Grinding And Whetting Turning Tools
The skew chisel is sharpened equally on both sides On this tool the cutting edge should form an angle of about 20° with one of the edges. The skew is used in cutting both to the right and to the left, and therefore, must be beveled on both sides. The length of the bevel should equal about twice the thickness of the chisel at the point where it is sharpened. In grinding the bevel, the chisel must be held so that the cutting edge will be parallel to the axis of the emery wheel. The wheel should be about 6" in diameter as this will leave the bevel slightly hollow ground. Cool the chisel in water occasionally when using a dry emery. Otherwise the wheel will burn the chisel, taking out the temper; the metal will be soft and the edge will not stand up. Care should be exercised that the same bevel is kept so that it will be uniformly hollow ground. The rough edge left by the emery wheel should be whetted off with a slip stone by holding the chisel on the flat side of the stone so that the toe and heel of the bevel are equally in contact with it. Rub first on one side and then on the other. The wire edge is thus worn off quickly as there is no metal to be worn away in the middle of the bevels. The chisel is sharp when the edge, which may be tested by drawing it over the thumb nail, is smooth and will take hold evenly along its entire length. If any wire edge remains it should be whetted again.
Fig. 2. - Lathe Tools
The gouge used in wood turning is beveled on the outside and is ground so that the nose is approximately semi-circular in shape. The tool is a combination of the round nose chisel and the ordinary gouge. The bevel should extend well around to the ends so that the cutting edge extends to each side. This is necessary to avoid the abrupt corners which would be present if the nose were left straight across as in the ordinary wood-working gouge. In making shearing cuts the round nose permits the tool to be rolled to the side to avoid scraping the work. The length of the bevel should be about twice the thickness of the blade at the point where the sharpening begins.
The sharpening of a gouge for turning is rather difficult for the average student. The ordinary gouge which has a square nose may be beveled by merely turning it half way around and back again. In working out the round nose of a gouge for wood turning, it is necessary that the handle be swung from one side to the other while, at the same time, the chisel is revolved to cut the bevel evenly. It is sometimes necessary to allow some pupils to use the side of the emery wheel in sharpening the gouge. This kind of grinding, however, does not leave the tool hollow ground as when the face of the wheel is used.
To complete the sharpening the rough edge is worked smooth on a slip stone, the cross section of which is wedge-shaped and the edges of which are rounded. The toe and heel of the beveled side of the gouge are brought into contact with the flat side of the stone. As the sharpening proceeds the wire edge is worked to the inside of the gouge. The rounded edge of the stone is then placed inside the gouge and is worked back and forth until the rough edge disappears. Great care must be taken not to bevel the inside of the gouge when whetting with the round edges of the stone, as the result will be the same as with an ordinary chisel or plane bit.
The parting tool is sharpened on both sides. This tool differs from the ordinary chisel in that it is between ⅝" and ¾" thick and only about ⅛" wide at the widest point, which is in the center of its entire length. The bevels must meet exactly at the center, or the widest point, and should make an angle of about 50° with each other. If the bevels do not meet at the widest point the tool will not clear, and the sides will rub against the revolving stock; the tool will be burned and will thus lose its temper. The bevel should be hollow ground slightly as then comparatively little metal need be removed when whetting.
The round nose, square nose, spear point, right skew and left skew are scraping tools, used chiefly in pattern work and sometimes in face-plate work. They are sharpened on one side only, and the bevel is about twice the thickness of the chisel at the point where sharpened. These tools should be slightly hollow ground to facilitate the whetting. Scraping tools become dull quite easily as their edges are in contact with the wood almost at right angles. After sharpening, the edges of these tools may be turned with a burnisher or the broad side of a skew chisel in the same manner that the edge of a cabinet scraper is turned though not nearly to so great a degree. This will help to keep the tool sharp for, as the edge wears off, the tool sharpens itself to a certain extent. The chisel is of harder material than a cabinet scraper so that it will not stand a great amount of turning over on the edge. Small pieces will be broken out, unless a flat surface is rubbed against the edge at a more acute angle than was used in the whetting. If a narrow burnisher is used, pieces are more likely to be broken out from the sharp edge and thus make the tool useless.
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