GB2134038A - Motorised saw - Google Patents

Abstract

A motorised saw comprises a motor drive portion mounted in a housing which is provided with a hand-grip, and two driven cutting blades which are releasably connected to the motor drive portion. In order to achieve a large cutting capacity and to be able to handle the saw without difficulty, the cutting blades are formed as reciprocating driven saw blades (1, 2) with teeth (3) set to project out beyond the blade faces with the blades having their back edges guided in a guide rail (4) extending over the whole length of the saw blades, and with the width of the backing guide rail (4) lying within the saw tooth profile. The two reciprocating saw blades (1, 2) are driven in mutually opposite directions and are held in mutual sliding contact by the guide rail (4). <IMAGE>

Description

SPECIFICATION Motorised saw This invention relates to a motorised saw comprising a motor drive portion mounted within a housing which is fitted with a hand-grip and two driven cutting blades which are releasably connected to the motor drive portion.

Many different types of motorised saw are known, but they all have disadvantages which are specific to this type of saw.

Circular saws, if designed for use as hand-saws, are dangerous to handle and are not suitable for cutting through relatively thick objects, such as tree trunks. In order to be able to use such saws for that type of work the circular saw has to be provided with a correspondingly large saw blade and must be rigidly mounted. Such fixed saws cannot be guided by hand.

Chain saws comprise a sabre on which a chain set with saw teeth circulates in a groove at high speed. Thicker objects, such as tree trunks, can be cut with such saws. However, the chain suffers a very high degree of wear on the chain links.

Therefore, the links continually need to be retightened. One also cannot avoid the need to provide continuous lubrication with high-grade lubricating oil, since otherwise the sabre will overheat, and possibly run blue and become damaged. The handling of chain saws is difficult and dangerous, since the chain runs free at the upper and lower sides. The considerable weight of the sabre and chain must be coped with by the motor drive. It often happens that the chain breaks during use. The flying ends of the chain then represent a considerable hazard. Consequently, special strong protective clothing must be used when handling chain saws.

The known cross-cut saws are considerably easier to handle in comparison with the aforementioned types of saw. However, they can only be used for cutting wood which is a few centimetres thick.

Hedge-clippers are also known which have laterally projecting teeth on each side of a central retaining device, in the manner of a mower beam, with the teeth being provided on two cutting blades driven in opposite directions. The toothing is very large since with these hedge-clippers one is designing them predominantly to cut green branches, for which purpose a shearing cut is desirable. However, the blade of these shears can very easily recoil or kick back with thicker branches. There is then again a hazard to the operator. The handling of such hedge-clippers requires the exertion of correspondingly large holding and guiding forces, since the whole shears can be mounted only on the motor drive housing.

Even if one was to provide these known hedgeclippers with smaller teeth, they would not be suitable for the sawing of thicker pieces of wood, since their holding device is substantially thicker than the two cutting blades and consequently would prevent a deeper penetration into the wood.

It is an object of the present invention to provide a motorised saw of the type first referred to above which on the one hand has the advantageous cutting capacity of a chain saw and which on the other hand is as easy and simple to handle as a cross-cut saw.

This object is achieved in accordance with the present invention by a motorised saw comprising a motor drive portion mounted within a housing which has a hand-grip, and two reciprocatingly driven saw blades with teeth set to project out beyond the blade faces and arranged to move in opposed directions, in which the saw blades are releasably connected to the motor drive portion, in which the back edges of the saw blades are guided in a guide rail fixedly connected to the housing and extending over the whole length of the saw blades thereby to hold the saw blades in mutual sliding contact, and in which the width dimension of the guide rail lies within the saw tooth profile.

Such a motorised saw can be handled easily and comfortably. By means of the guide rail the saw blades experience a corresponding strengthening and increased guidance without the guide rail thereby preventing the deeper penetration of the saw blades into the workpiece, since the guide rail does not project laterally outside the saw tooth profile.

The reciprocating saw blades sliding along one another, in combination with the guide rail which guides and appropriately stiffens the blades, ensures a large cutting capacity combined with ease of handling of the saw.

According to a further preferred feature of the invention, the saw blades are each provided along their longitudinal back edges with a guide flange of about half the width of the respective saw blade, in the blade region between the guide flanges and teeth the blades are held together along the blade length by a plurality of slot-pin connections, the pins of which are fixedly connected to the faces of the saw blades, the guide flanges are slidingly received in a common closed groove defined by two mirrorsymmetrically formed rebated backing strips which together form the guide rail, the saw blades at their ends remote from the drive means are held in said groove by means of a releasable slot-pin coupling which extends through the two saw blade guide flanges and both backing strips, and the outer faces of the backing strips and also the heads of the pins of the slot-pin coupling are flush with the outer faces of the two saw blades.

In contrast to the two cutting blades of a hedge-clippers, the saw blades, by appropriate toothing and setting of the teeth, ensure that the saw will not recoil when sawing through thick branches and will cut freely with a sufficiently wide cutting gap. Their particular advantage, as compared with hedge-clippers, and also with respect to chain saws, lies in the fact that the saw blades have saw teeth along one longitudinal edge only, while the longitudinal edge opposite that which bears the teeth, i.e. the back edge, lies within the guide rail which is stationary and can therefore be grasped without danger. The likelihood of accidents is therefore very small.

Nevertheless, the motorised saw of the present invention performs the work of a chain saw without any difficulty. Since the slot-pin connections do not extend laterally beyond the outer faces of the two saw blades, and since also the two rebated backing strips which make up the guide rail are flush with the outer faces of the two saw blades, the part of the saw which comprises the saw blades and the guide rail is nowhere thicker than the thickness of the two saw blades themselves. Since the saw blades have teeth set out at least partially beyond their blade outer faces, this portion of the saw will guide itself through deep saw cuts without binding, and the thickness of the wood or tree trunk which can be cut through by the saw is limited only by the length of the two saw blades.The slot-pin connection between the two saw blades and the rebated backing strips, which is provided at the end of the blades remote from the drive means, gives the necessary certainty that the saw blades and the guide rail will remain united together if the saw blades should become locked, for example in the cut.

Preferably, the slot-pin connections between the two saw blades comprise pins riveted into one saw blade and slots provided in the other saw blade, with the slots being longer than the stroke of the blades and the slots being enlarged to form a hole increased to the diameter of the pin head at at least that end of each slot nearer the drive means. By this means the individual saw blades can be separated easily from each other and can be resharpened or reset as the need arises. To accomplish this the saw blades need only to be separated from the motor drive and thereafter can be displaced relative to one another sufficiently far that the or each of the pin heads is moved to project through the enlarged hole at the end of the slot or slots.

The saw blades can become locked together in use under certain circumstances, for example with very damp wood or if the motorised saw is tilted for the sawing operation. In order to keep the frictional resistance of the two saw blades as small as possible under such extreme circumstances, it is desirable if an anti-friction film or layer, for example of tetrafluoroethylene or other self-lubricating and/or friction-reducing material, is provided between the two saw blades.

A hand-grip, preferably removable, may be fitted on to the guide rail which encompasses the back edge of the saw blades, with the hand-grip being positioned at an appropriate distance from the motor drive housing. This improves the handling of the saw, particularly in the case of long saw blades, since the guidance of the saw blades and the exertion of pressure on the saw blades does not need to be taken up on the housing of the motor drive and consequently over a long mechanical lever arm.

The motorised saw can be mounted rigidly either on the motor drive housing or, possibly, on the guide rail, so that it can be set up for example in the manner of a table saw or a pendulum saw or in some other way.

An embodiment of motorised saw in accordance with the invention will now be described in detail by way of example and with reference to the drawings. In the drawings: Fig. 1 is a side view of an embodiment of saw in accordance with the invention without the motor drive being illustrated; Fig. 2 is a front end view of the saw shown in Fig. 1; Fig. 3 is a side view of one of the saw blades; Figs. 4 and 5 are side views of the two rebated backing strips which form the guide rail; Fig. 6 is a side view of a quick-action coupling for the connection of a motor drive; Fig. 7 is a sectional view taken along the line VIl-VIl in Fig. 6; and, Fig. 8 is a top plan view of a complete motorised saw with auxiliary hand-grip.

The motorised saw shown in Figs. 1 to 8 comprises two reciprocating motor-driven saw blades 1 and 2 movable in opposite senses relative to one another. The saw blades 1, 2 are provided with conventional saw teeth 3 which may be straight or inclined forwards or backwards at an angle to the longitudinal edge of the blade.

For each blade the saw teeth 3 are set outwardly to one side of the blade in such a way that at least some of the teeth project out beyond the main plane of the outer faces of the saw blades I and 2 in order thereby to ensure a free cutting action when sawing.

The opposite longitudinal edges of the saw blades 1, 2, i.e. their back edges, are guided to be slidable in a guide rail 4 which extends the full length of the saw blades. The guide rail 4 comprises two co-operating rebated backing strips 5 whose rebates define the guide groove in which guide flanges 6 which are formed at the back edges of the saw blades 1, 2 by appropriate thinning down of the blades are mounted for sliding movement. An anti-friction film or sheet 7, for example of tetrafluoroethylene, is provided between the two saw blades 1 and 2.

The two rebated backing strips 5 are held together by screws or rivets 8. Adjacent to the end remote from the driven end each of the rebated backing strips 5 is provided, within the region of the rebate, with a pin 10, preferably a pin screwed into place, which is arranged to extend through an elongate slot 9 in the guide flange 6 of the respective saw blade 1 , 2 and in combination with this slot, form a releasable slot-pin coupling. This holds the saw blades 1, 2 on the guide rail 4 so that they cannot become lost.

The mutual holding together of the two saw blades 1, 2 is ensured by the provision of pins 12 in the one saw blade 1 and elongate slots 11 in the other saw blade 2 which extend in the longitudinal direction of the saw blade. The slots 1 1 are longer than the working stroke of the two saw blades 1, 2 and at one end of each slot the slot is enlarged to form a generally circular hole 1 a having a diameter equal to the diameter of the head of the associated pin 1 2. A releasable slotpin coupling is thereby again created.

At its end adjacent to the driving means the guide rail 4 is provided with holes 13 which permit connection to the motor drive, and in particular to its housing. The saw blades 1, 2 are provided with holes 14 at their driven ends for connection to the motor drive. This can be the conventional type of connection used with motorised hedge clippers.

The motorised saw can alternatively be provided with a quick-action coupling, which as shown in Figs. 6 and 7, comprises, in the usual way, short sliders 17 connected to the motor drive and which have recesses 16 in their upper edges into which the ends of the saw blades 1 and 2 equipped with appropriately shaped arcuate projections 15 engage in a positive manner. This coupling holds the parts together, is enclosed by a sliding sleeve 18, and is held in place by a screw 19.

Since the guide rail inclusive of its outer faces is flush with the outer faces of the saw blades 1 and 2, it represents no hindrance when sawing relatively thick pieces of wood or tree trunks. In order to be able to guide and press the saw safely when carrying out such work, the guide rail 4 is provided with a hand-grip 20 which is preferably removable by being unscrewed and which is positioned at an appropriate distance from the motor drive housing 21.

Claims (9)

1. A motorised saw comprising a motor drive portion mounted within a housing which has a handgrip, and two reciprocatingly driven saw blades with teeth set to project out beyond the blade faces and arranged to move in opposed directions, in which the saw blades are releasably connected to the motor drive portion, in which the back edges of the saw blades are guided in a guide rail fixedly connected to the housing and extending over the whole length of the saw blades thereby to hold the saw blades in mutual sliding contact, and in which the width dimension of the guide rail lies within the saw tooth profile.

2. A motorised saw according to claim 1, in which the saw blades are each provided along their longitudinal back edges with a guide flange of about half the width of the respective saw blade, in which in the blade region between the guide flanges and teeth the blades are held together along the blade length by a plurality of slot-pin connections, the pins being fixedly connected to the faces of the saw blades, in which the guide flanges are slidingly received in a common closed groove defined by two mirrorsymmetrically formed rebated backing strips which together form the guide rail, and in which the saw blades at the ends remote from the driving means are held in said groove by means of a slot-pin coupling extending through both saw blade guide flanges and both backing strips, and in which the outer faces of the backing strips and the heads of the pins of the slot-pin coupling are flush with the outer faces of the two saw blades.

3. A motorised saw according to claim 2, in which the slot-pin connections between the two saw blades comprise pins riveted into one saw blade and slots provided in the other saw blade, wherein the slots are longer than the blade stroke and are provided with a hole enlarged to the diameter of the pin head at at least that end of each slot nearer the driven end of the blades.

4. A motorised saw according to claim 2, in which the slot-pin coupling between the saw blades and the rebated backing strips which constitute the guide rail comprises slots provided in the guide flanges of the saw blades and pins extending from the backing strips.

5. A motorised saw according to any preceding claim, which includes an anti-friction film or layer, for example of tetrafluoroethylene, between the saw blades.

6. A motorised saw according to any preceding claim, in which the guide rail is provided with a hand-grip.

7. A motorised saw according to any preceding claim, which includes a quick-action coupling at the motor end of the saw blades, said coupling comprising two short sliders connected to the motor drive and each including a recess in their upper edge on the saw blade side into which a projection on the driven end of the saw blades is engageable in a positive manner, a sleeve slidable over the sliders and the driven ends of the saw blades to enclose the same, and screw means to hold the sleeve in place.

8. A motorised saw according to any preceding claim, in which the guide rail is screwed to the housing of the motor drive.

9. A motorised saw substantially as hereinbefore described with reference to the accompanying drawings.