Rhino 3D: how to convert curve to cookie cutter

[pyronaught]

Using Rhino 3D, does anyone know how to take a closed curve and convert it to a solid extrusion which has a consistent wall thickness around the entire perimeter? This is easy for things squares or circles that have symmetry around the axis of extrusion, but not with shapes like hearts or rectangles because they don't scale equally in all directions. With a heart shape for example, you can't just clone it, 2D scale it slightly smaller and Boolean subtract it from the core of the original and have the same wall thickness around the perimeter of the resulting object because the heart curve will not scale equally in all directions from its center point. I'm using the area centroid finder to pick the center point of the scale operation but it just doesn't produce a second inner curve where the distance to the outer curve is exactly the same around the entire perimeter. Note in the image below how the area where the two curves come together have a narrower separation than other parts of the curve. I've had this same issue trying to make fabric seam allowances on rectangular balloon panels too-- you just can't create a copy and scale it around the center point, it won't produce equal expansion from the original edge at every point. Is there an easy trick for doing this?

problem1.jpg (130.39 KiB) Viewed 13498 times

[pyronaught]

I found one way for the cookie cutter type example is to create a thin rectangle representing a cross section of the wall, then use Sweep1 command to sweep it around the perimeter. For the heart example you have to have the "Untrimmed Miters" option checked to keep from creating a mess, then you still have to slice off some weirdness that occurs on the two ends to get the final cookie cutter. I'd still like to know how to take the edge of a 2D curve and create an equally scaled clone of it in the same plane though.

[Jules]

Did you try the Shell function in the Solids palette? Makes a perfect shell, and you can specify how thick you want it to be.

[pyronaught]

I'm not seeing the shell option in my version 4 Rhino, I wonder if only version 5 has that? Is that option right off the Solid menu or is it a sub-menu under something else on that menu?

EDIT: I just checked, it's not in Rhino 4

Another reason to upgrade I guess. Have to wait till my wife is in school again so I can get the educational version, otherwise it's a $430 upgrade

[jsc]

In most modelers I'm familiar with, there is a sketch offset command. Looks like Rhino has one, too: http://docs.mcneel.com/rhino/5/help/en- ... offset.htm

[PcS]

Couldn't you just 2d or 3d scale the object ?

[Jules]

I'm not seeing the shell option in my version 4 Rhino, I wonder if only version 5 has that? Is that option right off the Solid menu or is it a sub-menu under something else on that menu?

EDIT: I just checked, it's not in Rhino 4

Another reason to upgrade I guess. Have to wait till my wife is in school again so I can get the educational version, otherwise it's a $430 upgrade

Ugh! You'd think that was a fairly basic function, wouldn't you? Maybe you'd just need to update? (Sometimes they hand things like that out in the updates, as opposed to paying for upgrades.)

Jin's right though, if I didn't have a shell function, i'd try the Offset function. (Or....Do you have Illustrator? I've found it's sometimes easier to create the shell in that, take it into Rhino through the Import function, then just extrude it as a group. Rhino will subtract the center shape out if you extrude them at the same time.)

Just need to watch for one thing when you do that though - sometimes a curve is created on either side of a line imported from Illustrator. Just delete one of them before you start doing extrusion functions or anything related to Boolean unions/differences. It gives weird results and fails if you don't remember to get rid of one of the two.

[pyronaught]

Couldn't you just 2d or 3d scale the object ?

The image above is what you get with the 2D scale. The distance between the inner and outer perimeter are just not equal at every point when doing it that way, except in the case of a circle.

[pyronaught]

In most modelers I'm familiar with, there is a sketch offset command. Looks like Rhino has one, too: http://docs.mcneel.com/rhino/5/help/en- ... offset.htm

That's totally what I was looking for, thanks! Even if there are better ways of making cookie cutter shells, that offset feature is definitely the best way to extend 2D fabric panels or metal sheets to allow a margin for seams.

[pyronaught]

I'm not seeing the shell option in my version 4 Rhino, I wonder if only version 5 has that? Is that option right off the Solid menu or is it a sub-menu under something else on that menu?

EDIT: I just checked, it's not in Rhino 4

Another reason to upgrade I guess. Have to wait till my wife is in school again so I can get the educational version, otherwise it's a $430 upgrade

Ugh! You'd think that was a fairly basic function, wouldn't you? Maybe you'd just need to update? (Sometimes they hand things like that out in the updates, as opposed to paying for upgrades.)

Jin's right though, if I didn't have a shell function, i'd try the Offset function. (Or....Do you have Illustrator? I've found it's sometimes easier to create the shell in that, take it into Rhino through the Import function, then just extrude it as a group. Rhino will subtract the center shape out if you extrude them at the same time.)

Just need to watch for one thing when you do that though - sometimes a curve is created on either side of a line imported from Illustrator. Just delete one of them before you start doing extrusion functions or anything related to Boolean unions/differences. It gives weird results and fails if you don't remember to get rid of one of the two.

It looks like they added a lot of stuff in Version 5. I have the latest update of version 4, but beyond a certain point updates are just bug fixes and all the new stuff goes into the next major release.

I've imported 2D patterns from Corel Draw like that, but have been doing less and less of that the better I get with drawing 2D shapes in Rhino. My version of Corel dates back to the 90s too, so its very outdated. They don't let you update just Corel Draw, you have to buy the whole suite of tools and pay for a bunch of stuff you don't need, so I never bothered to update it. I switched over to a cheaper vector drawing program called Xara that is pretty decent and has a better user interface than Corel.