# How to Draw This?

## Recommended Posts

Can someone please tell me how to draw a continuous curve like below pic (the blue curve) start from point A through point B and end at point C.

The one I had drawn on above pic is not continuous at point B. It's like a two different curves, the A-B curve and B-C curve, joined together at point B.

Edited by basty

##### Share on other sites

There are a few ways to get that done, but the important point is if you want it to be continuous the two arc centres should be on a straight line that passes through the tangent point. I placed the yellow dashed circles first to find the lower arc's center point, that gives you 2 points for drawing the straight green line, then you just have to find the point on that green line for the upper arc.

And this way starting from the top arc

The dwg is for the first method, I'll let you figure out the points for the second

Tan.dwg

##### Share on other sites

The shape of B-C arc is not what I want.

The shape is too concave.

As you can see, the B-C arc intersect C-E hidden line at D and C-D arc is exceed the C-E hidden line.

This is not what I expected.

The one I expect is that the B-C arc does not exceed the C-E hidden line.

From what I see is, you draw the A-B arc first than next you draw the B-C arc.

What about if I draw the B-C arc first then next the A-B arc?

Can you show me this method by an image like above?

This is the dwg file for you.

continuous_curve_02.dwg

Edited by basty

##### Share on other sites

Use the same method as the first option if you use the ray command pick the start point as the center of your arc and the second point is B, then the center of your arc AB is somewhere on that line.

##### Share on other sites

It is easy enough to draw continuous arcs, but there are many solutions to the measurements shown in your diagram.

You need to give more information or another dimension to get it how you want it to look.

##### Share on other sites
It is easy enough to draw continuous arcs, but there are many solutions to the measurements shown in your diagram.

You need to give more information or another dimension to get it how you want it to look.

The blue arcs is the same as steven-g made, no.

The shape of magenta arcs is weird.

The green arcs is my best choice.

Can you show me how to make the green arcs continuously?

##### Share on other sites
Can you show me how to draw the green arc?

How about you follow the advice that was given first? "You need to give more information or another dimension to get it how you want it to look."

##### Share on other sites

I offset the top line upwards by 1 (the actual offset distance is not important) so that point A is vertically above point B. This ensures that the tangent at B is vertical.

Now draw a line from A to B. End the line command and start the arc command. When the start point is needed (look at the command line), just press Enter. The arc will now start drawing from B with the tangent vertical. The endpoint of the arc is point C. Start the arc command again, and again when it says "Specify start point of the arc", merely press enter. A new arc will start, tangential to the previous arc. The end point is D.

Erase the temporary line AB.

##### Share on other sites
How about you follow the advice that was given first? "You need to give more information or another dimension to get it how you want it to look."

All dimensions were already provided in post #1.

##### Share on other sites
I offset the top line upwards by 1 (the actual offset distance is not important) so that point A is vertically above point B. This ensures that the tangent at B is vertical.

Now draw a line from A to B. End the line command and start the arc command. When the start point is needed (look at the command line), just press Enter. The arc will now start drawing from B with the tangent vertical. The endpoint of the arc is point C. Start the arc command again, and again when it says "Specify start point of the arc", merely press enter. A new arc will start, tangential to the previous arc. The end point is D.

Erase the temporary line AB.

Can you show me how to draw these green arcs by graphical method like steven-g did in post #2?

##### Share on other sites
All dimensions were already provided in post #1.

Please show me where you provided the curve information for the arcs themselves. I must have missed that post.

##### Share on other sites
All dimensions were already provided in post

That is patently not true, because I was able to draw four different sets of arcs without really trying

Can you show me how to draw these green arcs by graphical method like steven-g did in post

Only if you provide more information about what is the tangential directions at the ends or the arc radii. I have actually shown you the way to draw using the facilities provided by AutoCAD. In many instances this allows one to bypass the graphical constructions, and the ensuing tidying up.

##### Share on other sites

basty: In your first post you asked about drawing a "continuous curve". Yet, in subsequent posts it appears we are talking about two distinctly different arcs. The only way I know of drawing the two curves and keeping them "continuous" would be via the Polyline command using the Arc option and subsequent options that apply only to arcs themselves like Center.

##### Share on other sites
Please show me where you provided the curve information for the arcs themselves. I must have missed that post.

Do you mean you need the dimension of the arcs?

If so, I use a graphical method to draw these arcs, not by dimension.

##### Share on other sites
basty: In your first post you asked about drawing a "continuous curve". Yet, in subsequent posts it appears we are talking about two distinctly different arcs. The only way I know of drawing the two curves and keeping them "continuous" would be via the Polyline command using the Arc option and subsequent options that apply only to arcs themselves like Center.

Yes, at first all I want is a "curve". But steven-g show me an "arcs" instead of a "curve". So I just follow him anyway. Btw, I don't know if a "curve" is same as "arc"?

##### Share on other sites

Arc data is what I am looking for and what you failed to provided. Drawing the arcs graphically as you admit to doing means there could be any number of possible solutions depending on who is doing the drawing. You might as well ask us how to nail down jello.

##### Share on other sites

Only if you provide more information about what is the tangential directions at the ends or the arc radii. I have actually shown you the way to draw using the facilities provided by AutoCAD. In many instances this allows one to bypass the graphical constructions, and the ensuing tidying up.

What is "tangential directions" and "arc radii"? I am not familiar with these terms.

Can you show me by image?

##### Share on other sites

You should already be familiar with such terms as radius, chord, length of curve, tangent, central angle, etc. as part of your schooling. Didn't you study such things as horizontal curves and reverse curves?

##### Share on other sites
Arc data is what I am looking for and what you failed to provided. Drawing the arcs graphically as you admit to doing means there could be any number of possible solutions depending on who is doing the drawing. You might as well ask us how to nail down jello.

If you still want to know how I draw the arcs is such as below.

1. Draw a green circle with its center at point B and radius of B-C.

2. Draw the yellow circle with its center at point C and radius of B-C. The green circle and the yellow circle will intersect at point D.

3. Draw a circle with its center at point D and radius of C-D (or B-D).

4. Trim the circle in step 3 so that we get the blue arc.

See below pic for more detail.

##### Share on other sites
You should already be familiar with such terms as radius, chord, length of curve, tangent, central angle, etc. as part of your schooling. Didn't you study such things as horizontal curves and reverse curves?

The one I already familiar is radius, chord, tangent, and central angle. I did learned how to find the length of a curve in calculus.

The "radii" term is not common and what I was thought is using a "radius", not "radii".