Welcome to the forum John,
There are a few things that can cause this problem. Getting the T-Rest height correct is of course very important and can take a little practice. If your graver is sharpened to a very fine tip it can easily cut grooves into the stock if your tool post is too far off center. One thing that may help is to grind a small radius onto your graver as shown in the illustration above. Also when cutting try leaning the back end of the graver toward the head stock and “pull” rather than “push” the graver. For soft materials like brass a higher surface speed is needed for a good finish than that required for harder materials like steel. If using a foot pedal control remember to change the rpm according to diameter of stock you are using. You will need to increase the rpm as the stock diameter gets smaller in order to maintain a reasonable surface speed. After practicing for a while this will all come as second nature to you At first though it takes a bit of concentration to get it right. Sort of like driving a car. Kind of.
Please let us know if this helped John. If not we can cover gravers a bit deeper.
Enjoy!
Bob
