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  #1  
Old 06-28-2005, 02:11 PM
HERBERT HERBERT is offline
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Default CORD LENGTH TO A TRUE ARC LENGTH

YES I'M TRYING TO LAYOUT A CONE IN AUTOCAD AND WHEN I GO TO DRAW THE ARC FROM A TO B AND C TO D MY ARC IS ALWAYS LONGER. I FOUND OUT THAT THIS IS BECAUSE IT IS USING THE CORD LENGTH TO FIGURE THE ARC CAN ANY ONE TELL ME IF THERE IS A EQUATION TO TURN A CORD LENGTH INTO A TRUE ARC LENGTH.
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Old 06-28-2005, 10:07 PM
bordontn bordontn is offline
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Herbert.........Pi x chord length ?? = circumference of top or btm of cone..My CAD
won't lay it out either..If apex is at top; 1st chord is dia. of top of cone ,lower chord is dia. of btm of cone..Pi x each gives length of arc.. When I lay it out I use dividers
to step off the length of arc.
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Old 06-29-2005, 06:10 AM
HERBERT HERBERT is offline
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THANKS I'LL TRY THAT AMYBE I CAN GET AUTOCAD TO DIVIDE THE ARC. :?:
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Old 06-30-2005, 11:51 AM
tnbndr tnbndr is offline
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Herbert:
When using AutoCad or any drafting program you have to sometimes find workarounds to certain things. Instead of trying to draw the arc to length draw the entire circle using the diameter or radius. Then in AutoCad use the Draw/Measure command. It will prompt you to select the object (your circle) then the segment length. For the segment length enter the arc length that you want. Now you won't see anything until you set your Format/Point style to one of the crosshair type styles and do a regen.
Now you should see the circle segmented into several arc lengths. Just remember that AutoCad measures starting from 3 o'clock and goes counterclockwise (unless you have changed these settings under Format/Units/Direction). so don't use the arc from 3 o'clock clockwise as the last chord may not be of your specified length it will be whatever is left over.
Hope this explains it. If you have any other questions please post, I'll try to answer. I used to lay out round fittings in AutoCad in one of the Prehistoric shops I worked for and plot them full scale for patterns the shop to trace. Haven't done it in awhile but I remember finding ways to do the layout. Not as simple as everyone thinks. But once you figure it out it goes pretty quick.
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Old 07-16-2005, 05:03 PM
SteveB SteveB is offline
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S- Arc Length
R- Radius
Theta- angle being "subtended." This is the angle from start to finish.
S= R*theta.
Start there.
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