Cabinet-rasps are very coarse files but with single pocket-shaped teeth (Figure 66A) instead of the diagonal serrations raised by the stabbing tool in file-making; they are used before the file for the preliminary rapid abrasion of the wood in shaped work. The usual sections are half round (horse-rasps are flat), with one flat side and relatively thin edges, but their use has largely been supplanted by the range of familiar surform tools—flat, half-round and round file, etc.—in which the chisel-type teeth are raised and perforated in a length of spring steel tensioned in file-shaped or planer-type holders. The perforations allow the sawdust to escape without clogging the work, and the cutting action is therefore very rapid, requiring care in handling, otherwise the form of the work is soon lost. Files are either single cut (6 6B) or double cut (66c), the former generally used for the softer materials, although steel cutting edges are usually filed with the single cut, which gives more of a true cutting rather than scratching action. They are also made in a range of cuts, rough or coarse, middle, common or bastard, second, smooth, dead smooth and double dead smooth. Probably the best type for wood is the bastard double cut, which cuts with a rasping action, and a compound movement should be used, combining a forward push with a slight rocking action which will level the inequalities left by other tools. Files for saw-sharpening are the mill saw-file for circular saws, with rounded edges for forming the gullets, and three-corner saw-files for handsaws. Band-saws require a special band-saw taper-file with more pronounced round to the edges, otherwise the acute gullet formed by the sharper edge of the ordinary taper saw-file is very liable to start small cracks in the band-saw. Needle-files are
66 Files A
66 Files A
very useful for sharpening small tools, bits, etc., and the dead smooth file for coaxing a fine finish to intricate wood edges which the scraper or sanding block cannot reach.
All files should be treated with respect and not thrown into a box with other tools. Woodworking files can be cleaned with wire file card, or if the teeth are heavily choked with resinous sawdust, gently heated sufficient only to scorch the dust, which can then be brushed out of the serrations. Files used for soft brass or aluminium alloy should be rubbed over with french chalk which helps to prevent clogging. It is not generally realized that a softish brass can blunt the teeth of a file quicker than hard steel, and render it useless for other work. Worn-out mill saw- and flat-files need not be thrown away, for the steel is usually very high quality with high carbon content and carefully hardened. Excellent tools, including chisels and scrapers for lathe turning, can be made from them by careful grinding.
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