[Edit: How do people know what 2D shapes go together to make certain 3D shapes when *making patterns.]
I know if someone wanted to sew a cube, they would cut 6 squares and sew them together. If they wanted to sew a pyramid, they would cut 1 square and 4 triangles.
But what about weird shapes like with stuffed animals? If someone had never seen a sewing pattern for a teddy bear in their entire life, how would they know what shapes to cut and sew to make the teddy bear?
(It seems simple in concept, but it’s hard to imagine how certain shapes would come together to create something like a humanoid doll.)
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There’s always practice :-). They’re not making the world’s first teddy bear, and I’m sure someone’s botched one before figuring out exactly how to proportion things.
Also fabric stretches and warps a bit. A pillowcase, for example, is just two rectangles sewn together, but stuff it and the flat pieces of fabric bend to make a plump, firm pillow.
It’s kinda like putting together a puzzle! Imagine you have a bunch of flat shapes, like squares, triangles, or circles, and you know that when you fold them or put them together in a certain way, they can turn into something that’s 3D, like a box or a ball. When people sew, they look at the flat pieces of fabric and know how they’ll bend and join to make that 3D shape because they’ve practiced or seen it before, just like how you might know which puzzle pieces fit together to make a picture.
So when sewing, they imagine how the flat fabric will turn into a stuffed toy or piece of clothing, kinda like imagining how puzzle pieces fit together to make a whole shape!
As someone who has attempted making plushies and stuffed animals by hand with no pattern, I can say firmly that you do not know what 3D shapes will be formed from 2D shapes until you start sewing the edges of fabric together. And then you learn some general patterns visually when you see what they turn into. And *then* you wise up and Google that shit dot com because so many people way smarter than you have already done that math and geometry, and much of it is available for free!
I think it’s important to realize that basically nobody starts with that, it’s a skill you can build up over time. If you’ve made a bunch of sleeves you’ll probably start knowing the basic shapes for drafting one. For trying something new, some people start with a mockup to play around with the shape before using the good fabric, or I’ve even seen people make mini versions out of paper to test. Basically it’s something people pick up with experience.
Think of a video game character from the early Playstation/ n64 era, that are all blocky and look like they wer emade with building blocks. Now think of a three dimensional figure of character from a modern video game title. That seemingly realistic figure is a mesh of triangles – with enough triangles, you can make practically smooth looking shapes.
People who sew are good at combining shapes like those videogame artists are, but in the real world using pieces of fabric.
This is going to seem like a slight digression, but the connection makes sense to me.
So there’s a YouTube channel called Bad Obsession Motorsports where a couple of English blokes are building a heavily modified Mini, to the point where they have custom built virtually every single bracket on the car themselves. They cut and fold bits of cardboard to fit the part into the right spot on the chassis, then flatten the cardboard out and use them as a template to cut the metal into the right shape and size, then weld it together. Sometimes there’s more than one iteration but they’ve been doing custom work for a long time so are pretty good getting it right first time.
My experience in high school sewing was essentially the same – if you look at the patterns for say a t shirt you can sort of see how it all fits together and could imagine someone with a dressmaker’s mannequin working out what shape and size each piece has to be (and even how many pieces are required) by doing a similar thing with pieces of material – placing it where it needs to go on the mannequin and using pins to take it in where required. They would perhaps mark the required shape and any cuts to get the correct fit, then unfold it all and cut/sew the individual piece of fabric to fit into the garment as a whole.
Imagine polygons on 3d models. 3d shapes can be broken down into a collection of flat surfaces. a video [like this](https://youtu.be/o8_Rqbqx8u4?si=DCFv_6FcIh8RY29v) might help you visualize that translation to fabric.
Skill and experience, for the most part. When making clothes, there are plenty of pattern making techniques and lots of books on the subject.
Making stuffed animals is harder. The last time I did that, I built a mockup out of cardboard and masking tape and then cut that mockup apart to get a starting point for patterns. Then into CAD and then print a final pattern.
So you make a proto-type shirt, put it on a mannequin, keep adjusting it until you like it, then use that and panel it out so you can mass produce it.
Same with anything. Proto-type then figure out step by step how to assemble.
This is how I made panels for a vest for my son’s cosplay. Form fit one of his shirts to him with duct tape and panel it out. I still have the pieces of poster board for all the panels with adjustment edges if I need to enlarge it should I need to make another.
I guess the other thing would be to break the overall shape down into smaller shapes, so a teddy bear might be four long cylinders (or cones) for the arms and legs, 2 small cones for the ears, one wider but flatter cone for the nose and 2 spheres/flat cylinders for the head and body. Cones have a round base and a triangular shape for the top, and cylinders have 2 flat circular pieces and 2 rectangular pieces. A sphere is potentially more difficult, but depending on the material and stuffing you could probably get away with 2 flat circular pieces sown together and stuffed, like a pillowcase as another commenter said.
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