The peculiar form of the insides of the blades is in all cases of paramount importance, and in the manufacture of fine scissors is attended to by a person called a 'putter-together,' whose pro-vince it is to examine the screw-joint, and see to the form of the riding-places, and lastly to set the edges of the scissors, which for general purposes arc sharpened on an oilstone at an angle of about 40 degrees, but for the fine scissors more nearly upright or at 30 degrees from the perpendicular.
So important indeed is the configuration of the inner face of scissors, that they should never be ground or meddled with at that part, but by a person fully experienced in their action, and scissors may with careful usage be kept in order for years, without being ground, if the edges are occasionally set on the oilstone at the inclination above referred to. It will frequently happen that well-made scissors which appear to grate a little when closed, merely do so from dirt or dust, which if removed by passing the finger along the edges, will restore the scissors to their smooth and pleasant action.
It seems quite uncalled for to enter into the separate description of various instruments known as button-hole scissors, cutting-out, drapers', flower, garden, and grape scissors, horse trimming scissors; hair, lace, lamp, nail, paper, pocket, stationers', and tailors' scissors, and many others; nor of the large shears for the garden such as pruning, trimming, and border shears, the distinctions between which varieties are sufficiently known to those who use the several kinds, but the author will merely notice such of them as present any peculiarity of structure.
Button-hole scissors are notched out towards the joint screw as in fig. 914, so as to enable the instrument to make an incision a little distant from the edge of the material; the joint must be made stiff, so as to prevent the points catching against each other.
Flower and grape scissors assume the section of fig. 913, so that they first cut the stem, and then hold it like a pair of pliers, the one blade requires to be made in two parts riveted together; when entirely closed they present an elliptical section a; and b shows how the stem of the flower is grasped, the blades are rounded at all parts that they may not injure the plants.
Lamp scissors have the one blade very broad, and with a little rim to prevent the snuff of the lamp falling on the carpet.
Nail scissors for the dressing-case, are made very strong and with short blades. In using scissors formed in the ordinary mode, the fingers and thumb of the right hand, have naturally a tendency to press the blades together, in that position in which they arc intended to cut; but the left hand on the contary has a tendency to separate the blades and defeat the principle on which scissors act. Therefore nail scissors are made in pairs, and formed in opposite ways, or as "rights and lefts," so that they may suit the respective hands.
Pocket scissors have blades which admit of being locked together in the form represented in fig. 915, as the point of the one blade catches into a small spring near the bow of the other; and the instrument cannot be opened until the spring or catch is released with the nail. When closed for the pocket, the bows stand on one line as at a b, when opened for use as at a c.
Surgical scissors are of many forms, but have generally short blades and long straight slender handles, that the hand may not impede the vision. In some of the surgical scissors the blades are curved as scimitars, and others arc curved sideways, these kinds are difficult to make, as the elasticity of contact in the blade is required nevertheless to be maintained.
Many of the shears and scissors used in gardening, only differ from scissors and shears in general in their size, and the adaptation of their handles, some of which are of wood, and placed at an angle of 40 or 50 degrees, as in the letter Y inverted. Other garden shears used in trimming borders, have handles a yard long and inclined about 80 degrees to the blades, which may therefore lie on the ground whilst the individual stands nearly erect. Some of the border shears have rollers to facilitate their movement along the ground.
In pruning shears and scissors, two peculiarities of form are judiciously introduced. In the more simple of the two kinds, which is shown in fig. 916, the one part of the instrument terminates in a hook, with a broad and sometimes a roughened edge, to retain the branch from slipping away, the other part of the instrument is formed as a thin cutting blade, the edge of which is con-vex. Theoretically it should be part of a logarithmic spiral, in which case the edge of the cutter would present a constant angle to the work throughout its action, and slide laterally through the incision made by itself, or make a sliding cut, whereas if the edge of the blade were radial, it would make a direct cut without any sliding, as in a paring chisel. The spiral blade cuts more easily, and -will therefore remove a larger branch, with an action precisely analogous to that of the oblique cutters in some of the planes, although differently produced.
Some of these instruments when a little modified in form, are mounted on poles from 6 to 10 feet long, and are actuated by a catgut; this tool which is known as the Averuncator, is very efficient for pruning at a considerable distance above the head.
The other pruning shears represented in fig. 917, are denominated sliding shears, the pin that unites the two parts, fits in a round hole in the one blade and a long mortise in the other, and a link or bridle-rod c e, is attached by a screw to each lever; in consequence, when the instrument is fully opened the pin or fulcrum is at the end a, of the mortise, whereas, on the shears being gradually closed, the cutting blade slides downwards upon the pin until the fulcrum is near the opposite end b. In this modification of shears the sliding action is produced to a much greater extent than with the spiral blade, but the construction is a little more expensive; and as the instrument is not provided with bows for the fingers, the spring d e, is added to throw it open.
Before dismissing this section, two modifications of shears will be briefly adverted to; those used by card makers, and the revolving shears employed in manufacturing woollen cloth.
Card paper is prepared in large sheets; when dried and pressed it is cut into square pieces of the required sizes by means of long shears, the one blade of which is fixed at the end of a table, and has the joint at the farther extremity, whilst the cutting blade has a handle in front, and moves through a loop to keep the blade in its position, as in some chaff-cutting machines; there is also a stop fixed parallel with the blades, and as distant as the width of the slips into which the card is first divided, and these slips are then cut again the lengthway of the cards. The shears are moved so rapidly, that the action sounds like that of knocking at a door, and still the cards agree most rigidly in size.
Revolving shears or "perpetual shears** are used for shearing off the loose fibres from the face of woollen cloths. For narrow cloths the cylinders are 30 inches long and 2 in diameter, eight thin knives are twisted around the cylinders, making 2 1/4 turns of a coarse screw, and are secured by screws and nuts which pass through flanges at the ends of the axis: formerly the cylinders were grooved and fitted with several thin narrow plates of steel 6 or 8 inches long. The edges of the eight blades are ground so as to constitute parts of a cylinder, by a grinder or strickle fed with emery, passed to and fro on a slide parallel with the axis of the cylinder, which is driven at about 1200 turns in the minute.
In use, the cylinder revolves about as quickly, and in contact with the edge of a long thin plate of steel, called the ledger blade, which has a very keen rectilinear edge, measuring 40 to 50 degrees, the blade is fixed as a tangent to the cylinder, and the two are mounted on a swing carriage with two handles, so as to be brought down by the hands to a fixed stop. The edge of the ledger blade is sharpened, by grinding it against the cylinder itself with flour emery and oil, by which the two are sure to agree throughout their length.
The cloth, before it goes through the process of cutting, is brushed so as to raise the fibres, it thru passes from a roller over a round bar, and comes in contact with the spring bed, which is a long elastic plate of steel, fixed to the framing of the machine, and nearly as a tangent to the cylinder, this brings the fibres of the cloth within the range of the cutting edges, which reduce them very exactly to one level. The machine has several adjustments, for determining with great nicety, the relative positions of the cylinder, ledger-blade and spring-bar, but which could not be conveyed without elaborate drawings. Formerly the cloth was passed over a fixed bed having a nearly sharp angular ridge, but which mode was far more liable to cut holes in the cloth than the spring-bed.
Broad cloths require cylinders 65 inches long, and machinery of proportionally greater strength. In Lewis's patent cross-cutting machine, the cloth is cut from list to list, or transversely, in which case the cloth is stretched by hooks at the two edges, and there are two spring beds; the cylinder in this machine is 40 inches long, and the cloth is shifted that quantity between every trip until the whole piece is sheared. The perpetual shears are also successfully applied to coarse fabrics including carpets.*
A modification of the above revolving shears, made in a much less exact manner for mowing grass lawns, is fitted up somewhat as a wheel-barrow, or hand truck, so that the rotation of the wheels upon which the machine is rolled along, gives motion to the shears, which crop the grass to a level surface.