CAD Forum -- Specifying Arc Length

      There are several ways to specify an arc in AutoCAD, knowing just the length of the arc and the radius. September 24, 2006

I need to be able to draw an arc in ACAD2005 that is a specific length and radius. These will be the only two known variables. I can't use a chord measurement. We are jigging a known radius between points. I will be able to measure the jig's radius (measuring the chord will be too inaccurate). Can anyone give us any help with this?

Forum Responses
(CAD Forum)
From contributor A:
I come across this fairly often. The only way that I have come up with to tackle this problem is a little convoluted. I first draw an arc at the given radius but at some arbitrary length. I then use the Lengthen command and select T for Total. Then just select the arc and it will extend or shrink to the length you gave.

From contributor A:
I forgot a step. After you select T for Total, you will prompted to give a value. At that point you will type in the length you want the arc to be.

From the original questioner:
Thanks - that works.

From contributor B:
You can use some math to get angle:
angle= (length*180)/PI*R
now just draw arc with center, radius, angle

From contributor C:
1. In ought-to-CAD draw a circle of the desired radius and list the circumference.
2. Divide the desired radius by the circumference.
3. Multiply the result from #2 by 360 to obtain the circle section for the required arc.
4. Draw two lines of the calculated angle from the center of the circle to the circle.
5. There’s your arc of the desired length.

From contributor C:
2. Divide the desired length (not radius) by the circumference.

From contributor D:
It's simple - draw the circle first with the radius that you have, then select draw point and then "measure" command to the length that you have. The points are going to be spaced to that # in circle - and just break the rest of that and you have your arch.

From contributor E:
We are using '06 and do this on the pointer but on the command line don't you get the options - center, end?
select a start point
E for end - put in your fixed length
acad will now ask for (Angle, Direction, Radius) type R enter and type your radius enter.
You should see your arc.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Computerization

  • KnowledgeBase: Computerization: CAD Computer Related Design

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article