Drawing arc lengths

[Anonymous]

I am constructing a site plan and have the radius length and the arch length. How would I draw a specific arc length?

Thanks in advance
Happy Hoildays

[Anonymous]

One way to do it, once you have drawn the arc (oversized) you can use the distance tool (with divisions etc) and stretch your arc back to the correct length. Note that it measures from the closest end where you first hover over the arc.

[TomWaltz]

I never thought about that before..... Yuck!!

[Anonymous]

TomWaltz wrote:
I never thought about that before..... Yuck!!

How would you do it?

[Aussie John]

s2art wrote:
One way to do it, once you have drawn the arc (oversized) you can use the distance tool (with divisions etc) and stretch your arc back to the correct length. Note that it measures from the closest end where you first hover over the arc.

Good thinking Stuart
Messy way to do it but I am not sure this is an easier way.

[Erika Epstein]

What about geometry?
If the circumference of a circle is 2πr
arc a =arc length

then to get the angle θ defined by the radius and arc length both of which you know:
θ = (arc a)360°/ 2πr

[TomWaltz]

s2art wrote:

TomWaltz wrote:
I never thought about that before..... Yuck!!

How would you do it?

I meant that I never thought about drawing by arc length. It doesn't seem like there's a good way.

[Aussie John]

Erika wrote:
What about geometry?
If the circumference of a circle is 2?r
arc a =arc length

then to get the angle ? defined by the radius and arc length both of which you know:
? = (arc a)360°/ 2?r

Actually Stuarts way is very easy. I like the CAD method as I dont need to calculate things like you had to in the pen and ink days. They aint called computers for nothing

[Erika Epstein]

Not a problem; I prefer a more precise method.

[Anonymous]

Don't you all design with a Calculation at your side?....

I guess this is only for the Engineers. Erika, (as most times) is correct and brings us the most efficient way.

Delta = ( 180 * Arc length ) / (Pi * Radius)

This delta is the distance "a" to "drag" the arc. I usually just start the arc and leave the cursor at the beginning and then type"a", then type the angle (i.e. 45d23'15") and then the + (or negative depending on the direction), then enter.