Technical Field

The invention relates to a portable angle grinder having an improved protective guard. Background Art

A portable angle grinder with a protective guard or cover is generally known. The protective guard protects the operator who is operating the grinder from being injured by work piece fragments. The protective guard is adjustably attached to a housing of the portable angle grinder by a clamping collar which is clamped to a bearing flange member formed on or mounted to the housing. The clamping collar has two fastening tabs which are fastened together by a clamping screw. After loosening the clamping screw, the angular position of the protective guard with respect to the housing can be adjusted.

In the known portable angle grinder described above, the clamping screw is easy to be unscrewed from the protective guard when the grinder is operated or adjusted. The unscrewed screw may be lost, and the grinder operating with a loose protective guard may create high risk to the operator.

For addressing this problem, WO 2009121432 Al discloses a hand machine tool having means for preventing the clamping screw from moving out of the clamping collar. Although the structures disclosed in WO 2009121432 Al can effectively retaining the clamping screw to the clamping collar, they are complicated. For example, most of them relate to modification of the clamping collar itself.

Thus, it is desirable to provide a simple retaining mechanism for the clamping screw of the portable angle grinder.

Summary of the Invention

In view of the problem existed in the prior art, an object of the invention is to provide a portable angle grinder having a simple but effective protective guard.

For achieving this object, in one aspect, the present invention provides a portable angle grinder comprising:

a housing,

a bearing flange member attached to the housing, and

a protective guard mounted to the bearing flange member,

wherein the protective guard comprises a guard body, an open-type clamping collar fixed to the guard body and having two fastening tabs opposed to each other, a set of clamping screw and nut for fastening the two fastening tabs near each other while leaving a gap between them, and screw retaining means for preventing the clamping screw from moving out of the clamping collar, and

wherein the screw retaining means is attached to or formed by the clamping screw.

In accordance with a preferred embodiment of the invention, by tightening or loosening the clamping screw with respect the nut, the protective guard comes into a tightened state for the operating the portable angle grinder and an adjusting state for adjusting the angular position of the protective guard with respect to the housing.

In accordance with another preferred embodiment of the invention, the nut is permanently fixed to one of the two fastening tabs of the clamping collar.

In accordance with another preferred embodiment of the invention, the screw retaining means is constituted by at least one slot formed in the outer surface of the screw rod of the clamping screw, and a retaining washer which, in an assembled state of the clamping screw and nut, is engaged in the slot within the gap between the two fastening tabs of the clamping collar.

In accordance with another preferred embodiment of the invention, the screw retaining means is constituted by a hole formed diametrically through the screw rod of the clamping screw, and a split pin which, in an assembled state of the clamping screw and nut, is inserted through the hole within the gap between the two fastening tabs of the clamping collar. In this case, after the split pin has been is inserted through the hole, at least one of the exposed ends of the split pin may be bent back so as to lock the split pin to the clamping screw.

In accordance with another preferred embodiment of the invention, the screw retaining means is constituted by a washer which is fixed to the screw rod of the clamping screw at a position within the gap between the two fastening tabs of the clamping collar. In this case, the washer may be permanently fixed to the screw rod by point welding.

In accordance with another preferred embodiment of the invention, the screw retaining means is constituted by a threaded hole formed through one of the two fastening tabs which is near the screw head of the clamping screw. The screw rod of the clamping screw has a non-threaded segment near the screw head of the clamping screw and a threaded segment near the tip end of the clamping screw, the non-threaded segment being slidable in the threaded hole, and the threaded segment being threadingly engageable with the threaded hole. In this case, the lengthwise dimensions of the non-threaded segment and threaded segment of the screw rod of the clamping screw may be determined so that the threaded hole and the nut do not threadingly engage with the threaded segment simultaneously.

In accordance with another preferred embodiment of the invention, the screw retaining means is constituted by an enlarged tip end of the screw rod of the clamping screw formed after the clamping screw has been screwed through the nut and the tip end has been exposed from the nut. In this case, the screw rod of the clamping screw may be long enough so that there is a gap between the enlarged tip end and the nut in the tightened state of the protective guard. Also in this case, the enlarged tip end may be formed by crimping or point welding.

In another aspect, the present invention provides a portable angle grinder comprising: a housing,

a bearing flange member attached to the housing, and

a protective guard mounted to the bearing flange member,

wherein the protective guard comprises a guard body, an open-type clamping collar fixed to the guard body and having two fastening tabs opposed to each other, a set of clamping screw and nut for fastening the two fastening tabs near each other while leaving a gap between them, and screw retaining means for preventing the clamping screw from moving out of the clamping collar, and

wherein the screw retaining means is constituted by a bent plate which is weld onto the clamping collar behind the screw head of the clamping screw after the clamping screw has been engaged with the nut.

In accordance with a preferred embodiment of the invention, the bent plate has a portion which protrudes radially from the clamping collar to a position facing a part of the screw head of the clamping screw but not obstructing the manipulation to the screw head.

In accordance with the above aspects of the invention, the protective guard of the portable angle grinder has screw retaining means which is attached to or formed by the clamping screw or formed on the clamping collar near the clamping screw. As a result, a simple and compact screw retaining structure can be obtained. The clamping screw is effectively prevented from moving out of the clamping collar, and it is easy to assemble and adjust the protective guard of the portable angle grinder.

Brief Description of the Drawings

The invention will be further understood by reading the following detailed description with reference to the drawings in which:

Fig. 1 is a schematic plane view showing a part of a portable angle grinder according to a preferred embodiment of the invention;

Fig. 2 is a schematic plane view showing a protective guard of the portable angle grinder of Fig. 1;

Fig. 3 is a schematic perspective view showing a bearing flange member of the portable angle grinder of Fig. 1;

Fig. 4 is a schematic view showing screw retaining means according to a preferred embodiment of the invention;

Fig. 5 is a schematic view showing the screw retaining means of Fig. 4 in use;

Fig. 6 is a schematic view showing screw retaining means according to another preferred embodiment of the invention;

Fig. 7 is a schematic view showing screw retaining means of Fig. 6 in use;

Fig. 8 is a schematic view showing screw retaining means according to yet another preferred embodiment of the invention;

Figs. 9 and 10 are schematic views showing screw retaining means according to yet another preferred embodiment of the invention;

Fig. 11 is a schematic view showing screw retaining means according to yet another preferred embodiment of the invention;

Fig. 12 is a schematic view showing the screw retaining means of Fig. 11 in use; and

Fig. 13 is a schematic view showing screw retaining means according to yet another preferred embodiment of the invention.

Detailed Description of Preferred Embodiments

Now, a portable angle grinder according to a preferred embodiment of the invention will be described with reference to Figures 1 to 3.

As shown in Fig. 1, a portable angle grinder comprises a housing 100, a rotary shaft 200 mounted to the housing, a grinding wheel (not shown) to be mounted to the rotary shaft, a bearing flange member 300 fixedly mounted to or formed integrally with the housing, and a protective guard 400 adjustably mounted to the bearing flange member.

As shown in Fig. 2, the protective guard 400 comprises a guard body or cover 7, an open-type clamping collar 2 fixed to the guard body 7 and having two fastening tabs 4 and 5 opposed to each other, and a clamping screw 3 and a clamping nut 6 for fastening the two fastening tabs 4 and 5 near each other while leaving a gap between them.

The two fastening tabs 4 and 5 are protruded radially from the main body of the clamping collar 2 and are each formed with a through hole to be inserted through by the clamping screw 3.

The clamping nut 6 is preferably permanently fixed to one of the two fastening tabs 4 and 5 of the clamping collar 2 (in the illustrated embodiments, permanently fixed to the right-hand fastening tab 5).

The guard body 7 has a half-disc shape with a central hole defining an inner circumference. Protrusions 71 are formed in the inner circumference of the guard body 7. The clamping collar 2 is fixed to, for example, welded to, the back side of the guard body 7 along the inner circumference of the guard body 7. The clamping collar 2 has at least one inner tooth 8 (three shown in Fig. 2).

As shown in Fig. 3, the bearing flange member 300 has a portion 310 protruded in the direction of the rotary shaft 200. In the embodiment shown in Fig. 3, the protruded portion 310 is formed in two layers, an upper layer and a lower layer, having the same outer diameter or different outer diameters. The protruded portion 310 is formed with recesses in its outer circumferential surface in a direction parallel with the central axis of the rotary shaft 200. The recesses in the outer periphery of the upper layer comprise wide recesses 9a and narrow recesses 9b, while the recesses is the outer periphery of the lower layer comprise only narrow recesses. Further, a circular recess 9c is formed between the upper and lower layers. However, the structure of the protruded portion 310 is not limited to this, only one layer or more than two layers are also applicable.

When the clamping collar 2 is mounted to the bearing flange member 300 at a fixed position, with the one or more inner teeth 8 passing through corresponding wide recess 9a formed in the outer periphery of the upper layer and coming into the circular recess 9c formed between the upper and lower layers, the inner circumference of the guard body 7 is arranged around the two layers of the protruded portion 310.

Then the clamping screw 3 is inserted through the through holes of the two fastening tabs 4 and 5 and is screwed into the clamping nut 6. By tightening the clamping screw 3, the inner tooth 8 of the clamping collar 2 engages into the recess 9c formed between the upper and lower layers of the protruded portion 310 of the bearing flange member 300, and the protrusions 71 formed in the inner circumference of the guard body 7 are engaged into recesses formed in the outer peripheries of both layers of the protruded portion 310. In this way, the angular position of the protective guard 400 with respect to the housing 100 is set. By engaging the protrusions 71 of the clamping collar 2 into different recesses formed in the outer peripheries of both layers of the protruded portion, the angular position of the protective guard 400 is adjusted.

Conventionally, the clamping screw 3 is a standard screw with fully threaded rod. The clamping screw is easy to screw out of the protective guard when operating the grinder or adjusting the angular position of the protective guard.

According to the invention, screw retaining means is provided for preventing the clamping screw 3 from moving out of the clamping collar 2.

As shown in Figs. 4 and 5, according to a preferred embodiment of the invention, the screw retaining means is constituted by slots 12 formed in the outer surface of the screw rod of the clamping screw 3 and a screw retaining washer 10 to be engaged into the slots 12. The clamping screw 3 may be either fully threaded or partly threaded. The retaining washer 10 may be a standard (for example, DIN 6799) open-type elastically deformable retaining washer.

In the assembled state shown in Fig. 5, the clamping screw 3 is fastened to the clamping nut 6, and the screw retaining washer 10 is engaged with the slots 12 of the clamping screw 3 by elastic deformation. The retaining washer 10 can always keep the clamping screw attached to the clamping collar 2.

The position where the retaining washer 10 touches the left-hand fastening tab 4 of the clamping collar 2 defines a delivery state for the transferring the grinder which is also an adjusting state for putting the protective guard around the bearing flange member and rotating it for positional adjustment. When permitted by dimensions, there is always a pre-load between the clamping screw 3 and the clamping nut 6, even when the clamping screw 3 is not completely screwed into the clamping nut 6 in the delivery state of the protective guard.

This embodiment has another advantage, that is, the clamping screw 3 is easy to be exchanged.

As shown in Figs. 6 and 7, according to another preferred embodiment of the invention, the screw retaining means is constituted by a hole 21 formed diametrically through the screw rod of the clamping screw 3 and a split pin 22. After the clamping screw 3 is fastened to the nut 6, the split pin 22 is inserted through the hole 21 which is located between the two fastening tabs 4 and 5 of the clamping collar 2. Then, the exposed ends of the two legs of the split pin 22 are bent back, as shown in Fig. 7, so as to lock the split pin 22 to the clamping screw 3. The split pin 22 can always keep the clamping screw attached to the clamping collar 2.

In this embodiment, the clamping screw 3 may be either fully threaded or partly threaded.

The split pin 22 may be a standard (for example, ISO 1234/DIN 94) split pin. This embodiment also has advantage of easy exchanging of the clamping screw.

As shown in Fig. 8, according to yet another preferred embodiment of the invention, the screw retaining means is constituted by a washer 31 which is fixed to the screw rod of the clamping screw 3 at a position between the two fastening tabs 4 and 5 of the clamping collar 2.

The washer 31 can be fixed to the screw rod of the clamping screw 3 in any manner known in the art, for example, by point welding, as indicated by reference numeral 32 in Fig. 8. Preferably, 3 or 4 point- welding is adopted here.

The welded washer 31 can prevent the clamping screw from moving out of the clamping collar 2.

The disadvantages of this embodiment are that it is not convenient to perform welding in such a narrow space and it is difficult to exchange the clamping screw.

As shown in Figs. 9 and 10, according to yet another preferred embodiment of the invention, the screw retaining means is constituted by a bent plate 41 which is fixed to, for example, weld to, the clamping collar 2 behind the screw head of the clamping screw 3 after the clamping screw 3 has been fastened to the nut 6.

The bent plate 41 has a portion 42 which protrudes radially from the clamping collar 2 to a position facing a part of the screw head of the clamping screw 3 but not obstructing the manipulation to the screw head. The portion 42 can prevent the clamping screw from moving backwardly out of the clamping collar 2.

This embodiment has a disadvantage, that is, it is difficult to exchange the clamping screw.

As shown in Figs. 11 and 12, according to yet another preferred embodiment of the invention, the screw retaining means is constituted by forming the through hole in one of the two fastening tabs 4 and 5 which is near the screw head of the clamping screw 3 (in the embodiment shown in Figs. 11 and 12, the left-hand fastening tab 4) as a threaded hole 53. The threaded hole 53 has an inner diameter equal to that of the clamping nut 6. The clamping screw 3 is partly threaded. That is to say, the screw rod of the clamping screw 3 has a non-threaded segment 52 near the screw head of the clamping screw and a threaded segment 51 near the tip end of the clamping screw. The non-threaded segment 52 has an outer diameter which is smaller than the minor diameter of thread on the threaded segment 51 (the minor diameter being measured at the bottom of the thread). When assembling, the threaded segment 51 is completely screwed through the threaded hole 53. Then the non-threaded segment 52 is slidable in the threaded hole 53 but the whole clamping screw 3 cannot move out of the clamping collar 2 by itself. This state can be referred to as delivery/adjusting state of the protective guard. Then, the threaded segment 51 is fastened into the nut 6 so that the protective guard comes into its tightened state.

In this embodiment, the lengthwise dimensions of the segments of the screw rod of the clamping screw are determined so that the threaded hole 53 and the nut 6 do not threadingly engage with the threaded segment 51 simultaneously. Otherwise, the protective guard cannot be tightened.

In this embodiment, the clamping screw 3 can be exchanged easily.

As shown in Fig. 13, according to yet another preferred embodiment of the invention, the screw retaining means is constituted by enlarging the tip end 61 of the screw rod of the clamping screw 3 after the clamping screw 3 has been screwed through the nut 6 and the tip end 61 has been exposed from the nut 6. The enlarging of the tip end 61 may be performed in any manner known in the art, for example by crimping the tip end or by point welding on the tip end.

The enlarged tip end 61 will prevent the whole clamping screw from moving out of the nut 6. The length of the screw rod of the clamping screw should be long enough so that there is a gap between the enlarged tip end 61 and the nut 6 in the tightened state of the protective guard. This gap is essential for adjusting the angular position of the protective guard.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.