I’ve never used a 3d printer before but want to get one. I have a bit experience in blender but not too much. My question is: How do you model for a 3d print? For example, if I want to print a hollow cylinder, I go into blender, create cylinder and delete the side faces. If I print this, the walls will be pretty thin. Do I have to make them bigger manually? and if I do so (extrude and scale) does my slicer (cura) automatically fill in the solid part?
First off I’ll say that what programs you’d want to use depend on what kind of things you’re wanting to design. If you’re wanting to design something artistic (a sculpture or miniature or model of a space ship or whatever), Blender’s a great choice. If you’re wanting to design something that’s more for mechanical use (a custom wall mount for something, a replacement gear for machinery, a case for a Raspberry Pi, whatever), you’ll probably be better served using a CAD (Computer-Aided Design) program like TinkerCAD, FreeCAD, AutoCAD, or OpenSCAD.
I do a lot of CAD sort of model designs and I personally love OpenSCAD, but it’s made very particularly for programmers. TinkerCAD has a much lower learning curve and is free to use.
I don’t do much artistic model designing for 3d printing. I dabble in Blender too, but mostly just to make minor tweaks to models I found online.
About your cylinder question, you’re right that any slicer would be pretty confused if you gave it a shape like that. To make it work, you’d need a shape that had volume. Not something that’s an infinitely thin surface.
To get a “tube,” you’d have to decide how thick you want the walls and deal with that in whatever program you’re using to make the 3d model. In a CAD program, the way you’d think about this is that you’d add a cylinder and then “subtract” another (concentric) cylinder with a smaller radius. Like, if you wanted a cylinder with an outer diameter of 3cm and a thickness of 2mm, you’d make a 3cm cylinder and “subtract” from that cylinder another cylinder with a diameter of 3 centimeters minus twice 2 millimeters or 2.6 cm. (The second cylinder would also need to be of equal or greater height than the first.)
The result would be an object with volume and with a very specific defined thickness that your slicer would be able to handle nicely.
Where CAD programs let you think in terms of “volumes” of various shapes and combining them in interesting ways, programs like Blender work more in terms of “polygons.” I’m not terribly familiar with Blender, but just off the top of my head, if I were trying to do the same thing in Blender, I might make a cylinder 3cm in diameter, another one 2.6cm in diameter (at the same location with the same height), remove the top and bottom faces of both cylinders, reverse the normals on all faces of the second cylinder, and then manually, one by one, create faces to fill in the “ring” around the top and the “ring” around the bottom.
Does that all make sense?