In addition to supporting your lathe tools the top edge of a tool rest must be nick and dent free. Unfortunately, some tool rests are manufactured from relatively soft metals and nick and scratch quite easily. And, lathe tools are often made of steel harder than the rest itself.
Run a finger along the top edge of your tool rest to feel for imperfections. Small indentations in the tool rest can make it difficult to smoothly slide a turning tool along its top edge, resulting in unwanted changes in the cut being made to the turning. To maintain the top edge of a tool rest, use a fine machinist�s file for the initial smoothing. Using long, smooth strokes, file from one end of the rest to the other. Check the edge with a quality straightedge to ensure you�re not removing more stock from the center of the rest than the ends. With a clean cloth or paper towel wipe the tool rest to remove any residue from filing.
Once the dents and nicks have been filed smooth, wrap a piece of 220-grit paper around a block of wood and use the same long smooth strokes to further smooth the surface. Finally, rub a light coat of wax on the tool rest top edge. The wax not only helps tools slide smoothly along the edge when making cuts, but also helps seal and protect the edge. The wax will wear off, so recoat frequently.