How to delete a part of an object?

Question

Opened this file in Blender.

Trying to delete a bottom part with a Knife, then with a Plane, but nothing works. For example I've tried hints from here, from this tutorial

When I used a Plane to cutt off a bottom, after the fourth step nothing happened (tried to press Apply button as well):

• this is the result of the 4th step.

Answer 1

Are you trying to cut it flat on the bottom?

A few ways that I can think of are:

--Go to front orthographic view, go to wireframe mode, and in edit mode, press B(box select) and select how much you want to cut off from the mesh.

--Create a cube (not a plane) that covers what you want to cut off, and on the crater surface add the boolean modifier and instead of intersect, change it to difference, and set the Object to the cube.

example of boolean modifier:

--Create a line and use knife project, and enable "cut through", this will cut this line through the mesh from the angle that you are looking at it.

-- You could also use the bisect option in the tools tab, which will cut a line all the way around your object. Just click at the start point, and drag it out.

--To ensure a flat bottom, go to front orthographic, wireframe, select the bottom part, and hit "S" (scale), "Z" (z axis), and "0"

Bisect tool:

Hope one of these ways works, and good luck!