chopping the corners off a block

[rols]

I tried hole as well, indeed it gives me internal faces, ie a hollow into the box which wasn't what I wanted. Intrude does the same, gets rid of the block but leaves the remainder empty and not closed.

Either I'll continue starting small and extruding out the piece I want, which works perfectly but requires me to think backwards (start small, add on instead of start full and remove). Or else I found I can loop cut the whole object into separate objects, each of which is a long thin block. I can then shorten the ones I want to make gaps in the edge, and then join them all back up together again. That's pretty long-winded but works, I suspect it also means there's a basic concept I haven't grasped.