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CougarMtn 
Newbie
Joined: 28.Dec.2012
Location: United States
Using: AutoCad2000
Status: Offline
Points: 4
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 Topic: How to change arc length directly
Posted: 28.Dec.2012 at 21:28 |
I have an arc drawn on a chord (horizontal line with the arc fixed to either end).
I want to be able to directly change the arc length to some value. I can't. Using Properties I can change the radius, end angles, etc. but the arc length is grayed out and can't be altered. Changing the radius or arc center can alter the arc length , as can simply using grips to move the center point of the arc, but it is trial and error to get a specific value for arc length (301.3948 for example).
I could do it mathematically but that is tedious.
Is there anyway to directly input the value wanted for the arc length?
Thanks in advance.
Edited by CougarMtn - 28.Dec.2012 at 21:39
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amit.simplex
Newbie
Joined: 10.Feb.2012
Location: India
Using: Autocad civil 3D 2008
Status: Offline
Points: 4
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Posted: 29.Dec.2012 at 05:51 |
to change arc length you can use LENGTHEN command & provide total length of an arc or line. 
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heinsite
Senior Member
Joined: 05.Feb.2009
Location: United States
Using: AutoCAD 2014
Status: Offline
Points: 640
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Posted: 29.Dec.2012 at 05:59 |
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If you need to hold the chord length I don't think you have any choice other than working with the math. If it's something you need to do often build a spreadsheet to take the chord and arc lengths as inputs and solve for the radius. It's the one value you'll be able to modify in Properties.
Dave.
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Dave Hein, P.E.
Hawaii District Engineer
Kona International Airport
AutoCAD Certified Professional
Autodesk Expert Elite
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CougarMtn
Newbie
Joined: 28.Dec.2012
Location: United States
Using: AutoCad2000
Status: Offline
Points: 4
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Posted: 29.Dec.2012 at 06:12 |
Dave,
Thanks for the reply. The problem with changing the radius is that I can't keep the arc fixed to the chord. I think your solution is probably right but .......
Thanks,
G
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CougarMtn
Newbie
Joined: 28.Dec.2012
Location: United States
Using: AutoCad2000
Status: Offline
Points: 4
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Posted: 29.Dec.2012 at 06:22 |
Thanks. This sort of works. I can change the length of the arc but then I can't keep it fixed to the end of the chord. If I use grips to move it back to the end of the chord, the length changes back to the original. If I move one end back, the other end moves off of the chord.
Any suggestions?? Almost solved.
G
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heinsite
Senior Member
Joined: 05.Feb.2009
Location: United States
Using: AutoCAD 2014
Status: Offline
Points: 640
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Posted: 29.Dec.2012 at 06:23 |
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You're right. This is tricky. Setting up parametric constraints isn't working for me either, and if you don't somehow tie the location of the ends of the chord down changing the radius completely moves the arc!
Still looking. :)
Dave
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Dave Hein, P.E.
Hawaii District Engineer
Kona International Airport
AutoCAD Certified Professional
Autodesk Expert Elite
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CarlB
Senior Member
Joined: 16.Oct.2009
Location: United States
Status: Offline
Points: 321
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Posted: 12.Jan.2013 at 01:07 |
Cougar, I still don't follow what you want to change. If the chord length/location shouldn't be changed, nor the radius, then the arc you have can't be changed, as there is only one arc that has that radius & that chord. Maybe a picture would help.
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heinsite
Senior Member
Joined: 05.Feb.2009
Location: United States
Using: AutoCAD 2014
Status: Offline
Points: 640
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Posted: 12.Jan.2013 at 01:23 |
In order to be able to modify this from the Properties panel you're going to need to solve some simultaneous equations. With a fixed CHord length, changing the Arc length also changes the Radius. You'll see this if you do the drag modify technique. While the arc is changing so is the location (and length) of the Radius. How critical is that exact arc dimension really? If it's an absolute requirement you're going to have to dive into the math I'm afraid. And no, I haven't done it for you already. Sorry.  Dave
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Dave Hein, P.E.
Hawaii District Engineer
Kona International Airport
AutoCAD Certified Professional
Autodesk Expert Elite
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CougarMtn
Newbie
Joined: 28.Dec.2012
Location: United States
Using: AutoCad2000
Status: Offline
Points: 4
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Posted: 12.Jan.2013 at 02:14 |
Thanks Heinsite. I can do the math but was looking for a more direct method in ACad.
In reply to CarlB....I need to keep the chord length fixed. If I change the arc length......Yes, the radius will change but I need the ends of the arc to remain fixed to the ends of the chord. If I use LENGTHEN or change the radius, the arc length no longer fits on the ends of the chord.
Thanks for all your comments. I think Heinsite is right. There is no direct way in ACad and it has to be done mathematically.
Give this no further thought. Thanks all.
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