How do you stop a Galah biting?

My Galah Aussie will not stop biting my hands when i try and touch him, he will let me get him out of the cage and he is happy enough to sit on my hand when he is out of the cage, but he will not let me pet him. I have help his beak, told him no, put him back in the cage, and calmly ignored it. but nothing seems to be working, and i really don't want to harm our relationship by negative reactions. he seems to be happy enough when he is out of his cage and being around me ( he is out of his cage between 1-6 hours a day, depending on when i'm working)and he has a lot of chew toys in his cage, so he has things to bite and play with. , though he starts biting me the second i try and touch him or pet him,can anybody help?