# How to make a "bulge" for seat cushions?

I’m trying to simulate the bulge or slight dome that seat cushions have on couches, and I’m not sure what the best method is?

I did figure out one way which is that I made 3 arcs across 3 parallel lines and then Loft between all three of them. Then I place that on top of a rectangular object that has fillets for roundness on the sides.

Does anyone know of an easier or better way to achieve the same effect? it’s a lot of effort just to “pull” out the surface of the pillow a bit.

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Have you tried ‘literally’ pulling out the surface?

You can draw a shape on the surface then use it to push/pull on the surface.

Of course I’ve tried just extruding sketches. I’ve also tried lofting from the surface to another sketch, and using fillets in various ways. None of those have achieved the curved/dome shape I’m going for.

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Try projecting contours as Edges onto the face. These edges can be transformed later on to get the result you are looking for. You can gain some control over the deformed faces by combining the projected edges.

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@KPeter_Shapr3D this is exactly what I wanted, thank you!

This projected Circle looks a lot like when I just draw a Circle sketch on the surface of the rectangular object. But it behaves very differently: if I just draw a Circle on the object, I cannot select the edge and move/rotate it (when I click the edge, it just wants to edit the sketch instead of allowing me to choose an operation like Move/Rotate).

Can you help me understand the difference between these two types of objects: A projected circle versus a circle drawn on the surface? They look and act similar, but clearly have some major differences.

Thanks!

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Sure!
The circle sketch is a sketch element that can only be planar. It is placed on the surface but does not have any further relation with it.
An edge on the other hand is a part of the face. It is considered to be a modeling element that can be transformed and so on. Please use it wisely as transforming these projected edges could easily end up in quite complex geometries.

Fun fact: projecting sketches to a curved face is a current workaround for 3D sketching. While sketching is only allowed on planar faces, edges can be curved along all three axes and one can use them as sweep paths or loft guides.

I apologise that my solution isn’t what you were looking for. I thought you wanted to bulge the surface.

In my video below you will see two solutions:

I drew a circle directly onto the first (red) rectangle, extruded it a nominal distance then selected the extruded body and pulled. You’ll notice that, after pulling, you can extrude back down to eliminate the body and leave a perfect bulge,

I projected a circle onto the second (blue) rectangle (just as @KPeter_Shapr3D did) but rather than extrude it in to a body I simply pulled it. You’ll notice that, after pulling, the original shape creates a flat top essentially truncating the bulge (great for buttons on futons I guess).

EDIT:
Please see the comment @PEC below.

It seems you can simply delete the projected sketch after pulling.
This didn’t work for me earlier hence the reason I posted a video with the two options.

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@welshsteve Steve, I love your technique shown on the left object. Not only is it faster/easier than the slower projection process, but you achieve a totally smooth bulge this way, without the flat surface (I was having to make the flat surface a really tiny circle with the method shown on the right, which was also a pain).

THIS is the best solution as far as I’m concerned. Many thanks!

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Hi,

as a complement to @welshsteve “blue” solution, you can also simply delete the flat surface after pulling or pushing the surface.

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Thank you @PEC

I actually tried this earlier but it simply wouldn’t delete, hence the two approaches.

After just reading your comment, I tried drawing it from scratch again and it DID delete. (There must have been glitch earlier.)

I will add an edit to my earlier post. Much appreciated

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Hi @jpeskin,

Please see the comment from @PEC below. It appears you can simply delete the projected shape from the ‘blue’ rectangle. I wasn’t able to do this earlier but when I retried… it worked!

So, either way is viable and depends on your preferred workflow.

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