In the process of making, shaping, and finishing furniture, it is important to have a working knowledge of abrasives, especially when working with complex and compound form (Figure 8.49).
Abrasives are used to cut, etch, grind, sand, and texture material. Abrasives affect the finish quality of a material’s surface and its visual appeal. In working with wood, the function of abrasives and sanding papers is to cut away the wood fibers by the rasping action of various tools and materials.
Following is an outline of techniques to consider when using abrasives and sanding papers.
■ When sanding wood for a lacquer finish, always sand (or scrape) in the direction of the wood grain. Never sand across the grain.
■ In general, start with 80-grit, follow with 120-grit, and sand for finish with 150- grit, depending on how well the lumber
was milled. Do not skip between the Figure 8.49 Valet chair being made at PP M0bler, Copenhagen, 80-grit and 150-grit papers. Denmark. Photography by Jim Postell, 2006.
■ Consider incorporating a V-groove or a quirk joint where two different woods meet. A V-groove is a shallow cut into the face of the grain with an angled or chamfered profile resembling the letter V This will minimize the possibility of the darker wood discoloring the lighter wood in the sanding and finishing process.
■ Apply even pressure when sanding by hand with a sanding block or with power tools. When necessary, use a rubber-backed hand-sanding block. Paper scratches caused by the sides of folded sandpaper are important to avoid.
■ In order to determine where you have already sanded, consider drawing random pencil marks over the area to be sanded. When the pencil marks have been removed in the sanding process, the area has been uniformly sanded.
■ Avoid using steel wool between coats of finishes; it can discolor the wood and agitate the surface. Rather, consider using 320-grit sandpaper or Scotch-Brite™ scuffing pads between coats.
■ In some applications, try scraping the wood in the direction of its grain rather than sanding it. Scrapers, when used properly, can more quickly prepare wood for its final sanding for the finish. The effect is significant. Cabinet scrapers and hook scrapers require careful, regular sharpening using an oilstone.
■ Do not oversand with the finer-grit papers. Oversanding polishes the surface of the wood, preventing the finish from penetrating into the wood or bonding mechanically to it.
■ To dull or make satin a glossy lacquer, polyurethane, or polyacrylic finish, use a Scotch-Brite or similar pad over the finish when it is completely cured.
■ Sandpapers can be used to sand wood finishes, metals, glass, and stone. Open-coat garnet paper is available as a reddish-brown paper and is a good general-quality abrasive for sanding wood by hand. Open-coat aluminum oxide paper is harder than garnet paper and is widely used as the abrasive sheet for power sanders when sanding wood. Closed-coat silicon-carbide paper is generally used for finishing metals. It can be lubricated with water or thinner and is called wet-or-dry paper.