GB2071009A - A saw - Google Patents

Abstract

A rotatable portable saw has a saw blade 2 which is mounted with respect to carrier plate 15 so that the position of the blade relative to the plate 15 can be angled slightly relative to the direction of traverse of the saw as determined by straight edge 50 of planar base 17 so that the width of the cut can be made slightly greater than the width of the blade. This is achieved by pivoting brackets 12, 11 carrying the saw about pivot 78 by means of an eccentric 76 by way of a lever 70 and Bowden cable 80. <IMAGE>

Description

SPECIFICATION A saw The present invention relates to a saw having a rotatable saw blade, and particularly to such a saw which, in operation, is moved across a workpiece to effect a cut.

With saws of this type, the saw blade tends to splinter the wood, at the point at which it emerges from the wooden workpiece being sawn, causing an unclean cut. This splintering occurs with even the most expensive tungsten carbide saw blades. A comparable problem arises particularly with coated materials such as melamine-coated chipboard, the coating being very prone to chipping by the emerging saw blade at the saw cut. Once chipped, it has an unsightly appearance which cannot satisfactorily be concealed.

To deal with this problem, I have already proposed in my patent application No. 8030021 (from which this present application is divided) a saw comprising a planar base, a rotatable saw blade pivotally mounted with respect to the base so that the axis of rotation of the blade is parallel to the pivotal axis and so that the cutting edge of the blade may depend below the plane of the base, and latch means enabling the saw blade to be fixed in a pivoted position relative to the base.

With the saw according to that proposal, it is possible to eliminate the problem by firstly making an initial cut of depth less than the thickness of the workpiece, in a first traverse of the saw, and thereafter, in a second traverse, cutting right through the workpiece along the line of the initial cut.

Provision is madeforthe possibility that the initial cut should be of width greater than the thickness of the saw, and this is achieved by the angular position of the saw blade being variable relative to the base.

The present invention is based upon the appreciation that the need for production of saw cuts of width greater than the thickness of the saw blade is not confined to the initial cut in a workpiece cutting operation as just described.

Pursuant hereto, the present invention provides a saw comprising a rotatable saw blade so mounted relative to a planar base as its project below the plane of said base whereby cutting can be achieved by traverse of the saw across a workpiece with an edge of the base guided by a fence, characterised in that the mounting includes means enabling the angle of the saw blade relative to said edge of the base to be varied to enable the saw blade to produce a cut which is wider than the thickness of the saw blade.

In order that the invention may be more clearly understood, it will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view illustrating a portable circular saw conforming to the present invention; Figure 2 is a partial view of the saw of Figure 1, showing a constructional detail; Figure 3 is a further partial view of a saw of Figure 1 showing a further constructional detail; Figures 4a and 4b diagrammatically illustrate the operation of the saw; Figure 5 is an enlarged detail view of the mounting arrangement of the saw of Figures 1 to 3, and Figure 6 is an exaggerated cross-sectional view illustrating a type of saw cut obtained with the illustrated saw.

The illustrated saw comprises an electric driving motor 1 operative to rotate a circular saw blade 2 disposed partially in a safety housing 3. The motor 1 and safety housing 3 are disposed on opposite sides respectively of a central body 4 moulded of plastics material in the form of a handle 5. The handle 5 incorporates a power on/off switch 6, a neon power on/off indicator 7 and a latch 6a, which enables the switch 6 to be temporarily held in its "on" condition.

An electrical power lead to the saw is shown at 8.

The central body 4 has a metal mounting plate 9 connected to it by screws 10. This plate 9 is, in turn, connected to an inverted U-shaped bracket 11 which is pivotally connected to a shallow further U-shaped bracket 12. The pivotal connection is by means of a rod 13 extending through aligned apertures in the legs of the two brackets 11 and 12. The bracket 12 is loosely bolted by bolts 14to a carrier plate 15. These bolts 14 extend through slots in the base of the bracket 12 which bracket 12 is pivotally connected to the carrier plate 15 on or near the centre line of the saw blade 2, by pivot 78, thus allowing the angular position of the bracket, and therefore the blade 2, to be adjusted with regard to the carrier plate 15.The carrier plate 15 is pivotally connected to a bottom plate 16, the two plates 15 and 16 together forming a base, indicated generally by the reference numeral 17 of which the bottom plate 16 is planar, of the saw.

To provide the pivotal connection between the plates 15 and 16, upstanding apertured lugs 18 are provided on the bottom plate 16 and outwardlyextending apertured lugs 19 are provided on the carrier plate 15. Pivots 20 extend through the aligned apertures. With this arrangement, when it is desired to make a cut with the saw blade 2 angled relative to the vertical, the carrier plate 15 may be fixed in a chosen pivotal position relative to the bottom plate 16 by means of a backing slide device 100.

A helical compression spring 21 acts between an L-shaped bracket 22 connected to the base of the bracket 11 and a locating cup 23 fixed to the plate 15.

Referring specifically to Figure 2, apart from its pivotal connection as provided by the brackets 11 and 12, as just described, the central body 4 of the saw is also connected to the carrier plate 15 of the saw base 17 through a latching device indicated generally in Figure 2 by the reference numeral 30.

This latching device 30 comprises a curved Ushaped bracket 31 with two feet 32, at the free ends of the legs of the U, fixed by screws or rivets 33 to the carrier plate 15. One of the legs of the U is slotted at 34, and a bolt 35 extends through this slot and a threaded lever 45 and bracket 37 forming a pivot and is retained therein by a lock nut 36. The bracket 37 is apertured and a latch member 38 is pivotally connected to it by means of a bolt 39 and wing nut 40.

The bolt 39 also extends through the handle 4 to connect it to the latch member 38. A spring 41 surrounds the bolt 39 and it constrained to urge the latch member 38 and the bracket 31 together. The tongue of the latch member 38 has three apertures 42 and the bracket 31 has a complementary projection 43 so that the body 4 of the saw, and therefore the saw blade 2, can be held latched in one of three pivoted positions relative to the saw base 17. The blade positions corresponding to the two uppermost apertures 42 are first and second operative blade positions and the blade position corresponding to the third aperture 42 is a safety position with the blade 2 within the housing 3. Movement of the lever 45 from the position shown in Figure 3 to that shown in Figure 2 locks the bracket 31 relative to the bracket 37.The safety housing 3 also acts as a sawdust collector, the dust being removed by vacuum through the outlet 47.

Turning now to Figure 5 of the drawings, since the bolts 14 extend through slots in the base of the bracket 12 they allow the position of the bracket to be adjusted with regard to the carrier plate 15 between two angular positions about the pivot 78 which lies on or near the centre line of the saw blade 2. A mechanism is associated with the bracket 12 for automatically pivoting the bracket 12 about the pivot 78, depending upon the position of the saw itself.

This mechanism comprises an eccentric 76 disposed in an aperture cut into the bracket 12 which eccentric is pivoted positively to the carrier plate 15 and connected to a lever 70. The lever 70 is connected by a connecting rod 73 and a swinging arm 72 to a pivoted stop member 74. The arm 72 and rod 73 are pivotally connected together at 75 and the other end of the arm 72 is pivotally anchored to the stop member 74. A compression spring 71 acts between the free end of the lever 70 and one leg of the bracket 12. A striker 77 is adjustably fixed to the underside of the U-shaped bracket 11. The connecting rod 73 is joined via a Bowden cable 80 to an actuating lever 81 pivotally mounted on the body 4 of the saw. The operation of this mechanism will be described later.

The operation of the saw will now be described firstly with reference to Figures 4a and 4b of the drawings. A cut right through a workpiece is effected by means of a double traverse of the saw over the workpiece. With the saw blade 2 latched in its first operative position, that is with the projection 43 engaged with the middle aperture 42 of the latch member 38, the workpiece is traversed from right to left by the saw as shown in Figure 4a. The saw blade 2 revolves anti-clockwise and the teeth of the saw blade 2 therefore aproach the surface of the workpiece at the point of cutting C. The depth of the saw blade 2 below the surface of the material of the workpiece is less than the thickness of the material and is preferably about 1 to 2 mm. The first traverse therefore does not result in the material being cut right through, but only to a depth indicated say by the line L.At the end of the first traverse the latch member 38 is released to allow the saw blade 2 to pivot downwards, the member 38 being automatically relatched in the lower position where the projection 43 will extend through the upper aperture 42. Release is effected by pulling the member 38 with the index finger against the spring force provided by the spring 41. The workpiece is then traversed from left to right as shown in Figure 4b.

The direction of rotation of the saw blade 2 remains the same so the teeth of the blade 2 again approach the surface of the material at the point of cut C but this time from below. With this second traverse the material is cut right through. To ensure that both traverses take place along the same line, a straight edge, provided by edge 50 of the base 17, is run along a fixed straight edge (not shown).

Turning now to Figures 5 and 6 of the drawings, the adjustment mechanism for the bracket 12 is adjusted manually to the position shown in full lines in Figure 5. In that full line position the pivot 75 is above the line joining the ends of the arm 72 and the connecting rod 73 and is urged upwardly by the spring 71. This manual adjustment is obtained by depressing the actuating lever 81 to pull the Bowden cable 80, and through it the lever 73, upwardly. The lever 70, with the eccentric 76, is pivoted clockwise thus angling the bracket 12 and the saw blade 2 indirectly supported on it slightly relative to the straight edge of the plate 15. Accordingly, as the blade 2 is advanced through the material during the first traverse, a cut is produced which is slightly greater in width than the kerf width of the saw blade 2.A suitable angling will give, for example, a width of cut .010" wider than the width of the blade. The saw blade 2 revolves anticlockwise and the teeth of the saw blade therefore approach the surface of the material at the point of cutting C. The depth of the saw blade 2 below the surface of the material is made very small to avoid undue loading of the saw due to the slight angling of the blade 2 to the direction of traverse. A depth of 1 mm would be considered sufficient. At the end of this first traverse, therefore, a cut 1 mm deep and slightly wider than the saw blade 2 has been cut. The base of the cut is indicated at L in Figures 4a and 4b and 6. In setting up the saw for cutting, the position of a striker 77, the parallel portion of the saw blade 2, and the degree of offset of the saw blade 2 when angled, can be adjusted by means of respective adjusting nuts 90, 91 and 92.

As already described, at the end of the first traverse, the latch member 38 is released to allow the saw blade 2 to pivot downwards, the member 38 being automatically relatched in the lower position where the projection 43 will extend through the upper aperture 42. Release is effected by pulling the member 38 with the index finger against the spring force provided by the spring 41. The lowering of the saw blade 2 automatically adjusts the mechanism for pivoting the bracket 12 about the pivot 78. On lowering of the saw blade 2, the striker 77 depresses the pivot 75 and once this pivot 75 has moved down past the position in which the arm 72 and rod 73 are aligned, the lever 70 snaps sharply to the left under the action of the spring 71. The positions then adopted by the lever 70, the arm 72 and the rod 73 are shown in dotted lines in Figure 6. In that position the saw blade 2 is aligned parallel with the straight edge 50 of the plate 15. The workpiece is then traversed from left to right as shown in Figure4b.

The direction of rotation of the saw blade 2 remains the same so the teeth of the blade 2 again approach the surface of the material at the point of cut C but this time from below. With this second traverse the material is cut right through, and when the operator lifts the saw from the workpiece the body 4 of the saw moves automatically away from the carrier plate 15 with the help of the compression spring 21 thus ensuring that the blade 2 is fully and safely retracted into its housing 3.

To make this automatic separation possible, the projection 43 and its locating apertures 42 are shaped in such a way that they slide out of engagement on the lifting movement, and correspondingly on the downward movement they engage positively in the manner of a ratchet.

The form of the composite slot produced in the workpiece is shown in cross-section in Figure 6. If desired, the angle of cut can be adjusted by pivoting the upper plate 15 relative to the lower plate 16 of the base.

The above described portable saw may simply be used to prevent the sort of splintering of workpieces normally sustained at the point where the rotating saw blade emerges from the material of the workpiece. By providing in the saw the means whereby the saw blade always approaches the surface of the material is pushed in rather than out during the cutting operation. In addition, in the major cutting stroke, which is the second traverse, the blade 2 emerges into a wider already cut groove and the danger of splintering is thereby reduced or eliminated. The saw has great applicability to the sawing of melamine-faced or similar coated wood, ply-wood, chipboard or other types of board since with this type of faced material the emerging saw blade usually causes unsightly chipping of the facing material.A portable saw has been described because it is felt that the greatest advantages of the invention will be secured with this sort of saw.

However, the invention is equally applicable to a fixed saw. With such a saw it would of course usually be necessary to move the workpiece relative to the saw blade rather than the other way round. The saw has therefore been designed to fit into a workbench in an orthodox manner. The workpiece is moved across the saw blade for a first, scribing cut and after pivoting the blade upwards through a base plate the workpiece is moved back again thus cutting it right through.

It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention as defined by the claims. For example, in the illustrated embodiment, instead of a lever mechanism for rotating the bracket 12 with respect to the plate 15, the bracket 12 could be directly rotated. Alternatively, this rotation could be effected through a Bowden cable controlled directly from the handle of the saw. In both cases, however, automatic return of the saw blade to the aligned position should be provided for to reduce the danger of the blade being drawn at an angle through too great a thickness of material. By providing more stop positions (e.g. 1/8" holes at 1" intervals) on the member 38, different sizes of saw blade (e.g.

5",6" and 7") can be accommodated. In addition the projection 43 may be adjustable so that wear on the blade caused by sharpening can be taken up. The member 38 could be made interchangeable for different operations. One such member could have a plurality of stop positions as close together as possible. Alternatively a fine toothed ratchet could be used.

In another variation, a simple alternative to the Bowden cable operated eccentric 76 is a manually operated lever directly connected to the eccentric and positioned in such a way that the saw cannot be lowered whilst the lever is in the scribing position.

Also, instead of having the latch centrally of the handle it could be positioned otherwise for example to one side of the handle. Further by making the position of the stop of the latch adjustable and increasing the number of apertures a virtual continuous adjustment can be provided for.

Claims (6)

1. A saw comprising a rotatable saw blade so mounted relative to a planar base as its project below the plane of said base whereby cutting can be achieved by traverse of the saw across a workpiece with an edge of the base guided by a fence, characterised in that the mounting includes means enabling the angle of the saw blade relative to said edge of the base to be varied to enable the saw blade to produce a cut which is wider than the thickness of the saw blade.

2. A saw as claimed in claim 1 wherein the mounting means comprises a bracket pivotally mounted on the base.

3. A saw as claimed in claim 2 wherein pivotal movement of the bracket relative to the base is achieved by means of an eccentric spaced away from the pivot axis of the mounting of the bracket on the base.

4. A saw as claimed in claim 1,2 or 3 wherein the saw includes an electric motor which drives the blade.

5. A saw as claimed in claim 4 wherein the saw is a portable saw and includes a handle enabling it to be traversed manually.

6. A saw substantially as hereinbefore described with reference to and as illustrated in the accom panying drawings,