The dowels need to be 90 degrees to the miter joint. You need a dowel jig to position them exactly in the same spot on both sides of the miter joint, doesn't matter if it's 45 degrees, 30 degrees or any degree in between as long as you stay 90 degrees to that joint they go together fine. Barring that free handing it is next to impossible to get a tight clean joint. The newer way of doing this now days is with a Kreg jig and drilling angled pocket holes and screw the joint together and/or gluing as well. Much easier to do and way more accurate. Additionally plugs can be used to hide the screw holes, so you get the same effect, but even those will still be 90 degrees to the miter joint.
If you must use dowels and you don't have a jig, then your best bet would be to use a horizontal drill press and use a stop block and clamp your pieces to get your holes in the same place on each piece. Dowel jigs and hand drills are much easier...lol...probably why they make them.
Last edited by GoNavy429; 11-25-2013 at 12:19 AM.