Adding thickness to a curved surface
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Is there a smart way to add thicknessto a curved surface, say a hemisphere...in other words to create a hemispherical shell with thickness. The push/pull tool only seems to work on plane surfaces.
I can see that such a shell could be made from scratch as an object of rotation, but...what if one already had (for example) a hemispherical surface of zero thickness?
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I think the best you could do is to use the follow me lathe tool.
Maybe you could possibly copy it, scale it up a bit, then align it over the original object, although I dont think this would work in every case.
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It can be done as you say by copying, scaling and repositioning, but it is quite fiddly!
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Hi caddit.
I think masta has the right idea but I would use the off-set tool first and only then I'd go with the follow me tool.
Have a look at the picture.
Is that the sort of thing you're looking for?
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Guys,
Starting with a shape that follows a circle works if you want to start with that.
With an existing hemisphere though that copy/moving, resizing (about the center!) and moving back to align should not take more than a few seconds so what Masta say does indeed work (even with more complex shapes; this is how I usually give some thickness to boat hulls for instance).
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I've been playing around with Gidon's method and it seems like the follow me tool produces some strange results. In Gidon's diagram you can see that the shape has a "V" cut out of it at the top. This generally seems to be the case. In fact I would be interested to know if it is possible to make a perfect one-eighth-sphere (solid or hollow) using just the follow me tool.
It seems like your method is the way to get a precise result, Gaieus. And also, it looks like the best way also to give thickness to complex curves, like as you say boat hulls.
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Caddict, the hole in Gidon's picture can be due to the model being very small (and with the follow me tool or during intersecting some really small faces do not create in SU thus the usual workaround; scale the whole model up and work that way - at the end you can scale it back).
Now with the follow me tool to create a quarter sphere (or half dome) for instance, there is the problem that the ending segments of the half circle you want to create are not perpendicular to the halving diagonal (if you are creating it from endpoint to endpoint) just "tangent" as a curve. Therefore the last segment will be over-extruded (actually normally following the perpendicular way SU thinks the extrusion should go) and you end up with a crooked top part.
You can either intersect it away or better to draw a full dome (hemisphere), turn on hidden geometry and delete the unwanted half.
One gets used to it quite soon...
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Dear Caddict,
You might try the following for a simple sphere.
Create the sphere and make it a component. Double click on the sphere component to go into edit mode. Triple click on the sphere while in edit mode to select all and then execute the copy command. Come out of the edit mode (click outside the component box), go to the Edit drop down menu and select 'paste in place'. This will give you a sphere as a component, overlaid with a second sphere which is not a component, the latter highlighted immediately after executing the 'paste in place' command. Select the 'scale' tool and make the highlighted (non-component) sphere larger or smaller. Select all and explode if required.
To verify that a double sphere exists, use the section tool.
I do not know if this technique will work with more complex shapes, like the hull of a boat, but it has its place in the grand scheme of things.
Kind regards,
Bob -
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Wow I feel like I finally contributed on here after all this time!
But, it may have some issues with complex shapes for example, but I can only think of a few cases offhand where it "might" not work. Oh, and thanks for the tip to get rid of those stupid small faces not being present when using follow me. I cant believe i didnt think to just scale everything up alot while working.
The problem I have now is finding time to do stuff, i pretty much work 7 days a week now. The only things I have time to do now are models of desks and tables and stuff that Ive been wanting to physically make. Its just too bad that I dont have time to head out to use my Grandpas woodshop or Id have me a really nice computer desk I think.
As far as creating 1/8th of a sphere goes i think you can get away with using the follow me, then deleting a bunch of extra geometry. The way I do it though is make a half a sphere then draw a couple faces through it to bisect it twice. That leaves me with one fourth of half a sphere, which is the 1/8th sphere you were talking about if im not mistaken.
You can either create the shape in place (which is a hell of a mess) or figure out a method that works for you to keep it aligned while creating the shape at another point. Then just move it into place. The latter isnt too hard.
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Thanks Guys for the input. I have to say this is a great forum!
What I am really trying to do is to model a dome-shaped roof. The geometry is not regular, so I plan to make the basic curve with sandbox tools. Then it will need thickness. So it looks like the copy, scale method will be the one. Bob's system is very clean and economical although the problem still remains to unify the two skins into a single solid object. This is covered by Jean in Scene 6 of his how-to...just by adding a few lines. I guess one might also resort to the method suggested by Masta of intersecting the object with planes and then trimming.
The thing about making a perfect one-eighth-sphere with the follow-me tool is just out of curiosity, but for me it sheds some light on how the tool actually works.
@unknownuser said:
Therefore the last segment will be over-extruded (actually normally following the perpendicular way SU thinks the extrusion should go) and you end up with a crooked top part.
Gaieus, I thinks that sums it up.
PS I didn't follow your explanation about the hole in Gidons picture and scaling up.
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@caddict said:
. . . I didn't follow your explanation about the hole in Gidons picture and scaling up.
There's an oddness in SU that I don't know the reason for, but which is definitely there.
If you make a complex model with curves and intersecting lines and the whole thing is small, like a few centimeters across, SU will have trouble filling in some of the odd triangles which are created. And, you won't be able to fix them reliably.
If you select the whole thing and scale it up, say by a factor of 100, making it a few meters across, you won't have that problem. After you have done the editing, you can scale it back down by a factor of .01 and it will be perfect and to scale.
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Thanks John
I have been experimenting with that and I get it now. The scaling is a useful trick.
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I have to have shell element with thickness in order for me to export out for Finite Element Analysis, I appreciate it if anyone can help.
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