How to: Draw an Arc with a Specific Arc Length?

This question appears in our local forum. Is there any way we can create an arc by defining the arc length? There is no direct way to do this. There are some methods that seem to allow you define length. For example start, center, length. But this is defining the chord length, not the arch length.

chord_length

There is a suggestion to calculate the angle using simple mathematic calculation, comparing the arch radius and arch length. After you get the angle value, then you can draw it. But it is not easy.

One of our member, Ast, suggest a better solution: draw the arch, then modify it using lengthen tool.

AutoCAD_lenghten_tool

Lengthen tool allows you to define the object total length, including an arch. Select the total length option, then type the distance you want.

Command:  LENGTHEN
Select an object or [DElta/Percent/Total/DYnamic]: T

Specify total length or [Angle] <1.0000)>: 1000

Select an object to change or [Undo]:

Now if I try to inquiry or see the arc properties, I will see the arch has the exact length I wanted.

arch_length_properties

I never need to draw arch by defining it’s length. Any body knows why we would need to do that?

Comments

    Leave a Reply

    Your email address will not be published. Required fields are marked *

  1. Linda Williams says

    To all Professional Engineers and Professional Land Surveyors who are skeptical of their plan checkers.

    Why the length of a curve, if used in a land description, should be used only as a reference if at all.

    Amazon Books: Land Descriptions including lots of Samples.

  2. Fire flame says

    Having worked in Mechanical engineering field for a number of years I have run into a number instances where have worked with limited information when drawing a new part. When drawing arcs you may not have determined all the information you need. You may know the length but not know center. So rather than spending time searching for the unknown work with the drop down that matches the information you do have and move on.

  3. Erika says

    I have to do it all the time: when we work with documents that describes an area, they always describe using the lenght and 2 points. The command "Lenghten" don work properly for me, beacause besides the specific lenght, I also have 2 points that can't be changed. In other words, the radius, unknown, varies…..

  4. Erika says

    I have to do it all the time: when we work with documents that describes an area, they always describe using the lenght and 2 points. The command “Lenghten” don work properly for me, beacause besides the specific lenght, I also have 2 points that can’t be changed. In other words, the radius, unknown, varies…..

  5. joshua says

    man you have know idea how much this tip helps. up until now, the project i was working on was kicking my trash. THANKS!

  6. atiq says

    hello every body

    i want to know .. that

    why dimensions are spread here and there when we move an object ?

    plz solve my problem

    atiq

  7. Odong says

    Edwin, thanks for the info, greatly usefull! I'm laying a subsea cable and need to modify our route. I need to define an exact arch length as our new lay route for the cable end. This is the best answer.

    Greeting from all Surveyors :)

  8. Richard says

    We have to measure "girth" dimensions all the time on ships, so we lay out arc lenths on the screen for verification.

  9. says

    Who needs to draw an arc with a specific length? Surveyors need to do it all the time. Based on a legal description, something like, "Then an arc to the left, having a radius of X and length of Y". I was hoping dynamic input and grips would be an alternative but it looks like you have the best way to do it.

Trackbacks