Hi Steve, usually to cut a groove you will probably want to create a sweep something like this:



Then once you have that tubular pipe running along the object, you can use boolean difference to cut the main body with it, leaving a groove:



Is that the kind of thing you want?

Let me know if you would like some more details on this method, or if you are having problems applying it to a particular model (if so, please post the model if possible it helps to be able to examine it).

- Michael