I’ve tried all my creative abilities as a newbie to figure this out, but seems like I’m unable… And I’ve searched for any possible wording. Have tried Luban and today Cura.
I want to use one model to cut out parts of another model. E.g. inprint a letter in a square, like this:
Is it possible in Luban or do I have to use another program?
Thanks in advance.
Welcome to the wider world of making your own objects.
There’s a lot of learning you can do, and great resources on the Internet. I’ll try and point you at some.
First, the basics: Luban and Cura are slicers - meaning they take a 3D object in the form of an STL file and output gcode the machine runs.
An STL file, which is short for Standard Tessellation Language, is an object represented by triangles, also called a mesh, like so:
To directly edit such a file, use software such as TinkerCAD
For more information, you can start by checking out:
They have articles regarding exactly what you’re after here: https://all3dp.com/1/7-free-stl-editors-edit-repair-stl-files/
They have an article about making new models from scratch here: https://all3dp.com/1/best-free-3d-modeling-software-for-beginners/
Edited because @Atom’s TinkerCAD suggestion is great, I keep forgetting about it.
@brent113 is correct, however If your just starting out and want to do minor edits to existing .stl files or even make your own, try tinkercad. Its free, browser based (no install) and can get you started with the idea of manipulating models. If you want to do more then you will need more complex programs like meshmixer, fusion 360, freecad, blender, etc.
For that you want Tinkercad. The demo basically teaches you how to do that.
The one downside to Tinkercad is there aren’t a lot of font choices.
I do use both Tinkercad and Fusion 360.
Sometimes I use them together.
Tinkercad is great for creating simple items. (not that you can’t make some incredibly complex ones still).
Fusion is super powerful but the learning curve is steep.
For CNC, though you need to take a 3D item and tell the router what to do.
So I may create the item in Tinkercad (CAD - computer aided drafting), then export as an STL and then do what’s called CAM (computer aided machining).
For 3D printing you just export your object as an STL and then use Cura or Luban to slice it (as @Atom said)
-S
The specific example of in-printing the X is pretty easy to create a model in tinker cad. It lets you create objects as positive or negative objects, then merge them. So I’d create a positive square, and make it as deep as the X in the square. Then import the block, and make it a negative object. Move them so the positive square overlaps the X, then join the objects together. You should be left with just the X that didn’t exist in the negative model.
Getting that to print onto an existing object is trickier. Most prints start on the build plate for obvious reasons. I haven’t found any way in Luban to start the print in mid air that doesn’t involve manually editing the GCode. If anybody knows other slicers that support this ability, that would make things easier.
Even if you do get it working, your nozzle won’t fit inside that X to start printing at the bottom. You’d want to modify the original object so that the X is only one or two layers deep, otherwise the hot end will hit and melt the object that you’re trying to overprint.
Simplify3D supports this. When slicing you can control where on the model it starts and stops slicing, as specified in Z height from the buildplate. For example, in the event of a print failure that you would like to recover you can reslice so that it begins at 50mm.
I don’t think he’s asking to print something on something else.
He just want’s to modify an existing stl.
Tinkercad works great for that and is super simple to do.
The only problem is it has a size limit on the stl it will import. So more detailed objects with a lot of faces can cause problems.
You can take any object and make it positive or negative.
It also has letters included as objects (although not a lot of font choices) and a wide variety of other objects.
-S
re-reading, I think you’re right, and I misunderstood. But I learned something new about Simplyfy3D in the process. 
Thanks everybody, getting to understand a little more how to “make something wonderful” with my new SnapMaker 2.0 350!!