"Inflate" polyline or shape into 3D with constrained edges?

[daniel.simon]

I'm rather new to AutoCAD, and I've been trying in vain to convert some of my 2D Adobe Illustrator files into 3D.

The question I'm struggling with is how to "inflate" a polyline or other 2D shape into 3D with constrained edges around the perimiter. This image gives an example of what I'm trying to do:

Basically, pull/push an anchor point at the center of the polyline up in the Z direction, but keep the perimeter tied down on the XY plane. Think of blowing a soap bubble up through the polyline... 

Here's an example of what a colleage achieved in 3DSMax. I'm trying to recreate the three liquid drops indicated with the green arrows. The model shows liquid drops on a plastic (hydrophilic) surface.

Any ideas? I have a strong feeling I'm missing something very simple.

Thanks!

[dmfrazier]

Draw your polyline rounded RECTANGLE.

EXTRUDE it to the height you want at the center. (Make sure you use the Solid mode.)

FILLETEDGE all top edges with a radius that matches the extrusion height.

The result I got (with "vanilla" AutoCAD 2013) was "pretty close" to what you illustrated, but maybe you were asking for something a little different.

In any case, that's the best I can do on short notice (and very little 3D experience).

[daniel.simon]

Thanks for the tip. I tried your method and it does look close to what I'm trying to do... But, the top of the bubble still looks flat. Take a look at the attached DWG (and this export from it).

Any more suggestions?

[troma]

I have no 3D knowledge at all in this field, but I can understand the theory. And I can tell you that in theory, you need the section to be like half an ellipse. The way you are doing it gets you a flat top with a quadrat of a circle on each end, the way you want to do it would get you a semi-elliptical section.
In practice I have no idea how to achieve that, but there you go.

[dmfrazier]

I agree that the shape seems to be somehow derive-able from an ellipse (actually an ellipsoid solid), but I don't think it's quite half.  It's more like a sliced-off part of the solid, but even that doesn't quite cut it (pun intended).

If you can envision an ellipsoid (which comes easier to me than actually making one), if you take a slice of it you would probably be able to get the general profile, but I don't think you'd ever get the rounds at the corners. 

[daniel.simon]

Hmm... this is looking harder to accomplish than I thought. 3DSMax (and Maya) have deform functions that seem to handle this, but I can't figure out how to get it to work with AutoCAD. Any other suggestions?

In any case, thanks for the help!

[Anonymous]

I would extrude the rectangle to your required height, then create a solid using an ellipse as the bottom, extrude to the width of the recatngle, place over the rectangle solid and subtract the ellipse solid from the rectangle.

I hope this makes sense to you...

actually just tried with an ellipse, didn't work, so I approximated the ellipse with a pline.and you will need to subtract it twice (once in the x-y plane and once at 90 degrees to that)

[Anonymous]

tried to attach a tiff of the result. apparently it is too big to upload

[daniel.simon]

FSJ_Mo:

I don't really understand your method. Could you post your DWG?

Thanks!

[Anonymous]

Take a look at this and see if this is what you require.

[daniel.simon]

Ahh... I see what you mean, now. This looks much closer on the profiles, but the hard edges are still a problem. This really isn't an easy thing to do in AutoCAD, I guess. Maybe I just hit on one of the main differences between AutoCAD and Maya or 3DS...

Thanks for the help!

[Anonymous]

yes, still a little rough. That was a quick 5 minute sketch. I am sure with a little more work it could be better.

You're welcome

[dmfrazier]

I think this shape would have to have at least some flatness on the top, and it would probably be in the shape of an ellipse. 

Try this:

Draw your 2D polyline rounded RECTANGLE.

Draw a 2D ellipse that fits inside the rounded rectangle (the axes match the width and length of the rectangle).

Offset the ellipse the same distance (to the inside) as the max. height of your "drop".

3DMove the smaller ellipse so that it is that same distance "above" the rounded rectangle.

Use LOFT to create a solid with these two "edges".  Pick the rounded rectangle first.  In the LOFT command, use the special grips to adjust the draft angles until it looks the way you want it.

As an alternative to LOFT, try SURFBLEND.

I was able to get "better" results than the previous method, though it is difficult to get the ellipse on top to blend in fully.

[JDMather]

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@daniel.simon wrote:
This really isn't an easy thing to do in AutoCAD, ....

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...

Pretty easy in Autodesk Inventor.  And parametric.  Change dimension(s) and model updates.

[daniel.simon]

Thanks for the tip!

What do you mean "and parametric"? Is this something that can be done in AutoCAD, or do I need to switch to Inventor for it? Do you have a second to send me an example (if it's AutoCAD) or a rough outline of how to do this? I'm a beginner.

[JDMather]

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@daniel.simon wrote:

Thanks for the tip!

What do you mean "and parametric"? Is this something that can be done in AutoCAD, ...

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Parametric means that the dimensions drive the part (rather than being driven by the part).  So if you want to change the size of something you simply double click the dimension and the model updates to the new size.

Later versions of AutoCAD have 2D parametric - but not 3D.

I don't normally hang out here and only found this because I got lost.

Heading back to where I belong now, so long... http://forums.autodesk.com/t5/Autodesk-Inventor/bd-p/78

I posted an example there in the past week or so.