WHen it comes to grounding machinery this can be the most important aspect in keeping your machines up and running. I am no expert in this field and it is an extremely highly debated subject. So, here are some good articles to help understand machine grounding principles and concerns. Most control manufacturers recommend ground rods. All of the electrical noise problems that I have personally encountered, have all been grounded to the building ground. By using a grounding rod for all of them I was able to eliminate the problems. From some of the articles below it does seem that using grounding rods will cause more damage to machine tools during lightning strikes, which I have seen happen many times. Always check with the machine tool builder for their recommendations. Some builders and control manufacturers will not warranty components if it is not grounded to their spec.
Here are some great links to get a better understanding of this highly debated subject on machine grounding.