You have already done the hard bit, mark X in the middle at the end of blank.
Line the vice up and test the alignment by switching on and touching the drill to test.
If it's not right move the bloody vice until it is init?
Only other thing to do do is put a square against the drill and blank to ensure it drills straight through the blank and not through the X and out the side.
What does it matter about being center of blank? As long as there is enuf meat on it it will find it's own center on the lathe, assuming the lathe kisses.
