How to extrude inwards on corners

Hello! What i need is this:

Let’s say i have a clean corner and i need to cut a sort of a hole into it like that. How do i do this?

If i just extrude from one side, it would leave me with overlapping faces and weird disconnected topology. So how to do this?

I tried to find an answer in the internet, but it looks like if nobody else has this problem, even though to me it looks like a very common operation and therefore a huge obstacle.

There’s got to be a way to do it, maybe a tool for it, right?

If it’s an edge, you could always do a bevel with a profile of 0

cmd b to bevel an edge, then once you commit you can set it, like this:

aside from that, you can also create a cut with the boolean modifier

there’s an add-on called bool-tool that makes it really quick and easy, too

if that’s not enough, you could always just cut the thing in with the knife.

In all honesty, bool-tool subtract is best for this, unless you specifically want it to match the upper polygon. In that case, I’d just cut out the polys at the sides and manually create the faces.

As far as I know, there’s no instant press-a-button-get-a-cavity feature (wish there was), but if you want to stick to straight up, non-booled geometry, this is what I’d do:

Make your cuts, then selected the faces where you want your cavity to be, and remove them.

Next, turn on vertex snapping, select any one of your outer edges, and extrude them out along the appropriate axis, hovering your mouse over one of the vertex points you want your new edge to be flush with. You’ll see a little yellow circle appear over the vertex, showing you it’s snapping to it.

The rest is easy. Select two edges where you want a face to be, and hit the F key to fill in that space.

Then do this twice more for your remaining empty spaces. Et voila, you’ve got yourself a nice cavity.

You might want to have a look at this add-on, its still a bit buggy in 2.8 but worth a look.

From this thread Destructive Extrude [BETA]

Alternately, there’s also the F2 addon. Supposedly, it allows you to make even quads from just three vertices. It’d make situations like this child’s play, just a series of fill commands.

…but I’ve never been able to get it to work, so I can’t exactly recommend it.