Re:Question about rafters for a punchbag
lol, sounds about right
ok, so if you get something thin, but flexible-ish, and push it up through the hole parallel with the batten, it will stop when it gets to a joist. at most they will be 600mm centres, so it cant be more than that in either direction! use the stick so you know how far away the joist is and where to make the next hole!