# Best approach for modeling two interlocked cylinders with different number of vertices (for 3D Printing)?

I'm an absolute noob to 3D modeling but that seemed handy since I bought a 3D printer. I followed a bunch of tutorials already and started my first project: what seemed to be a very simple cylinder for my son's marble run.

the very low resolution of the print is because I found out that making it too round required too much tinkering to get the size absolutely perfect whereas not round fit perfectly.

So it works BUT I'm not happy with the results and would love to stick to that project until I am so I'm sure to have learned a lot. (this is where I need you)

Here are the 3 different approaches that I can imagine:

1. Subtract: My first approach was to use cylinders to subtract one to another until I got to this shape but never got the dimensions right
2. Extrude: Then I tried one (no cap) cylinder + tried to extrude the top narrower part (but failed once again to get the dimensions right)
3. Spin: Finally, using vertices I created the edge exactly where I wanted with the right dimensions: spin + solidify + some beveling on the inside (that's the result you're seeing)

What do you think would be the best approach? knowing that I'd be entirely satisfied only if I manage to keep the top part at the same resolution and the bottom part rounder.

• Hello and welcome. Please use a title that reflects the content of the question. It should be succinct, unique and identifying, and summarize what the issue is so that users can at a glance broadly understand what your post is about before opening it. Use the edit link below your post and avoid any emojis salutations or extraneous text not essential to the question. Remember, your title is the first thing potential visitors will see, and will weight heavily on their decision to open your question, which will directly affect the number of answers you might get. Feb 18, 2022 at 0:25
• @DuarteFarrajotaRamos thanks for editing the title, I tried after reading your comment but couldn't come up with something descriptive enough. I guess "bottle" is close enough :) Feb 21, 2022 at 5:19

## 3 Answers

knowing that I'd be entirely satisfied only if I manage to keep the top part at the same resolution and the bottom part rounder.

The roundness is primarily a function of how many vertices you have. To make it more round, you need more vertices. I'll provide organized steps I'd take, usually along with how I access the operations:

1. Make the top part. Add circle with 16 verts, then enter edit mode (TAB); F face; I inset; E extrude; X -> dissolve face. Inset and extrude to eye or whatever references you have, need to move mouse then confirm:

1. Loop select the outer rim, SHIFT+D duplicate, move in global Z to eye or reference (G Z if orientation set to global, move mouse, confirm.) Subdivide selection (for me, W vertex specials->S subdivide.) SHIFT+S snap cursor to selection. . to set pivot to cursor. "To sphere" operation (from searchbar, SPACE for me) at 1 strength. SHIFT+select the other loop, "bridge edge loops" operation (from searchbar):

1. Loop select the bottom vertices and F face. Leave edit mode and give it a solidify modifier. Tune the thickness of the solidify modifier to eye or reference:

Optionally, or depending on exporting/printing software, apply the solidify modifier. Optionally, or depending, triangulate the mesh (probably via select all, ctrl t in edit.)

This isn't necessarily how I'd do it for other applications, but topology/normals don't really matter for 3D printing. You can increase the roundness of the bottom part by using more subdivisions during that step (from operator panel, or just by subdividing multiple times in a row.)

• wow, thank you for the very detailed answer. I followed your instructions and it worked, I now have to fully understand each step (still confused by the cursor changes and 'to sphere') Thank you again! Feb 18, 2022 at 8:16

Here is how I would produce this shape.

Start with a cylinder and remove the top face. (Make it hollow)

Select the top loop and E Extrude + S Scale.

And then Extrude upwards.

Now use a Solidify modifier with the Even Thickness option selected. This will maintain thickness on the inside corners.

If you need it to be rounder, you can Crease all of the round loops and use a Subdivision Surface modifier.

Inspired by Nathan's answer! this is my take on my own request:

1. Add > Mesh > Circle (vertices: 12 for the top low-res cylinder, radius 12mm for my project)
2. Edit Mode (Tab), Extrude (E), (z) to follow the z axis, move z=7mm
3. Add > Circle (vertices: 60 for a much rounder cylinder and is a multiple of 12 our number of vertices in the first circle, radius 13.5mm for my project)
4. loop select both circles - with edge-select activated, ALT + Click on the first one, SHIFT + ALT + Click on the second one. ALT + F (Faces) to fill the gap between the two (the 'bridge edge loop' method gave me different and unsatisfying results for the next step)
5. loop select the outer rim, Extrude (E) following Z (z). Move z=34mmm (for my project)
6. back to "object mode" (Tab), select the object, add Modifier > Solidify Thickness = -1.6mm, check 'even thickness', Apply
7. Because it's for 3d printing, it helps not to have a surface that is not supported by anything so it requires a little of beveling on the inside: select one by one the 12 edges (not sure why loop select doesn't work here...) and CTRL+B to bevel. width=2mm

Voila! (printed and it worked)

Thanks a lot for the answers, I learned a lot!

Still not clear for me:

• difference of results between "bridge edge loop" and "faces"
• why I wasn't able to loop select the edge inside my object
• why both beveling thickness and offset are negative