The cutting edge of a lathe tool should be set right on or just slightly below the centerline of the part being machined. With new lathe tools this is not a problem, because Sherline tool posts are made to hold them at the correct height. Older tools that have been sharpened numerous times may require shimming to bring them up to the correct height.
The Sherline rocker tool post is designed to eliminate the need for shimming. The height of the cutting edge can be changed by simply adjusting the two clamping screws. This inexpensive accessory reduces setup time and also extends the life and the usefulness of your old lathe tools.