Other Ways of Drawing Circles in AutoCAD – 3P/2P/Ttr (tan tan radius)

This is a continuation of the previous tutorial I started in this post >> AutoCAD for Dummies: How to Draw a Circle. In that post I explained the very simple way to draw the circle on AutoCAD. This time there are other ways to draw it using the 3P (Draws a circle based on three points on the circumference.), 2P (Draws a circle based on two points on the circumference.), TTR (tangent tangent radius – draws a circle based on the tangent of the two objects either lines or arcs and you should specify the radius of the circle).

Drawing the 3P circle

First go the menu Draw>Circle>3 Points. Then the command prompt will say: _3p Specify first point on circle. This is simply telling you to pick a point on the screen which is your first point ( See Fig. 1 below. I’ved drawn the cross hair to illustrate the points). Then AutoCAD will ask you again, Specify second point on circle: Again it is asking you to pick another point to draw your circle. Pick another point as shown below in the illustration. Then you will see a circle a that looks like a rubber band that stretches whenever you drag your mouse.  You can can also see the command prompt asking you again to do something. It is telling you to specify the third point as shown below. Pick a point on the screen and drag your mouse to suit which size you like to create your circle. 

 

    autocad polyline icon

Fig. 1 Drawing a Circle Using 3 Points

 

Drawing the 2P circle

This method is simpler than the first one because it only requires you to pick two points on the screen to make the circle. It only needs the two endpoints of a diameter of the circle. So when you draw a circle using 2P, the two points are always an imaginary diameter even though you can’t see a line. There are two ways to draw it, by selecting the menu or typing it in the command prompt. You can also type the “C” or “Circle” command in the command prompt on the 3P or TTR. Again go to the menu Draw>Circle>2 Points then Autocad will prompt: Specify first end point of circle’s diameter: pick a point on the screen then it will prompt you again: Specify second end point of circle’s diameter: pick another point to create the circle (see Fig. 2 Below).

 

 

    autocad polyline icon

Fig. 2 Drawing a Circle Using 2 Points

 

Drawing the Tangent Tangent Radius circle

This command is particularly useful when making circle tangent to arcs, lines or circles. For example, if there is a line and an arc and you want to make a circle  tangent and between those two objects. Basically the method are the same as the first two command namely 2P and 3P but the only difference is that the points you will select are two tangents of the circle against the two objects and you will specify the radius ( See Fig. 3 Below).

 

    autocad polyline icon

Fig. 3 Drawing a Circle Using Tangent Tangent Radius or TTR 

To start making the circle, go to the menu and select Draw>Circle> Tan Tan Radius and AutoCAD will prompt: Specify point on object for first tangent of circle: In our example as you can see above, the first object is the line, which is you first tangent of the circle. Then after selecting the object, you will see an additional object snap icon, then click it. Again AutoCAD will prompt:  Specify point on object for second tangent of circle: The second tangent point is the arc in our example. Again follow the first step and click again. The third prompt will say: Specify radius of circle: which is asking you to give the radius of the circle you wish to create. The radius will depend on the size of the two tangential objects you have created or the distance between the two. You can try the value “2” for now if you don’t have an idea which value to put. There are other commands available on the menu: the Center, Radius; Center, Diameter; Tan Tan Tan which is only a derivative of the 3P, 2P and TTR. Those are just autolisp or macros created on the version 2000 I’m using. Maybe on the later versions like the 2001 to 2008 there are lots of commands available for creating the circle.

4 comments ↓

#1 Vivian on 03.08.11 at 7:53 am

Thank you for this! Very helpful!

#2 Kuanga Lenga on 03.12.11 at 7:35 am

Bulaaa…..Easy to understand and follow..thanks very much….Nakaaa

#3 Arba on 11.29.12 at 9:46 pm

Very useful

#4 hamza on 03.27.13 at 12:45 am

useful… but i have to ask about ttr more ..please elaborate with an other example 🙂

Leave a Comment