The problem I have always struggled with is getting the hole in the right place. Not too far in and not right on the edge.Even swapping the pin holes still didn't work for me.
Was lying in bed last night and had an Ahhhhhhaaaaa moment. Jumped up to write it down, tripping over 2 dogs and waking up DH and the cockatoo on the way!
Today I made a piece of polymer clay to fit into the slot so that when the metal is pushed in, the hole is pierced always the same distance in from the edgeThe spacer can slide out if you need the full depth.
Then I made a small polymer clay 'table' that fits each side of the punch so that what you wish to punch, sits horizontal with the pin.
Cut a centre line on the face of the punch and centre lines on the 'table' to make punching 2 holes opposite each other easier.
Test runs have all worked perfectly.A quick down and dirty solution that I am sure can be improved