways but none of those specify a length of the arc.
You can define the chord length with Start, Center, Length, but in this case we want to define the arc length, not the chord.
It could of course be done by calculating the angle mathematically, but an easier way to do it is to draw the arc with the required radius and centre point, then modify it using the lengthen tool on the Modify tab drop down.
With the Lengthen tool you can set the object’s total length, including the Arc length:
Select an object or [DElta/Percent/Total/DYnamic]: T (Do NOT select the object enter T for Total)
Specify total length or [Angle] <1.0)>: 20 [enter]
Select an object to change or [Undo]: Now select the arc to lengthen
The arc will now be the desired length. If it is not in the correct location just rotate it around its centre point.
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