Trying To shell this shape

Hey all ive been using the shell command with great success but with this shape its just not working. I attached the Project, i basically just was to make all the faces 18mm thick and miter joint where the corners all meet so i can lay them out and CNC cut them. any help on a method to do this would be so awesome as ive been at it for house with no success.

Help Me.3dm (74.1 KB)

Thanks :smiley:

Hello - if you Join all the surfaces, MergeAllFaces then OffsetSrf, solid=Yes toward the camera (in your image) it should work…


I tried that method before its doesnt work im afraid but thank you.

Thought id stick this example up to better explain what im trying to achieve at the joins :smiley: !
This was done using the Shell command.

You’ll have to model the mitre surfaces yourself.

Unless you’re planning to change the shape 20 times, a manual approach is the most efficient way.

Hi Brangruff

Help Me solution.3dm (204.9 KB)

Please see attached file, I think you can’t use shell opt on opened objects, you need to closed them.

Hope that’s help

Hey man thanks so much for taking the time. This is the first way i tried and im afraid it doesnt work. I need it to be 18mm thick and i need all the joints to come together perfectly so i can lay the exploded solid faces out for cnc cutting. You can see in the simple example i made with the pyramid the kind of join between the faces im looking for (mitre)

is this what you want?Help 2.3dm (184.8 KB)

Did you use the shell command ? This is very similar to how i tried to begin with but you get weird little imperfections. ull see its looks fine but then when i explode the shape to lay out the panels for cnc there are weird little things.


Yes I did shell…

I closed off the shape to make it a “solid” then i shelled that solid

not sure why you are getting that weird corner? or what you are really going for. when i explode, everything is fine. what are you cncing? out of what? is this a bent metal?

Do you really need the thickness if you are cnc’ing ?

also have you tried something like dupfaceborder to just get the curves to cut? you can make2D, rotate3d, orient, setpt or whatever to get them all in top view and flat for cutting files…

The pic of the corner was taken from the file you sent me :smiley: i want to cut this out of 18 mm ply wood and have all the joins mitred.

Shelling the other direction, by boxing out the other side of the surfaces, will avoid the problem corner, but it will also create other problems.

This whole task looks like it should be easy, but it isn’t easy. Maybe there’s a grasshopper definition that can do it? The part that gets tricky here is that there are convex and concave folds.

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One more thing: i played with mitering this manually, and will upload later.

Important thing to note: The reason shelling the form is giving you some short edges is that it’s geometrically impossible to create “perfect” miters from your surfaces and also maintain a top on the final form that is parallel to the Z plane. There will be small truncations on a few of the final pieces.

So, because Shell didn’t seem to work, and OffsetSrf didn’t seem to work, I decided to see if I could do a shell and miter of this polysurface manually.

Here’s what I figured out: there’s no way to make perfect miters at the vertices where four edges meet. A miter must bisect the crease angle or it isn’t a miter, and the opposing faces will have different widths, so there is no wiggle room or fudging to be done here.

What can be done is to compromise by setting priorities.

If you offset all these faces individually, and then scale them 2d, and then split them with planes that bisect the crease angles, you’ll get surfaces that extend too far or not far enough in the locations where you would want them to meet. You could just lop off the points that stick out too far, but if you do that the wrong way, and you’re working with sheet stock, you’ll end up exposing the interior of the sheet stock.

But if you do it right, you’ll get some odd looking angles while maintaining the veneer all the way around the object, like this:

What this has illuminated for me is that the reason _OffsetSrf and _Shell glitch out so often is pretty straightforward: the tasks they do are hard and have a lot of variables. This is also probably why we don’t see a lot of complex plywood origami out there in the real world. Also: the document tolerance for the original file may be too big.

Anyway, here’s the file, with all the miters done:helpMe.3dm (255.6 KB)

CNC routing this will require more than a 3 axis machine, and even on a 5axis machine, you’ll need steep v-bits to get the inside miter corners right.

IF this had been all quads, it would’ve been much, much easier.

Also, if anybody knows of any grasshopper definitions or threads that try to tackle this kind of task, please let me know. Plywood origami interests me very much.

@kunf @zale_orcid

wow thanks man thats a lot of work. i wish i had your brain :stuck_out_tongue:

Hello All

I was thinking about how other way I would be able to do this.
Here is my result, I think is pretty much close to it :wink:

Tell me what do you think about it.
Help Me solution.3dm (293.7 KB)

Have a great weekend everyone !!!

You created non-planar surfaces by merging the triangular faces.

Hi Max

You are right, didn’t noticed it,
but it’s not a problem to replace these merged ones.
By using edge curves opt.

Help Me solution.3dm (351.0 KB)

hell yea @Max3

yea the whole time I’m thinking this isn’t going to work with a 3axis…

nice work