Measuring a section of a circle in AutoCAD / Draftsight?

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
I would like to measure the distance between two lines in a circle in Draftsight Really what I want to do is to place a tick mark on the edge of the circle as shown below, I want the tick mark to be right in the center of the two lines.


Draftsight has a Arc Length dimension feature but it is saying dimension is not a arc.
upload_2019-1-25_16-39-5.png
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Well I got it but it was really ugly. What I did was to temporarily split out that arc. I then copied it to another drawing and restored what I had. I then went to the temporary drawing and copied and pasted the arc to my main drawing and lined it up with the circle. I was then able to find the center.

Hopefully there is an easier way. ;)
 

shortbus

Joined Sep 30, 2009
8,479
Isn't what you want a "chord". Knowing the radius (or diameter) of the circle and the angle should give a chord. Or at least that's what it was called where I worked.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Isn't what you want a "chord". Knowing the radius (or diameter) of the circle and the angle should give a chord. Or at least that's what it was called where I worked.

You should know by now I am math handicap. The angle is 30 degrees. The radius of the circle is 1.8250". I do seem to remember from my geometry classes that I should be able to determine that distance but damns if I can remember. ;)
 

jpanhalt

Joined Jan 18, 2008
11,088
Just bisect the angle using equal-radius arcs, draw, and copy.

In my CAD program, it would be easy. As your radii intersect the perimeter, one click and the perimeter is segmented at those intersections. Then draw to the midpoint of each segment.

EDIT: Are you still trying to make one of these?
 
Last edited:

Alec_t

Joined Sep 17, 2013
12,009
Can you just draw one tick mark on the outer circle, then use the align/distribute tool to copy-and-rotate, with a 30° increment, to get the others?
 

eetech00

Joined Jun 8, 2013
2,321
Much of how AutoCAD acts on an object is the way the object was drawn. In other words, it won’t divide an arc if it thinks is a circle. Try dividing the circle into double the number of spokes.
 

shortbus

Joined Sep 30, 2009
8,479
You should know by now I am math handicap.
Believe me I suffer from the same malady.

Found this.

https://planetcalc.com/1421/

Works to get the length but I still needed a way to measure the midpoint in Draftsight.
When still working I always had to get out my "Machinery's Handbook" to find the formulas. Didn't have online access for such calculators. The other guys always made fun because I couldn't memorize the formulas.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Much of how AutoCAD acts on an object is the way the object was drawn. In other words, it won’t divide an arc if it thinks is a circle. Try dividing the circle into double the number of spokes.

What I ended up doing. But there HAS to be an easier way. These CAD programs already do such amazing stuff. Hard to believe it doesn't have that feature.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Can you just draw one tick mark on the outer circle, then use the align/distribute tool to copy-and-rotate, with a 30° increment, to get the others?
I will look it up to see if Draftsight has that. Or are you already refering to Draftsight?
 

MaxHeadRoom

Joined Jul 18, 2013
22,888
Also another way in Acad is to measure the angle of the adjacent radial lines and draw a line from centre to circ at the centre angle of the two and then place a point where the line intersects the circ.
Delete the line.
Max.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
I was thinking the freeware LibreCad, but assumed all reputable CAD software has a similar tool. As I mentioned in another thread, I uninstalled Draftsight when it started nagging for a fee.

I have not been nagged yet. I also use LiteCAD. Each product seems to do some things better. LiteCAD is superior at text IMHO.
 

MaxHeadRoom

Joined Jul 18, 2013
22,888
What I would probably do in Acad is to draw a 45° line from centre to circ, and place a point at the junction, then delete the line.
I keep my Coords command at = 2, I find this much more convenient and easier to do this kind of instruction.
Max.
 
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