Extracting a dome from a cylinder

Hi, I want to extrude a dome in repetition all around a cylinder. any ideas??

rodillo.skp (1.5 MB)

Use a radial array. Copy move(tap ctrl for copy) the first one, then type the number of repeats you want.
Radial array


Awesome, thanks so much. but the tricky part is that I need the series of domes to be extracted from the cylinder. so the cylinder would have a series of domes inside the body of the cylinder…
see picture for idea. thanks!

On my phone now so can’t make a gif.
Easiest would be to make a ring with a segment count that matches the number of dents you want, then intersect one dome with one segment then radial array it.

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mmm. will try that…if I can…lol

The method above works. I create a short cylinder, extruded a single dome and then radial’d it around half as many times as are segments in the cylinder. Option copy the extruded cylinder on top of itself and rotate it 15 degrees to create the offset. Solid tools to join the two cylinders and then create as many copies as you want. Join them all. Done.


Wow. that`s it. the extrusion of the dome is what I haven’t been able to do it. how did you do that! ?? thanks so much

Extrusions can be tightened up to closer reflect your picture. One important thing I forgot to mention is to make sure to put a base on your dome so that it is solid and make the cylinder a solid (if using solid tools). This can be done with native tools too, but it requires a lot of intersecting of faces and deleting unneeded geometry.

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what plugin do you use for solids?

You shouldn’t need any plugins, I was aware you had ‘Make’ so didn’t mention solid tools, which are only available in pro.
You can intersect the dome with a face and easily remove the parts you don’t need, then build the whole thing from there with arrays.


I’m just having a lot of trouble intersecting and keeping it a solid. watching a lot of videos, but still…

Here’s a quicky. You need to understand the structure of the geometry. Here I have used a 48 segment circle to make 24 dents offset. and reduced the segment count on the dents for ease of use.

Because everything lines up on the relevant flat faces you can shift the dents down or up easily.


Create a group for your cylinder and your Dome. Drop your dome into your cylinder, making sure to turn on hidden geometry and align the groups along a common axis (red or green). Staying consistent with the axis is key in the creations of your geometry and in combining the groups.

Once you have the dome positioned, explode both groups. Select everything that includes the dome and “Intersect Selection”. Now you will be able to delete the extra dome geometry and the dome faces that were created.

You may have to reverse the face of the indentation (make sure to turn off hidden geometry to make this easier).

![Screen Shot 2020-09-03 at 6.50.00 PM|329x499]

Once this is all done, just use the rotate and array functions to create the rest of the indentations. Keep them aligned with the hidden geometry to ensure a good outcome.

Use my instructions above to make the tower. With no solid tools: you’ll want to make groups, move them, explode them, intersect them, delete the unwanted geometry and regroup them. It’s a little labor intensive but can be done in the Make or Web version as described here. Happy modeling!!


thanks so much guys

Now I encounter this thing: if I try to replicate my dome more than 12 times it does this and so I can’t erase the cap that it forms. I tried putting more segments on my cylinder, but didn´t work. Any ideas??

What size is your cylinder? The domes and cylinder intersection will make lots of small edges, which SU may merge if edge endpoints are too close together.

You may need to make it into a component, then scale up a copy x100 or x1000 and Zoom Extents…

Work on the copy, for example use dimensions in metres instead of mm. When done, delete the large copy, and Zoom Extents again.

For further information search the forum for “the Dave method”.

Upload your .skp file to the forum to get further help.

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thank you, I think that’s the issue. the cilinder is in mm and is about 7cm diameter. is set to be 3d printed.

I think you missed the point of my gifs. The trick is to make the dent fit the faces. If you turn on hidden geometry in your model you will see that the vertical lines are not fitting your domes.
If you want to do it that way you need the dome to extend through the faces and then intersect and remove all the extraneous parts.
Or, as I show above, create a circle with the correct number of facets to fit your design.
You need to remember that everything is made up of flat faces and edges, and when circular those faces change angle, so a dome cut to one set of facets won’t fit another set that aren’t correctly aligned.

You can see in this gif how the edges of the cut dome only touch the face of the ring correctly at specific points because of how the cylinder is constructed. The rest of the time they either miss or extend through.