I cut them too thick so only a few came out as crisp crisps. It'd be handy to have a mandolin like this, but with thinner slices :
One suggestion I found was to use the side of a grater, so I'll this next :
Another couple of things - make sure the fat is hot enough, one tip I saw was to put the handle of a wooden spoon into the oil and if bubbles appear it's hot enough. I've got a cooking thermometer but will try this next time
I was thinking of making flavoured crisps, so, when you put the potato slices in water to get rid of the starch I might try adding a beef or chicken stock cube and let them soak overnight.