Part 11 (1/2)

Sc.r.a.ping tools are of such nature that they can only abrade or smooth surfaces.

[Ill.u.s.tration: Fig. 142. Auger-Bit-File.]

[Ill.u.s.tration: Fig. 143. Single-Cut Blunt, Flat, b.a.s.t.a.r.d File.]

[Ill.u.s.tration: Fig. 144. Three-Square Single-Cut File.]

[Ill.u.s.tration: Fig. 145. Open Cut, Taper, Half-Round File.]

[Ill.u.s.tration: Fig. 146. Double-Cut File.]

[Ill.u.s.tration: Fig. 147. Cabinet Wood-Rasp.]

[Ill.u.s.tration: Fig. 148. File-Card.]

_Files._ Figs. 142-146, are formed with a series of cutting edges or teeth. These teeth are cut when the metal is soft and cold and then the tool is hardened. There are in use at least three thousand varieties of files, each of which is adapted to its particular purpose. Lengths are measured from point to heel exclusive of the tang. They are cla.s.sified: (1) according to their outlines into blunt, (i. e., having a uniform cross section thruout), and taper; (2) according to the shape of their cross-section, into flat, square, three-square or triangular, knife, round or rat-tail, half-round, etc.; (3) according to the manner of their serrations, into single cut or ”float” (having single, unbroken, parallel, chisel cuts across the surface), double-cut, (having two sets of chisel cuts crossing each other obliquely,) open cut, (having series of parallel cuts, slightly staggered,) and safe edge, (or side,) having one or more uncut surfaces; and (4) according to the fineness of the cut, as rough, b.a.s.t.a.r.d, second cut, smooth, and dead smooth. The ”mill file,” a very common form, is a flat, tapered, single-cut file.

[Ill.u.s.tration: Fig. 149. a. Diagram of a Rasp Tooth. b. Cross-Section of a Single-Cut File.]

_Rasps_, Fig. 147, differ from files in that instead of having cutting teeth made by lines, coa.r.s.e projections are made by making indentations with a triangular point when the iron is soft. The difference between files and rasps is clearly shown in Fig. 149.

It is a good rule that files and rasps are to be used on wood only as a last resort, when no cutting tool will serve. Great care must be taken to file flat, not letting the tool rock. It is better to file only on the forward stroke, for that is the way the teeth are made to cut, and a flatter surface is more likely to be obtained.

Both files and rasps can be cleaned with a _file-card_, Fig. 148. They are sometimes sharpened with a sandblast, but ordinarily when dull are discarded.

[Ill.u.s.tration: Fig. 150. Molding-Sc.r.a.pers.]

_Sc.r.a.pers_ are thin, flat pieces of steel. They may be rectangular, or some of the edges may be curved. For sc.r.a.ping hollow surfaces curved sc.r.a.pers of various shapes are necessary. Convenient shapes are shown in Fig. 150. The cutting power of sc.r.a.pers depends upon the delicate burr or feather along their edges. When properly sharpened they take off not dust but fine shavings. Sc.r.a.pers are particularly useful in smoothing cross-grained pieces of wood, and in cleaning off glue, old varnish, etc.

There are various devices for holding sc.r.a.pers in frames or handles, such as the sc.r.a.per-plane, Fig. 111, p. 79, the veneer-sc.r.a.per, and box-sc.r.a.pers. The _veneer-sc.r.a.per_, Fig. 151, has the advantage that the blade may be sprung to a slight curve by a thumb-screw in the middle of the back, just as an ordinary sc.r.a.per is when held in the hands.

In use, Fig. 152, the sc.r.a.per may be either pushed or pulled. When pushed, the sc.r.a.per is held firmly in both hands, the fingers on the forward and the thumbs on the back side. It is tilted forward, away from the operator, far enough so that it will not chatter and is bowed back slightly, by pressure of the thumbs, so that there is no risk of the corners digging in. When pulled the position is reversed.

[Ill.u.s.tration: Fig. 151. Using a Veneer-Sc.r.a.per.]

One method of sharpening the sc.r.a.per is as follows: the sc.r.a.per is first brought to the desired shape, straight or curved. This may be done either by grinding on the grindstone or by filing with a smooth, flat file, the sc.r.a.per, while held in a vise. The edge is then carefully draw-filed, i. e., the file, a smooth one, is held (one hand at each end) directly at right angles to the edge of the sc.r.a.per, Fig.

153, and moved sidewise from end to end of the sc.r.a.per, until the edge is quite square with the sides. Then the sc.r.a.per is laid flat on the oilstone and rubbed, first on one side and then on the other till the sides are bright and smooth along the edge, Fig. 154. Then it is set on edge on the stone and rubbed till there are two sharp square corners all along the edge, Fig. 155. Then it is put in the vise again and by means of a burnisher, or sc.r.a.per steel, both of these corners are carefully turned or bent over so as to form a fine burr. This is done by tipping the sc.r.a.per steel at a slight angle with the edge and rubbing it firmly along the sharp corner, Fig. 156.

[Ill.u.s.tration: Fig. 152. Using a Cabinet-Sc.r.a.per.]

To resharpen the sc.r.a.per it is not necessary to file it afresh every time, but only to flatten out the edges and turn them again with slightly more bevel. Instead of using the oilstone an easier, tho less perfect, way to flatten out the burr on the edges is to lay the sc.r.a.per flat on the bench near the edge. The sc.r.a.per steel is then pa.s.sed rapidly to and fro on the flat side of the sc.r.a.per, Fig. 157.

After that the edge should be turned as before.

[Ill.u.s.tration: Fig. 153. Sharpening a Cabinet-Sc.r.a.per: 1st Step, Drawfiling.]

_Sandpaper._ The ”sand” is crushed quartz and is very hard and sharp.

Other materials on paper or cloth are also used, as carborundum, emery, and so on. Sandpaper comes in various grades of coa.r.s.eness from No. 00 (the finest) to No. 3, indicated on the back of each sheet. For ordinary purposes No. 00 and No. 1 are sufficient. Sandpaper sheets may readily be torn by placing the sanded side down, one-half of the sheet projecting over the square edge of the bench. With a quick downward motion the projecting portion easily parts. Or it may be torn straight by laying the sandpaper on a bench, sand side down, holding the teeth of a back-saw along the line to be torn. In this case, the smooth surface of the sandpaper would be against the saw.

[Ill.u.s.tration: Fig. 154. Sharpening a Cabinet-Sc.r.a.per: 2nd Step, Whetting.]