"jim" wrote in message ...


If a thin wall is a problem then it's usually better to first bore the cylinder to an undersize condition and slot the ports using whatever convenient means is available, finally finishing the cylinder bore by holding from the part outside diameter in a collet or some type of full grip vise jaw type of fixturing device.


holes with square sharp corners


Does not exist--the best you can do is to approximate by specifying the max allowable mismatch and corner radii.