I know, in one object, you select two vertices, press F and you have a new edge.
But what with two objects? I select both, go into edit mode.
Select one vertice from one object and one vertice from the other, press F - and NOTHING HAPPENS.
How can I make this work?
thanks!
you can extrude one vertex and snap the newly created vertex to the destination.
You don’t, generally. If you need two objects to be joined, then use the join function itself.
CTRL + J (both objects selected in object mode)
An edge can only be created between two vertices belonging to the same object. The edge also belongs to that object.
As @Hadriscus said: you don’t make edges between different objects but can extrude from one specific object vertex and snap to anothers specific vertex of another object…
(Selecting both and tab into edit mode just edit both objects on it’s own… for example you can duplicate both vertices but then they are still part of their original object.)
You can use hooks, but i doubt it is a desired and practical and reliable solution.
More spooky than hooky 
And it is hard to parent if the vertex lay on each other.
hooky.blend (96.6 KB)
I am not sure what your final aim is, to be honest, so the best solution may depend.
Do you, perhaps, want to do some wiring, like between poles or buildings? There are “curvy” addons that may do that 
Just to add another solution: join the two objects, connect the vertices, then select the old object1, P - break it out, select the other one, and do the same 
This! @Transcendental , you have an “XY problem”:
The XY problem is asking about your attempted solution rather than your actual problem. This leads to enormous amounts of wasted time and energy, both on the part of people asking for help, and on the part of those providing help.
- User wants to do X.
- User doesn’t know how to do X, but thinks they can fumble their way to a solution if they can just manage to do Y.
- User doesn’t know how to do Y either.
- User asks for help with Y.
- Others try to help user with Y, but are confused because Y seems like a strange problem to want to solve.
- After much interaction and wasted time, it finally becomes clear that the user really wants help with X, and that Y wasn’t even a suitable solution for X.
What are you actually trying to do- that is to say, what are you trying to accomplish by doing this? You can’t do this, but you can almost certainly accomplish whatever it is you want to accomplish a different way
Thanks for all your replies. I see that I have to join two objects to bridge gaps between them. Can I separate them again later? (separating objects into two wasn’t really covered in my course except by cutting it in two with the knife tool)
This is what I am trying to do:
I am trying to build the body of a robot. Imagine a knight’s armor. A chest plate and a plate over hte stomach. So I end up with two separate panels for the upper right side and the lower right side of the body.
But there are gaps between them.
I tried to fill them by connecting vertices.
The problem with joining the two panels: they are not too well done (me being a beginner) and it looks like my robot fell off the assembly line and serious dented his looks. I will have to smoothen it out later and if the panels are joined this might be more difficult.
Third solution: I leave the panels loose, like shields and create another body underneath.
Looks like I one has to do these modeling exercises again and again - just as when you learn the piano you have to play the same passages over a hundred times sometimes until you can’t hear it any more.
I also feel that one has to connect one’s way to think with the Blender logic. Just following tutorials - not sure if this leads somewhere.
Are there many ways to build a model and you just have to try a hundred times or is there ONE was to do it right?
At the moment I get the feel there are many ways in Blender, that it is as flexible as it is complex - am I getting the right impression here or am I wrong?
You are correct, there’s many different ways to do something in Blender, especially when it comes to modelling.
This seems like the best idea, at a quick glance- this will allow your robot to be articulated without deforming the panels. But without a closer look at your project, it’s hard to say exactly what will work here
At the moment it’s too ugly to be shown in public but once it has at least a hint of looking interesting I’ll post a project photo.
At that time I’ll know more to ask more detailed questions.
For now, it’s been great to have a confirmation of a first strategy.
The course I am doing has a robot, drawings and all to recreate. But the robot wasn’t my type so I’ll create my own. More difficult but as there are many ways to do things it will, in the end, be more fruitful to create the kind of models that interest me most.
Well, if you really want to extrude vertices from a mesh towards the other you can open both meshes in edit mode and use snap to extrude the vertices of the one you want to modify towards the vertices of the other object. This way you can use both meshes without joining them.
Here I have 2 different Suzannes and I extruded one vertex from one to another in edit mode without joining them:
You just need to select both meshes at once and press tab. Just don’t forget wich object you are working on.
Lol, it seems that I’m only repeating what people have said before. Anyway, that’s what you should do.
I’m really glad so many people are willing to help today.
I actually had a problem related to this I couldn’t figure out the solution for. Maybe someone knows the answer to it:
how to get smooth normal interpolation between overlapping edges of two objects?
You have flipped normals. Turn your Face Orientation on:
Is it late in the day again? 
Don’t be too hard on yourself, easily 65% of the problems posted on this site can be fixed by checking Face Orientation 
Checking-face-orientation is the blender version of the reconfigure-deflector-shield solution for 80% of the problems in some known sci-fi series.
(The other one might by something like switch object/edit mode… )
Thanks. But in my case I can’t extrude anything.
I have both objects selected, in edit mode in Vertice mode, SNAP is on.
But I can’t extrude.
Even with only one object selected and in edit mode extrude suddenly doesn’t work.
This is really difficult because I often can’t even get the tools to work at all and I don’t know what I’m doing wrong - just like in this case: I can’t extrude anything.
The problem are also those courses. They let you just follow someone doing something but those tutors never tell you the logic behind the tools: under which conditions they work and when those conditions are not met they don’t work.
I can select the outline of each of the panels and extrude but I can’t extrude a single vertex.
too late for the party here, but yeah basically what everyone said earlier is your solution 
