topic Re: Equal curve between two straight lines in AutoCAD Forum

Equal curve between two straight lines

m_kingdon — Fri, 15 Apr 2016 11:20:59 GMT

Hi all,

Is there an easy technique for drawing a double curve of radius x between two parallel lines?

I currently offset the lines by x and then draw a circle from the centre of the offset line with radius x. This gives me the two curves but I can't line them up perfectly and I ususally have to eye them in a add a small straight section in the middle. Is there a better technique?

Re: Equal curve between two straight lines

Alfred.NESWADBA — Fri, 15 Apr 2016 12:31:35 GMT

Hi,

look to the attached drawing using parametrics (especially tangential ones), is that what you are looking for?

Stretch the lines, modify the radius, just play with the grips of these objects.

- alfred -

Re: Equal curve between two straight lines

Kent1Cooper — Fri, 15 Apr 2016 17:11:34 GMT

You don't need the Offsets. Draw a Circle of the desired radius around the end of [or anywhere on] one of the Lines. Draw another Circle using the TTR [Tangent-Tangent-Radius] option, pick on the first Circle and the other Line in the general vicinities of where the new Circle should hit them, and give it the same radius value. Trim/Extend/Stretch as desired for the final positioning.

EDIT: Or, if you need the endpoints of the Lines to remain where they are, and don't know what radius is needed, draw an Arc starting at the end of one line, choose the End option and M2P Object Snap to the Midway-between-2-Points location between the Line endpoints, then the Direction option and the direction of the Line [in your example, 0 or 180, depending on which Line you started on].

Re: Equal curve between two straight lines

Anonymous — Fri, 15 Apr 2016 21:21:40 GMT

Not sure if the curve radii are important? If you have two endpoints at specific locations and you just want the smoothest s-curve between those two points then you can use the BLEND command. Select the lines and AutoCAD inserts a spline that is tangent to the lines.

Re: Equal curve between two straight lines

3wood — Sat, 16 Apr 2016 00:48:20 GMT

Just one simple command ARC can do the work perfectly.

Step 1, ensure the UCS parallel with the line objects.

Step 2,

Draw an arc from A, end point at C (middle point of A and B), with Direction option selected as below:

The result of Step 2:

Draw another arc from Point B, end at Point C, similar way as in Step 2.

Re: Equal curve between two straight lines

Kent1Cooper — Sat, 16 Apr 2016 13:05:41 GMT

@3wood wrote:

Just one simple command ARC can do the work perfectly.

....

Draw another arc from Point B, end at Point C, similar way as in Step 2.

That's what I described in the second part of Post 3, with the addition of the UCS setting if the Lines are not orthogonal in the current Coordinate System.

For the second Arc, though, it can be even simpler. After drawing the first Arc, you can hit Enter to recall the Arc command, and another Enter which will give you a tangent-continuation direction from the end of the first Arc, asking for the end point, and all you need to do is pick the other Point A. The same works if you have just drawn anything else directional -- draw a Line, then Arc and another Enter, and it will give you tangent continuation from the end of the Line you just drew.

Re: Equal curve between two straight lines

Anonymous — Sat, 16 Apr 2016 15:28:27 GMT

You can use spline fit from draw panel like this:

Then draw spline fit it will look more comfort than arc (streamline):

How look like ? good idea or useless???

Re: Equal curve between two straight lines

Kent1Cooper — Sat, 16 Apr 2016 20:47:19 GMT

@Kent1Cooper wrote:

You don't need the Offsets. Draw a Circle of the desired radius around the end of [or anywhere on] one of the Lines. Draw another Circle using the TTR [Tangent-Tangent-Radius] option, pick on the first Circle and the other Line in the general vicinities of where the new Circle should hit them, and give it the same radius value. ....

I mis-spoke in that description. Draw the first Circle not "around the end of...one of the Lines," but so that it is tangent to one of the Lines, whether you do that by:

1. Offsetting the Line to get the centerpoint [part of your original procedure], or by:

@2. using the 2P option in the Circle command and giving it a Line endpoint and then, with horizontal Lines as in your image, @0,[diameter] or @0,-@[diamter] or @[diamter]<90 or @diamter<270 for the second point, or by:

3. drawing it with its center at the end of the Line and then Moving it so that its curve lies on the Line [with horizontal Lines, up or down by the radius], or:

4. with the involvement of OSnap Tracking.

Then draw the second Circle with the TTR option, and Trim/etc.

Not having heard back from the OP, I couldn't say for sure, but I suspect most of our other suggestions [involving keeping the Line endpoints where they are] are irrelevant, because of the phrase "of radius x" in the first Post.

Re: Equal curve between two straight lines

m_kingdon — Wed, 20 Apr 2016 09:36:23 GMT

Hi all,

Thank you all for your responses to my question. Sorry for the delay in my reply, some drawing were due to go to planning so I was very busy.

The radius of the circle was something that had to be specified due to having to meet highways design standards.

The method of drawing one circle with the specified radius, then drawing the second using a TTR circle works great.