I`m a beginner woodworking student and the other day we built a bookcase which was sanded after being assembled. I was wondering: isn`t it much better to sand all the parts with all the different grits before assembling? then putting the whole thing together? I found it extremely hard to sand the the bookcase as a whole. I would apprecciate getting help as to when to apply the sand paper and what grits i should use. Thanks.