Stretch action on ellipse in dynamic blocks

[pratikk20990]

Hi, I want to stretch a ellipse (not 2D polyline) in AutoCAD Dynamic blocks but not able to achieve it. Any suggestions on how to implement it?

The grip on ellipse can be modified manually while editing dynamic blocks but the stretch action does not move that grip handle.

Screenshot is attached.

[j.palmeL29YX · Accepted solution]

I'd do it using parametric constraints (and dimensions) as shown >>here<<. 

A sample dwg attached.

[pratikk20990]

Hello,

Yes this is exactly what I want to do. Thank you so much for sending your acad file.

Kindly explain a bit as well that how you did this as I can see just two geometric constraints in your file .

Also, how you picked up the top point of ellipse while placing a dimensional constraint there? When I try to do it by activating the quadrant option while placing dimensional constraint, it says invalid point.

[pratikk20990]

Okay, I have figured out most of the things.

Just a few questions:

1. What is the role of collinear constraint on ellipse and rectangle line? Any particular order in which the two objects shall be selected?

2. What is the role of parallel constraint on ellipse and tangent line?

3. How you made that tangent line invisible in model?

[j.palmeL29YX · Accepted solution]

A >>video<< what I did, and some explanatory words: 

First we need a geometric stable model, because later we want to change some dimensions, but we have to make sure that the rectangle always remains a rectangle, and the half ellipse always remains a half ellipse, touching the rectangle. 

Adding some geometric constraints I reduce step by step the unwanted degrees of freedom

- constrain the opposite lines of the rectangle parallel

- constrain two touching lines perpendicular

- constrain one of the lines horizontal 

=> You can drag wherever you want, the rectangle stays a stable one.

[j.palmeL29YX · Accepted solution]

Ignore the previous post (#5). my laptop went on strike for a moment (suddenly I lost the internet connection).

I hope now it will work fine.

Here a >>video<< what I did, and some explanatory words: 

First we need a geometric stable model, because later we want to change some dimensions, but we have to make sure that the rectangle always stays a rectangle, and the half ellipse always stays a half ellipse, touching the rectangle. 

Adding some geometric constraints I reduce step by step the unwanted degrees of freedom: 

- constrain the opposite lines of the rectangle parallel

- constrain two touching lines perpendicular

- constrain one of the lines horizontal 

=> Now you can drag wherever you want, the rectangle stays a stable one.

- constrain the endpoints of the ellipse coincident to the endpoints of the upper line 

=> Now we have still an unwanted vertical movement of the ellipse. This we can remove by adding a 

- collinear constraint between the main axis of the ellipse and the upper horizontal line of the rectangle. 

=> Now we have a geometric stable model that only has the desired and required degrees of freedom. 

(of course, we can do all this so far also in the block editor).

Next we can add the needed dimensions in the blockeditor. 

No problem for the dimensions of the rectangle. 

But the ellipse doesn't have a point for adding the wished dimension. 

Workaround: 

- I add a helpline, 

- constrain horizontal

- constrain coincident the endpoint to the object ellipse. 

- constrain this point vertical to the midpoint of the rectangle. 

=> The line is restricted to the upper quadrant point of the ellipse. 

Now we can add a dimension to the endpoint of this helpline. 

At the end we convert this line into a construction line (which always is invisible in the block references) as shown in the video.

HTH

[Pawel_Marchewka]

There is also another way - You can't stretch ellipse but You can stretch two halves of it. However this works with halves, but not 1/4 of ellipse. Maybe this will be usefull for somebody LT positive.

[g1nchh]

Try this dynamic block for an ellipse. it works for me. 

Basically, following some of the principles in the thread.

Could be cleaned up a little more to create only one line per ellipse quadrant

[j.palmeL29YX]

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@g1nchh wrote:

Try this ... it works for me. 

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For the moment it may work well. But this mixture of dynamic parameters/actions and constraints is not recommended. 

Assuming you want to add a Rotation Action at a later time - see what now will happen: 

SCNR