As part of my 'model' of a concrete apron for the top of a dock I have also created the 'gutter' using the mesh object for the apron (rather than create using single vertice and extrude again) which will be 'dropped' onto the apron creating a 'concrete apron' with a 'concrete gutter' around the edges (see image) below. In doing so I now need to remove part of that 'gutter' and considered using a boolean modifier. However I just can't get it to work. I added a mesh cube (colored red in the image below) with correct dimensions to 'cover' that part of the 'gutter' mesh object I want to remove and tried 'difference' but don't seem to be able to get it to work. Maybe I am using the wrong 'tool'?
if this is what you are looking for:
use this boolean modifier:
don't forget to choose an object - in your uploaded file no object was chosen so Blender cannot execute the boolean modifier.
Also make sure that the cutter is hidden - else you cannot "see" the cut.
And...the boolean modifier is on cube.001 ...you added yours to the wrong object - if i understood you right.