AutoCAD arc length

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.

Start, Centre, Length

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:

Command:  LENGTHEN
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.

 

Find out more about using AutoCAD on one of our AutoCAD training courses in London: Click here for more information.

 

Comments

U save my life... thanks for tutorial! :)

Sweet! I have been doing this for a while and ran into a constant lap problem for hooped rebar (represented via a polyline). This is so much better than calculating arc length via angle and diameter and using that for the extra length. I abhor putting text in place of the actual measurement, so now I can follow proper practice easily! Now... to figure out how to make a block for these hoops... Thanks!

Thank you for posting.

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