One of the most effective tools used to shape and clean steel is the grinding wheel. These high-speed tools are able to rapidly remove large quantities of material but can often leave behind marks on the finished part. Some gouges left by a very coarse grinding wheel are best removed with progressively finer grained stones. However, even the finest stones can leave behind marks that can only properly be removed through the process of polishing.
Things You'll Need
Place the steel part to be polished in the vise in such a way that the steel lies parallel to the vise or ground. This will make it easier to keep the sanding block flat against the part. To remove the grinding marks, the material in the high portions of the grinding marks must be removed to match the low spots without making the low spots deeper.
Wrap the 40-grit sandpaper around the sanding block so the paper is taut and flat. Use long strokes with slow, steady pressure to remove the steel. Make sure the block is square and flat against the steel so the entire surface of the sandpaper is in contact with the steel part. Continue sanding until the surface is uniform in appearance. It should have a dull luster when finished.
Sand the part with progressively finer sandpaper, working from 40-grit down to 320-grit. Once finished with 320-grit sandpaper, the grind marks should be completely removed. If a polished surface is desired use 600-grit sandpaper and water to remove the very fine scratches left by the 320-grit.
Avoid using circular motions since this will leave shapes in the steel that are harder to remove. Instead, use long motions alternating between strokes perpendicular to the steel and parallel for each grit of sandpaper.
The sandpaper can be coarse and slightly scratch the hands. If this is a concern, work gloves can be used to prevent injury.