GB2162550A - Lower hook for making a whipstitch in sewing machines - Google Patents

Abstract

A lower hook 1 for use in a whipstitch sewing machine having also an upper hook 2 wherein the lower hook has a substantially wedge-shaped outer end 8 and is provided with chamfered surfaces 11, 12, 13 to facilitate passage of the upper hook and a needle. <IMAGE>

Description

SPECIFICATION Lower hook for making a whipstitch in sewing machines Background of the Invention The present invention relates to a lower hook for making a whipstitch in sewing machines, in particular sewing machines of the industrial type.

As is known, sewing machines of the industrial type have three main elements for forming the stitches: the needle, the upper hook and the lower hook. These elements can all or partly be provided with threads which are combined so as to form various types of stitches. In particular, the present invention is concerned with the said elements provided for forming whipstitches with two or three threads (No. 503 or No. 504 in the Federal Standard Catalog). More specifically, the subject of the present invention is the structure of the lower hook for forming the said stitches. The latter is always provided with its own thread and has an oscillatory movement which always occurs below the plane in which the fabric lies. Both the upper hook and the needle pass close to the lower hook, during its movements.

The shape of the lower hook is a determining factor as regards operation of the entire sewing machine. In fact, on the one hand, the lower hook must oscillate according to a trajectory which almost intersects those of the upper hook and needle so as to allow the thread to be taken up and the stiches to be formed, and, on the other hand, it must avoid forced contact with the said upper hook and needle. This forced contact can lead not only to vibration, overheating and similar phenomena, but also actual jamming of the sewing machine. This jamming may occur as a result of incorrect handling by the operator who may tension the fabric being sewn and thus create slight stresses in the said elements which form the whipstitch.

The known sewing machines are not completeiy satisfactory from this point of view, since the loss of stitches or, on the other hand, vibration between the elements which form the stitches frequently occurs.

Almost always the said lower hook is a determining factor in these mishaps.

In view of the above, the general aim of the present invention is to design a lower hook for forming a whipstitch with two or three threads, which is able to overcome sustantially the abovementioned drawbacks, i.e., which is able to ensure that the sewing machines in which it is used operate with precision and in a reliable manner.

Within the scope of this general aim, an important object of the present invention is to design a lower hook for making a whipstitch, which has a simple structure and can be easily produced, using simple operations, by the industries in the sector.

These and other objects, which will become clear below, are achieved by means of a lower hook for making a whipstitch in sewing machines, comprising an end provided with a pointed projection which is substantially wedge-shaped and projects on that side of the said lower hook which the upper hook passes close to, and wherein provision is made, in the vicinity of the said tip, for a plurality of chamfers designed to facilitate both the passage of the said upper hook and the passage of the said needle.

Description ofthe Drawings Further characteristic features and advantages will become clearer from the description of a preferred embodiment of the invention, iliustrated by way of example in the attached drawings in which: Figure 1 shows a perspective view of all the elements and associated actuating parts which form a whipstitch with two threads (continuous lines) and three threads (broken lines), Figure 2 shows Figure 1, in part, and the trajectories of the said elements, Figure 3 shows a sewing machine needle and its trajectory in relation to the end of the upper hook and of the lower hook, Figure 4 shows a perspective view of the lower hook which is the subject of the present invention, Figure 5 shows the end part of the lower hook of Figure 4, in the vicinity of the end part of the corresponding upper hook, Figure 6 shows a side view of the end of the lower hook of Figure 5, with the hook in an inverted position compared to Figure 4, Figure 7 shows a plan view of the hook shown in Figure 6, and Figures 8, 9 and 10 illustrate, in perspective, certain stages during formation of a whipstitch.

Description of the Invention With reference to the abovementioned figures, the main elements which combine to form a whipstitch in a sewing machine of the industrial type are shown in Figure 1. These consist of a lower hook 1, which is the subject of the present invention, an upper hook 2 which can either be of the blind type, without thread, or provided with thread, and a needle 3. The elements 1,2 and 3 are shown connected to the parts which are most directly involved in controlling the movements of the said elements.

The trajectories of the lower hook 1, upper hook 2 and needle 3 are shown in Figures 2 and 3 and are also known per se.

In an original manner, according to the present invention, the lower hook 1 has a shape defined by a curved upright 4 and by a blade 5 which is substantially linear and which has an end 6 provided with a hole 7 through which the thread passes (Figure 4).

The end 6 is shaped as shown in Figure 5: it has a pointed projection 8 protruding on that side of the lower hook 1 which the upper hook 2 passes close to. The pointed projection 8 defines a guide face 9 which is shaped so as to be inclined relative to the main direction in which the blade 5 extends. The hole 7 is located in this guide face 9. Overall, the pointed projection 8 has the shape of a wedge on which the thread 10 ofthe said lower hook 1 partially rests, as shown in Figures 8 to 10. The guide face 9 is advantageously inclined relative to a vertical plane so as to taper slightly the pointed projection 8 in the direction of the lower edge of the blade 5. As is shown in Figure 5, the hole 7, in a plan view from the top, is not visible in fact, whereas, on the other hand, it can be seen in a plan view from the bottom, and is clearly shown in Figure 7.

Provision is also made for a plurality of chamfers arranged in the vicinity of the end 6 of the blade 5, substantially behind the pointed projection 8.

These chamfers consist of a first and second chamfer 11 and 12 providedforfacilitating passage of the upper hook 2, and of a third chamfer 13 for passage of the needle 3.

In detaii, the first chamfer 11, which is particularly visible in Figure 7, consists of a tapered portion of the blade 5, adjacent to and located beneath the overlying pointed projection 8. In practice, the thickness of the blade 5 in this zone, is relatively smaller than in its remaining part. The chamfer 11 thus enables easy insertion and passage of the curved tip 14 of the upper hook 2, whether the latter be blind or provided with a hole, which tip matches the shape of the pointed projection 8. It can be seen that the profile of the first chamfer 11 is an increasing linear profile extending from the said tapered portion of the blade 5 adjacent to and located beneath the overlying pointed projection 8.

The lower hook 1 is engaged by the passage of the upper hook 2 initially in the region of the first chamfer 11 and then in the region of the second chamfer 12, which is arranged on the upper edge of the blade 5, on that side of the blade itself which is next to the pointed projection 8.

In detail, the chamfer 12 is inclined so as to cause tapering of the upper edge of the blade 5. The third chamfer 13 is arranged substantially in the same zone as the second chamfer 12, but on the side of the blade 5 on which the pointed projection 8 is not provided, as can be seen from Figure 5. This third chamfer 13 is associated with the passage of the needle 3, as can be seen from Figure 3. It is in fact known that the lower hook 1 inserts itself in a slot or recess 3a of the needle 3 (Figure 8) and that the needle itself moves upwards while the lower hook 1 is still adjacent to it. It is precisely to prevent interference between the lower hook 1 and the lower end of the slot 3a that the third chamfer 13 is provided. The operation of the elements, which is the subject of the present invention, is clear from what has already been described above.As Figure 8 shows, the lower hook 1 initially passes close to the needle 3 in the region of its slot 3a and inserts itself between the said needle 3 and its associated thread.

Immediately after thins has happened, the needle 3 moves upwards again, following the inclined trajectory shown in Figure 3. The possibility of interference between the lower end of the slot 3a of the needle 3 and the upper edge of the lower hook 1 is thus obvious. This interference, however, is prevented by the third chamfer 13.

Subsequently, the upper hook 2 passes close to the lower hook 1, on the side where the pointed projection 8 is located (Figures 5 and 9). The upper hook 2 can be of the type to which thread is attached, as in the case of Figures 5 and 9, or can be blind and provided with an end fork. In any event, it is possible, as a result of any pulling or tensioning of the fabric being sewn, for the upper hook 2 to interfere with the lower hook 1 and become caught up with it. This extremely negative occurrence is prevented by the first chamfer 11, which is followed by the second chamfer 12. Moreover, the latter allows the two hooks to be gradually separated should they accidentally come into contact with each other.The chamfers shown, in particular the first chamfer 11 and the second chamfer 12, are of fundamental importance when hooks which have the shape shown in Figure 5, i.e. are rounded at the end, are used. In fact, any oscillations and/or deviations of these hooks, in the absence of the said chamfers, would inevitably result in not only light contact and/or rubbing between the parts in relative motion, as occurs for substantially flattened hooks of the known type, but also actual interference between the said elements with vibration in the area where the portions which project the most are located. The invention thus achieves the proposed objects. Attention is drawn to the fact that the significant operational improvements achieved are obtained by providing appropriate chamfers which are suitably located and are such that they do not weaken substantially the strength of the lower hook 1.

All of the details can be relaced by technically equivalent elements. In practice, the materials used can be of any type and the dimensions of any magnitude, as required.

Claims (7)

1.A A lower hook for making a whipstitch in sewing machines having an upper hook, comprising an end provided with a pointed projection which is substantially wedge-shaped and projects on that side of the said lower hook which the upper hook passes close to, and wherein there is provided, in the vicinity of the said tip, a plurality of chamfers designed to facilitate both the passage of the said upper hook and the passage of the said needle.

2. A lowet hook as claimed in claim 1, wherein there is a first chamfer which is adjacent to and located beneath the said overlying pointed projection, the said first chamfer being such that it reduces the thickness of the portion concerned of the blade of the said lower hook.

3. A lower hook as claimed in claim 2, wherein the said first chamfer extends, with an increasing linear profile, from the said portion of the said blade which is adjacent to and located beneath the said overlying pointed projection.

4. A lower hook as claimed in claim 1, wherein a second chamfer is present on the upper edge of the blade of the hook itself, in a position immediately adjoining the said pointed projection, the said second chamfer being such that it tapers the said upper edge.

5. A lower hook as claimed in claim 1, wherein there is provided a third chamfer which is arranged on that side of the said hook where the said pointed projection is not located, on the upper edge of the said hook, the said third chamfer being arranged so as to taper the said upper edge.

6. A lower hook as claimed in claim 1, wherein the said pointed projection has a guide face inclined towards the lower edge of the said lower hook.

7. A lower hook for making a whipstitch in sewing machines, substantially as hereinbefore described with reference to the accompanying drawings.