I wish to utilize an existing concrete post as a support for a wooden end post (slotted), because it is slotted I can't really use a clamping method. So I tried to drill threw it...I've removed 14 of them already so i know the position of the metal bars running threw them. It's just not happening! Tried using 'bits' for the obvious stone, masonry etc. I cannot remove this post as to the position of it and what is around it. Appreciate any ideas/advice.
Try using a very small drillbit first and then enlarging the hole. Posts are constructed using very small aggregate to stop any air getting into the finished compact mix. The stone availabkle for this size of aggregate is usually shingle which is about as gard as it gets. If you can start with a 4mm masonry bit and then work up you should be able to do it. The set in the link below has a 4mm bit in it.