carrier stands at ɛ, the centre of the roller of the looper ૬, eccentric, through which the dotted line a ßr.

وع

passes, is also at ɛ, and this point, ɛ, will be in, from the smaller arc. The smaller arc, ag, must therefore be lengthened by, the latter having a radial direction. The shape of the eccentric is therefore dependent on the line thus described, its outer edge running parallel to this line at a distance equal to the radius of the roller. The eccentric has, at the point at which the quick return motion of the looper occurs, a sharp edge causing a jerk, to obviate which an eccentric groove is frequently made use of, thus dispensing with the spring pressing against the horizontal lever. The looper eccentric is moveable, being fastened only by a set screw to the axis. A slight shifting of the eccentric in the direction of the motion of the shaft causes the looper to recede earlier, but also to reach the needle sooner, thus increasing the distance between the upper surface of the looper from the eye of the needle when making its return motion, also diminishing the rise for the formation of the loop and increasing the distance between the point of the looper and the eye of the needle at the moment of the loop being caught. A contrary motion produces, of course, contrary results.

The eccentric cylindrical surface of the feed eccentric also consists of two concurrent concentric arcs. At the point where the eccentric is screwed on to the shaft the latter is in. in diameter, the radius of the smallest arc is therefore taken at 4 in., thus giving in. thickness to the eccentric, which is found sufficient, the eccentric being constructed of steel. Assuming the greatest length of a stitch to be in., the motion of the eccentric must be in. as it presses against the feeder centrally

5

The

between its fulcrum and the roughened foot. radius of the larger arc is therefore made to in. When the roller of the needle carrier has reached m the feed eccentric must commence its action on the feeder. The feeder being placed on the left side of its eccentric, m is the point at which the smaller curve must commence to merge into the larger one.

This transition is effected by a line running at a tangent to the smaller arc, and slightly curved at the point of concurrence with the larger one. This transition line must be so constructed as to shorten the feed motion as much as possible, that is, the centre angle m1 o m2 = 4, between which this line lies, must be as small as possible. The transition line effecting the return motion of the feeder is constructed of the same shape as the foregoing, the return requiring also to be effected as rapidly as possible. During the return the feeder must remain in its highest position, and it therefore follows that the lower boundary of the forked lever, cd, which lies between a centre angle, must be a curve. This curve" resolves itself on both sides into horizontal lines. The distance of the roller, b, from the centre of the eccentric disc is dependent on the extreme position of the forked lever. The exact position of the roller on the eccentric is ascertained from the condition that the feeder commences to rise when the looper has caught the loop securely. This corresponds to the moment at which the roller of the needle carrier has reached the point ʼn in the slot. The position of the roller being fixed, the point at which the stroke of the feeder is completed and at which the horizontal return motion must commence is easily determined. From this follows the position of

η

the point n on the feed eccentric, at which the second transition line from the larger to the smaller curve must

commence.

THE SINGLE-THREAD CHAIN-STITCH MACHINE WITH

ROTATING HOOK.

The drawing in Figs. 1, 2, and 3, Plate II. describes a single-thread chain-stitch machine with rotating hook and feed motion from below. The upper and lower parts of the machine are cast in one piece, and the main shaft, b, lies beneath the sewing plate, parallel to the axis of the machine. A connecting rod, h, attached to the hinder end of the shaft transmits motion by means of an eccentric to a bent lever, i, the front edge of which is attached to the needle carrier, k. The shape of the hook has been already described; it is attached to a stud about to in. in diameter, and in. in length, fitting into the front end of the shaft, and fixed by a set screw. The eccentric, which is cast in one piece, with a small driving-wheel and fly-wheel (Fig. 5), is attached to the hinder part of the shaft. A guide ring, g, is screwed on to the shaft close to the bearing, preventing it from shifting in the direction of its axis.

12

A slot, c, is made in the front end of the needlecarrier lever, into which a horizontal pin, ¿, Fig. 12, fits. This pin is in the form of a screw, the head of which prevents a side motion of the lever, and which, prolonged and working in a slot in the bracket head, prevents the round needle carrier from turning. The presser is constructed in a similar manner to the carrier. Its foot is screwed on, and a spiral spring pressing against the bracket head effects the pressure.

The sewing plate (Fig. 6) consists of a thin steel plate, affixed to the lower part of the machine by means of two screws, b. The main shaft projects in. beyond the lower part of the machine, and this end is turned off in an eccentric form, and fits into a square hole in the feeder, c, Fig. 2. is the looper, and on its right the stitch regulator.

2

Close in front of the feeder

The hook has a diameter of 8". Assuming the sewing plate to be "" thick, and the point of the hook in its highest position to be still in. from the lower surface of the plate, it follows that the distance of the axis of the main shaft from the surface of the sewing plate=5". The loop-forming rise of the needle being taken atin., and the distance of the eye of the needle from the looper point at the moment of the latter catching the loop at also in., it follows that the eye of the needle when in its lowest position must stand 34 below the surface of the sewing plate. Taking 2 ́ ́ as: the extreme thickness of the material to be sewn, and 2"" for the length of the point of the needle, the eye of the needle must be raised at least 4'"' above the sewing. plate, to enable the needle to clear the material. Allowing, therefore, 4"", it follows that the rise of the 41 needle carrier must be 44"+3"8". The length of the needle from the carrier to the eye is equivalent to the distance of the eye from the sewing plate, the thickness: of the material and that of the presser foot, which is 1 ́ ́ ́, making in all 64'"', but 7""' are generally allowed. The proportions of the arms of the needle-carrier lever are as 3 to 1, the rise of the eccentric must, therefore, be 23", or the distance of the centre of the eccentric from the axis of the main shaft 14". The radius of the eccentric

is composed of this distance, of the length of the radius of the circumference of the main shaft in., and of the thickness of the smallest side of the eccentric 1"", altogether 4". The diameter of the eccentric is therefore 9''. The greatest length of stitch is to be in.; the dis1B tance of the centre of the feed eccentric from the axis of the main shaft must, therefore, be in. The stud of the looper being in. in diameter, the axis of the feed eccentric falls on it, and the radius of the feed eccentric may, therefore, be taken at 13". The opening in the feeder in which the feed eccentric works is 5 square. In Fig. 13 the feeder is drawn separately.

MACHINES FOR DOUBLE-THREAD CHAIN-STITCH

May be divided, as before mentioned, into two classes. Machines of the first class are very similar to the singlethread chain-stitch machine with vibrating looper, and were first introduced in France, while those of the second class originated in America.

We have already examined the formation of the chainstitch by means of two threads, and remarked that the motion of the looper corresponds exactly to that of the looper of the single-thread chain-stitch machine. The motion of the needle is also subject to the same conditions. On this account the whole of the mechanism of a single-thread chain-stitch machine can be employed in the construction of the double-thread chain-stitch machine; the shape of the looper alone varies, which involves an alteration in the length of the motion from left to right, and therefore also in the shape of the looper eccentric. The length of the movement of the looper is in this case also composed of three parts, viz.