The Technique of FURNITURE MAKING

Sharpening stones Oilstones

For the whetting or honing of ground edges (and all edge tools are supplied ground but not honed) a variety of stones are necessary. They can be either India, carborundum, or the slower cutting Washita, which is an inferior form of Arkansas, while true Arkansas is very scarce and expensive. Both India and carborundum grits are artificial, and therefore their quality is consistent, but Washita is a natural stone and can vary considerably, with an occasional piece almost too hard to cut; the best, however, will give an excellent edge. All these stones are usually bought in the standard size of 8 in (203 mm) by 2 in (50 mm) by 1 in (25 mm) for sharpening chisels, plane-irons, etc., and should be mounted in a wooden box with a lid (Figure 65), or otherwise covered when not in use.

A nail driven into the base of the box and pinched off to leave about 1/16 in (1.5 mm) protruding will prevent the box slipping on the

sharpening-table. For general use three oilstone grits are available—coarse, medium and fine; the coarse is for the rapid restoration of grinding bevels and the medium and fine for general honing, but for occasional use only double­sided combination stones with coarse and fine grits are obtainable. For those who tend to round their bevels over when honing on the oilstone (and the knack of working with the elbow and not the wrist takes time to acquire) a honing-gauge mounted on a ball or roller and set at the correct cutting angle is a useful accessory.

Water stones

Over the past few years a growing number of craftsmen in Britain and the USA have swung over to using inexpensive Japanese water stones. These are only available from specialist tool suppliers and, due to their extreme soft­ness, are unsuitable for the novice or for school use. However, used with care, they cut fast, produce a near perfect edge, and avoid the use of messy oil. This latter is important as it is a basic necessity for the furniture-maker to keep his hands clean and free from grease, or he will spend half his time cleaning off dirty thumb prints.

Even their softness in the hands of a crafts­man is an advantage as they can so easily be trued up by surfacing with a new coarse, but cheap, carborundum stone, thereby ensuring that one is constantly using a perfectly flat stone.

They are available in several grits; the writer manages perfectly with two only: 1200 and 1600.

Strops

An effective strop for fine cutting edges can be made out of a spare piece of cowhide, unmounted for carving tools so that it can be bent to shape, or glued to a wood base rough (undressed) side uppermost for chisels and plane-irons. The leather is dressed with oil and sprinkled with fine carborundum powder. The old school of craftsman always used the palm of his hand as a very effective strop.

RASPS, FILES, ETC.

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 (66B) 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

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.