Knife edge

“ But since the steel which we use is limited in its hardness and its power of resisting crushing and 79bending influences, the blades of our knives must have a certain strength or thickness, depending upon the character of the material to be cut. For very hard substances the knife must be stout and the edge ground to a comparatively obtuse angle; for moderately soft substances, such as wood, the angle may be more acute, while for very soft tissues the thinnest blade and the sharpest edge are most suitable. ”

“ The right-hand knife must be adjusted so that its edge is exactly parallel with the left-hand knife in order to make the slug of equal thickness throughout its entire length. The faces of the two knives separate slightly toward the front of the machine, which allows the slug to pass freely forward from the cutting edges. The right-hand knife must be shaped so there is a cutting edge of about 1/64 of an inch on the side that stands next to the slug. ”

“ I have seen flint knives in outline very like Fig. 240 in the museums at Cracow, Moscow, and Kiev. Some are highly polished by friction and may have served as sickles.
It is difficult to assign any definite use to the British form of knife, but as the curvature is evidently intentional, and as probably it was more difficult to chip out such curved blades than it would have been to make them straight, there must have been some advantage resulting from the form. As both edges of the blade are sharp, it is hard to say whether the convex or concave edge was the principal object. ”

“ While it is not necessary that the back of the knife and the cutting edge should be parallel to each other, it is absolutely necessary that they be in the same plane, or, as mechanics say,—“out of wind.” If this condition be not observed, the blade will rock on the microtome table as it passes over it, and irregularity in thickness of section will result. ”

“ The plough must be held firm in the groove or guides of the press, to prevent the knife jumping or cutting the edges uneven; and, should the knife be found to run up or down, the defect must be remedied by removing some of the paper or boards placed under the knife where it is fastened to the plough. If there should be none required to bring the knife even with the plough, then a piece must be placed on whichever side of the bolt the defect may require. The head being cut, the same operation is repeated for the tail.
Much precaution is necessary in cutting the fore-edge. ”

“ Therefore wherever a knife with a flat side is used, no attempt should ever be made to grind this flat side on the hone. Such an attempt will almost always result in an edge so irregular that it will be almost impossible to cut a good section with it. But if the under side of the knife be left truly flat, we will have the very best tool that can be had for use with the microtome. ”

“ The cutting edge of the blade is beveled on one face only. This knife represents the general shape of knives of this sort, but is rather smaller than most of them. I have seen some knives with blades fully 5 or 6 inches long and deep in proportion. The handle is almost always of walrus ivory and of the shape figured. I do not remember ever seeing an úlu blade secured otherwise than by fitting it tightly into a narrow slit in the handle, except in one case, when the handle was part of the original handle of the saw of which the knife was made, left still riveted on. ”

“ It is very important for safety that the fingers of the left hand push downward only to maintain an even pressure on the knife blade over the stone. If the left hand pushes laterally with the sharpening stroke, and the knife catches on an irregularity, then the fingers will slip off the edge and can be cut severely by the freed knife blade. With a sweeping motion toward the right of the stone, draw the knife completely across the stone, against the cutting edge of the blade. ”

“ Hone the knife only on the bevel. To remove the wire edge burrs along the edge lay the hone flat on the face and rub gently so as not to round over the edge.
A knife will sometimes cut better after it has been ground the first time. A polished knife will give a better surface to the cut. The cutting of the same kind of stock will often vary with different makes of knives. An oily rag tied to a stick kept handy and passed along the bevel of the knife before cutting hard stock will improve the cut. A blunt bevel is preferred for hard stock; a long, thin bevel for soft stock. ”

“ Since the hole in which the material to be cut is imbedded, is always circular, and since the blade is generally pressed forcibly against the table of the microtome, it is obvious that if the edge of the knife be curved it will sink into the hole to a greater or less depth according as it is further from the centre of the hole or nearer to it. ”

“ In sharpening a knife-blade on an oilstone care should be taken to keep the blade nearly flat on the stone in order to get a thin, sharp edge. The knife should be sharpened first on one side and then on the other, until the desired edge is obtained. ”

“ When you get the right edge on your knife often you can use it the whole day without resharpening, or at most with simply a stropping on a piece of wood or leather. But improper use of the knife, or the least knick, will spoil the edge and sometimes it will be quite difficult to get it back. ”

“ The two-beveled edge is an advantage to the worker in enabling him to cut into the wood at any angle, but it is a disadvantage in that it is incapable of making flat surfaces. The knife is particularly valuable in woodwork for scoring and for certain emergencies. The sloyd knife, Fig. 84, is a tool likely to be misused in the hands of small children, but when sharp and in strong hands, has many valuable uses. A convenient size has a 21⁄2 inch blade. When grinding and whetting a knife, the fact that both sides are beveled alike should be kept in mind. ”

“ Much may be learned on this point from careful inspection of the edge, and trial on a piece of horn, such as an old razor handle. When drawn over a clean piece of horn once or twice the edge of a soft knife is completely dulled; if well-tempered it should scarcely lose its keenness. Again, when laid flat on the thumb nail and pressed, the edge ought to bend up without breaking or crumbling, and at once, when the pressure is removed, resume its original shape. The extent to which extreme hardness and durability, or toughness, may be combined, is well shown in the famous Toledo sword-blades. ”

“ When a knife or chisel is pressed into a piece of wood at right angles to the grain, and at some distance from the end of the wood, as in Fig. 60, a continuous cutting action is prevented, because soon the blade cannot force apart the sides of the cut made by the advancing edge, and the knife is brought to rest. ”

“ A very serviceable knife with excellent cutting qualities can be made easily from a discarded hack-saw blade. The dimensions given in the sketch make a knife of convenient size. The saw teeth are ground off on an emery wheel or grindstone to a smooth edge parallel with the back edge. For the handle, take two pieces of hard wood, dressing one surface of each piece, and cut a groove as wide and thick as the saw blade. Place the blade in the groove and glue the two dressed sides of the wood together. ”

“ A word about the care of carving knives: a fine steel knife should not come in contact with intense heat, because it destroys its temper, and therefore impairs its cutting qualities. Table carving knives should not be used in the kitchen, either around the stove, or for cutting bread, meats, vegetables, etc.; a fine whetstone should be kept for sharpening, and the knife cleaned carefully to avoid dulling its edge, all of which is quite essential to successful carving. ”

“ Care of Table-Knives.—Be careful to keep a good edge to your knives, and do your utmost to preserve them from notches, especially the carving-knife, otherwise a hot joint may get cold while the knife has to be sent from table to be sharpened. A keen edge may be given by cleaning alone, if care be taken, in passing the knife from you, not to let the edge lean on the board, but, in drawing it towards you, to lean with a little pressure on the edge. ”

“ Inside bevel gouges need to be ground on a carborundum or other revolving stone having a round edge. The outfit of the agacite grinder, (Fig. 224, p. 120) , contains one of these stones. The whetting, of course, is the reverse of that on the outside bevel gouge.
Fig. 83. Whetting a Gouge.
Fig. 84. Sloyd Knife.
The knife differs from the chisel in two respects, (1) the edge is along the side instead of the end, and (2) it has a two-beveled edge. Knives are sometimes made with one side flat for certain kinds of paring work, but these are uncommon. ”

“ The steel is so poor it won't hold a cutting edge for any time at all, and the knife has a treacherous habit of closing up on your fingers. I will give you a good Swedish whittling knife like mine, and we will start by putting a good cutting edge on it. ”

“ The workman then takes a strip in his left hand, and, with his thumb on the back and his forefinger on the edge, draws the strips up and down against the knife blade until the soft pithy parts are cut away, and what remains has become fine enough for the next process. ”

“ An example more pear-shaped in outline and ground half-way round the edge, found near Whitby, has been figured. [88] I have a fine one (4 inches) more rhomboidal from Swaffham Fen, Cambridge, and another smaller from Burwell. From the latter place I have an oval knife made from a broad external flake (23/4 inches) ground along one side, and a thick one also of oval form from Icklingham.
Fig. 259.—Harome, Yorkshire. 1/2
In all the specimens with the circular edge sharpened by grinding, the flat side has been purposely made blunt, as if for being held in the hand. ”

“ It makes a clean cut without crushing the edge of the paper. The handle is said to fit the hand
Fig. 58. Paperhanger's Wheel Knife.
perfectly. Fig. 57 shows the position of the wheel knife in the hand when in use. The wheel knife shown in Fig. 58 has a short bevel, off-set steel bracket and maple handle.
Fig. 59. Combination Casing and Corner Knife.
It may be used on any depth straight edge, as it works on a long axle.
Fig. 59 shows a combination casing and corner knife. It has a cutter with a short bevel, serrated edge. It is
Fig. ”

“ Section knives, during the process of sharpening, are subjected to three distinct processes: 1, Grinding; 2, Honing; 3, Stropping.
Grinding is one of the most important, though it is probable that it will rarely be undertaken by the microscopist himself. More knives and razors are spoiled in grinding than in any other way. We have now in our possession an excellent knife, which in an evil hour we entrusted to a New York cutler, and received it back utterly ruined, the temper being entirely taken out of the blades! ”

“ Some spent all their money for knives owning as high as five or six at one time. Their interest centres in the number and sharpness of the blades. Each boy's knife must be sharper than those of others, and comparison of knives with respect to sharpness is common. The blades are tested by cutting into hard material, by seeing which can cut the largest shavings or chips from wood, or by trying to cut paper or a hair. ”

“ Study carefully the knife. No matter how carefully the machine is built, an imperfect knife cannot cut right. Most knives are imperfect in spite of the rigorous specifications given them by makers. They vary in thickness, straightness, concave, bevel, flatness, temper, and quality of steel; and also in the character of their sharpening and honing, which varies with the fineness or coarseness of the grinding wheel and stone. These variations need only be a few thousandths of an inch to cause trouble. ”

“ The last operation to which the knife is subjected is that of stropping, and as the blade should be stropped after every section, it becomes important that our tools should be good and that we should know how to use them. By having two or three knives we can always avoid grinding and honing the blades ourselves, for it is then easy to hire the work done, and half a dozen knives will last a careful worker a long time with merely the aid of a good strop. ”

“ Descended from his flint knife is the abounding variety of steel cutting tools all the way from the razor, concave on both sides, to the axe, doubly convex. As the arts have become more specialized, as artificial power has been introduced, the contrasts of the form of one tool with another have grown more and more striking. The bar which slices metal is stout of build, and rectangular in section, while a lancet is little wider or thicker than a [90] blade of grass. The knives which divide leather, rubber, and rope, differ much from one another ”

“ The knives, both those used for domestic purposes and those employed in works of labour, are of flint, two edged and with a broad blade, and frequently have handles hollowed out of the stone itself.
Not unfrequently these handles are adorned with regular ornaments; at other times, they are less carefully formed, as if they had been destined to be enveloped or inserted in wood. These knives are usually from three to twelve inches in length. They are scarcely ever polished, probably because the edge is so thin that in most cases it would have broken to pieces in polishing. ”

“ These knives are usually about eighteen inches long, with a broad, sharp, murderous blade. The handles are of tortoise or ivory, often carved richly, or inlaid with figures of the Virgin, the Saviour, or the crucifix. The knife is kept open by a curious little wheel, between blade and handle, and is used indiscriminately, to slice a melon or lay bare a quarrelsome neighbor’s heart. ”