The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Coloring Finishing And Painting Wood
Surface Abrasives And Their Use
6. Inspection Before Sandpapering.—Inspection of the surfaces to be sandpapered is an important preliminary which should never be overlooked. If rough spots or planer-marks have been left they should be found and removed before any sanding is attempted. Hand sandpapering will not remove or cover up defects of this kind. It always wastes time and increases the difficulty. Scraping out the unfinished places later on is harder because sandpapering always leaves sand in the pores of the wood, and this sharp grit soon dulls the edge of a scraper-blade. Very frequent sharpenings of the hook on a scraper are necessary, if scraping is attempted after wood has been sandpapered.
Amateur wood-finishers should learn what defects to look for, and should realize that planer-marks and minor blemishes that hardly show on the natural wood are greatly exaggerated on the finished piece, especially, if stain of any kind is used. Bough surfaces practically always expose more cross-sections of the pores or end grain, which, when stained, will show darker than the rest of the surface. This is due to the fact that the end grain of wood is always more porous than the ordinary grain of longitudinal or transverse sections. See Fig. 3.
7. Sandpaper Manufacture.—Sandpapers of the present day are not made from sand and paper. The grit which looks like sand is made from quartz or flint rocks. The red or garnet papers have a grit made from garnet ore. Great hardness and sharpness of edges are important factors in a grit. Natural sand, while hard, has few sharp edges, as all such cutting places are soon worn off and smoothed by rubbing against each other, just as rocks on the mountain sides are smoothed and rounded by glacial action. Sharp grit is made from crushing hard rock and sifting in order to secure particles of uniform size. Various sizes of rock fragments, sometimes called sand, are secured in order that sandpaper of different grades of coarseness and fineness may be manufactured.
The best grades of paper are strong, especially when made from Manila fiber which is sometimes secured from old ropes, and the strength is also increased by a crisscross or uneven arrangement. Papers which are made so that the fibers are not parallel with their lengths in one direction are stronger crosswise and have nearly uniform strength in every direction. Such papers are difficult to tear and, if torn, leave a rough uneven edge. Thicker papers are used when coarser grits are to be applied.
In the manufacture of sandpaper, rolls of paper run through a machine, unwinding and passing along as in a printing press. Hot glue of a good grade is spread evenly over one side of the paper. The sand is then sprinkled to a uniform thickness over the surface, and the excess grit which does not become set in glue finally disappears falling off after the paper turns over a roller.
