Thank you everyone for all of your comments, I should have been more clear. This patio will have 6 posts, four of which will be on the existing concrete patio which is prob 4" deep, perhaps more perhaps less. When I went to get a permit I was told the footings had to be a minimum of 12" deep. One of the posters mentioned "why not just put the post on top of the existing patio? That was my original idea too. But the permit guy told me I couldn't do that, and it will prob be safer to have a nice deep footing anyway, I actually plan to dig down 24". My location is Memphis TN, so frost heave is prob not a issue at 12" to 24" deep footings. I have never had to cut concrete and end up with nice edges. All I have is wood working tools and I do not want to use them on the concrete. I like the angle grinder idea and the skill saw idea. With the diamond blade. Get a nice straight line going then start tapping the middle and hope it breaks clean. I think the angle grinder would be easier to get the cuts started right? But then it would not go as deep as the skill saw. With the 4.5" angle grinder how deep could I make the cut? Looks like harbor freight has a 9" 15 amp angle grinder. Has anybody used this one? How deep do you think I could get with that?
-Nic