What I do gents which I find easier is I drill each piece of metal separate and drill the blank before cutting in half. Using epoxy I glue all parts and then put the tube in the first part of the blank followed by each piece of metal and then the other part of the blank. The tube lines everything up and then I clamp.
I have stopped doing it by gluing everthing first and then drilling afterwards because as you break through each part of the metal the drill will attempt to snatch on the breakthrough and will stress the glued joints causing the whole lot to come apart!!!
I hope this helps and also with epoxy you have time to play before it goes off.
