I have a home made X Y table from part of a small mill on my bench drill which I use for coordinate drilling.
One problem is a limited quill travel of 50 mm and switching from a centre drill to a twist drill takes up nearly all the travel and moving the drill head loses the datums.
The answer is to make an extension for the centre drill to match the length of my edge finder and the length of the average twist drill. Made two for different sizes rather than a double ended one and rather than use grub screws I have simply used Threadlock which is easily removed with heat.
The bench drill has been modified to enable the head to be lowered on the column to within range of the job in hand.