Thanks for the feedback guys and the links, much appreciated.
I'm pushing to do as much as poss atm as we're due our first in September. I'm sure everything will grind to a halt then.
A couple of hours spent today.
I found this quite stressful due to wanting to achieve perfect dimensions. As it turned out it was bang on in all but one which was out by a mm. Using enough amps generated a ridiculous amount of heat however it's penetrated well.