GB2158770A

GB2158770A - Power saw

Info

Publication number: GB2158770A
Application number: GB08509635A
Authority: GB
Inventors: Jeffrey Berman
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-04-13
Filing date: 1985-04-15
Publication date: 1985-11-20
Also published as: GB8509635D0

Abstract

A power saw has a pair of saw blades (17A, 17B) which are driven in anti phase reciprocation by a drive transmission (12, 13) connected to both blades and driven by, for example, an electric motor (10). The two saw blades cut independently in two parallel planes. <IMAGE>

Description

SPECIFICATION Power saws This invention relates to power saws.

A known type of power saw, which is normally designed as an attachment for a power drill, has a reciprocating blade which projects cantilever fashion from a casing. The precision and ease with which such power saws can be used is adversely affected by the reaction exerted upon the blade upon the work being cut and hence necessitates the use of a fixed sole plate reaction member. An object of the present invention is to provide an improved power saw, by virtue of greater ease of handling in use.

The present invention provides a power saw having two blades arranged side by side in parallel planes and driven in anti-phase reciprocation by a drive transmission connected to both blades. The blade material, shape and tooth profile is selected to suit the materials to be cut.

Because the two saw blades reciprocate in antiphase relation the cutting reaction forces exerted upon the two blades tend to cancel each other.

This contrasts with a single-blade power saw, which relies on the use of a fixed sole plate to provide reaction to the cutting force.

Each of the two reciprocating blades of the power saw has an independent sawing action, and for this purpose each saw blade has a saw tooth cutting edge with a profile dictated by the material and sawing function to be performed - for example, a cross-cut or rip-sawing tooth profile. There is no shearing interaction between the two saw blades, although the two saw blades may be in sliding contact with each other.

The two saw blades may have teeth the set of which is such that, in operation, the reaction of the work on the teeth forces the blades towards each other. Moreover, the two blades may be provided with or interact with mechanical guide-stops which prevent the blades moving apart and guide them for parallel reciprocating movement. Thus the two saw blades can act as mutual guides, bracing each other against flexing.

Preferably the saw blades are such that the natural tooth reaction forces are constrained to ensure parallel movement of the two blades. The teeth of the two saw blades are ground and set in a manner according to the nature of the work to be sawn. In order to promote the removal of sawn debris the saw blades may be provided with deep cut saw teeth interspersed at intervals along their cutting edges.

One embodiment of the invention utilises blades with a cross-sectional profile which may form a channel or channels between the two blades to facilitate the removel of debris.

The two saw blades may be maintained at a constant separation by sliding contact between two guide surfaces spaced from the cutting edges of the blades. For example, the two guide surfaces may be formed by lateral projections on the blades themselves. Alternatively the blades may be in close sliding contact and inter-blade friction may be minimized by a lubricant film or coating.

In one practical embodiment of the invention the two blades project cantilever-fashion from a casing which houses the drive transmission. The saw blades may be located at one side of the casing, to facilitate sawing of work close to walls or other obstructions. The drive transmission may be so arranged that the saw blades can be coupled to the drive transmission on either side of the casing, to facilitate the cutting of work close to obstruction either on the left or on the right of the saw.

The invention may be embodied in a power saw having a self-contained drive motor connected to the drive transmission within the casing. The drive motor may be, for example, an electric motor, an internal combustion engine or an air motor. Alternatively, the casing may be adapted to be fitted as an attachment to a power drill so as to couple the drive transmission to the drive motor of the drill.

Each blade is preferably connected at one end to a reciprocating drive member such as a rod which is driven by the transmission. At least one reciprocating guide may also be connected to the said one end of the blade, the guide being spaced from and parallel to the drive member, to prevent rotation of the blade about its connection to the drive member. Alternatively the torsional rigidity may be achieved by a single composite reciprocating drive member.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cut away side elevational view of a power saw according to one embodiment of the invention; Figure 2 is a sectional plan view of the power saw, taken on the line ll-ll of Figure 1; Figures 3 and 4 are partial elevational views showing two alternative saw tooth profiles for the blades of the power saw; Figures 5 and 6 are cross sectional views of two alternative pairs of saw blades for use in the power saw according to the invention; Figure 7 is an elevational view of part of the saw, illustrating one form of mechanical guide-stop between the two saw blades; Figure 8 is a cross sectional view on line VIII-VIII in Figure 7;; Figure 9 is an elevational view of part of the saw, similar to Figure 7, illustrating an alternative form of mechanical guide-stop between the two saw blades; Figure 10 is a cross sectional view on line X-X in Figure 9, and Figure 11 is a cross sectional view corresponding to Figure 10, illustrating a further alternative form of guide-stop interconnection between the two saw blades of the saw.

Referring first to Figures 1 and 2, the illustrated power saw according to the invention has a handheld casing 1 of metal or plastics housing an electric drive motor 10 driven via a power lead from mains or portable sources (not shown). Operation of the motor 10 is controlled by a switch or alter natively a progressive speed control 11 conveniently located in a handgrip 2 forming part of the casing 1.

The motor 10 is connected through a reduction gear train 12 to a crank shaft 13 which carries two cranks 13A, 13B arranged at 1800 relative to each other. The two cranks 13A, 13B are drivingly connected by respective connecting rods 14A, 14B to respective drive rods 15A, 15B arranged side by side and parallel to each other for sliding movement in respective bores formed in the casing 1.

Externally of the casing 1 the two drive rods 15A, 15B are connected by removable pins 16A, 16B to respective reciprocating saw blades 17A, 17B. The pins 16A, 16B may take the form of bolts, linch pins, grub screws or other connector elements such that the blades 17 can conveniently be connected to or disconnected from the drive rods 15.

In order to prevent undesirable pivoting of the saw blades 17 about their connecting pins 16 each saw blade 17 may also be connected to a reciprocating guide in the form of a slave rod 18 which is similar to the drive rod 15 of the saw blade and spaced from the drive rod for sliding movement in a parallel bore. Each slave rod 18A, 18B is connected to the respective saw blade 17A, 17B by a further connecting pin 19A, 19B.

As well as ensuring torsional rigidity of each saw blade 17A, 17B, the two guide or slave pistons 18 also relieve the load on the bearing sleeves of the drive rods 15A, 15B in use of the saw.

The gear train 12, the crank shaft 13 and the rods 15 and 18 may be contained in plastics or metal housings for lubrication by internal oil or packed grease. Alternatively, the moving parts of the saw may be lubricated additionally, or exclusively, by the external application of lubricants, with the provision of suitable seals to prevent the ingress of dirt or grease into the drive motor 10.

The gear train 12 may be fabricated in metal, nylon, or other suitable materials.

The shape, size, number and set of the saw teeth of the two saw blades 17A, 178 is chosen according to the nature of the work to be cut. Two examples of saw tooth profiles are illustrated in Figures 3 and 4. In practice deep cut saw teeth such as those of Figure 4 may be interspersed at intervals with the smaller saw teeth of Figure 3, to facilitate the removal of debris from the saw teeth. Saw blades 17 of different saw tooth profile may be readily interchanged by virtue of the removable connector pins 16, 19.

A variable speed gear box may be incorporated in the gear train 12 to provide for both speed and power variation. In addition, different stroke lengths of the blades 17 may be provided by having interchangeable drive heads containing different crank shafts for connection to the drive transmission.

The two saw blades 17A, 17B are each provided with ground and set saw teeth, and the set of the saw teeth may be such that, in operation, the two blades 17A, 17B are urged towards each other, thereby preventing "splaying" of the two blades outwards in the sawing process. Figure 5 illustrates by way of example saw tooth profiles for crosscutting in wood and Figure 6 illustrates saw tooth profiles for rip-sawing in wood. The two saw blades 17A, 17B are maintained at a constant separation by sliding contact between guide surfaces 20, 21 which may be formed by integral projections in one or both blades or by spacers between the blades.

In order to prevent separation of the two saw blades in use various mechanical guide-stop arrangements may be employed. Thus as illustrated in Figures 7 and 8, one saw blade 17B may be provided with a guide pin 22 which reciprocates within a key-hole shaped slot 23 in the other saw blade 17A. Alternatively, as illustrated in Figures 9 and 10, one saw blade 178 may be provided with a guide channel 24 at its edge remote from the cutting edge, in which the adjacent edge of the other saw blade 17A slides.

Figure 11 illustrates a further alternative bladeguiding arrangement, in which a fixed channel-section guide 25 is attached to the saw casing and receives the edges of the two saw blades 17A, 17B remote from their cutting edges.

It is envisaged that hard point type case-hardened teeth would be employed to good effect in the saw of the present invention. These teeth maintain their sharpness and shape in use for a considerable period. It is not envisaged that the blades of the power saw would be resharpened, because of the precision saw tooth profiles required: instead it is envisaged that replaceable case-hardened blades would be provided for the saw.

Claims

1. A power saw having two saw blades arranged side by side in parallel planes and driven in antiphase reciprocation by a drive transmission connected to both blades.

2. A power saw according to Claim 1, in which the two saw blades cut independently.

3. A power saw according to Claim 1 or Claim 2, in which the natural tooth reaction forces are constrained to ensure parallel movement of the two blades.

4. A power saw according to any one of Claims 1 to 3, in which a space is defined between the two blades.

5. A power saw according to any one of the preceding claims, in which means are provided to mount interchangeable blades in the saw.

6. A power saw according to any one of the preceding claims, in which the two blades project cantilever-fashion from a casing which houses the drive transmission.

7. A power saw according to Claim 6, in which the saw blades are located at one side of the casing.

8. A power saw according to Claim 6 or Claim 7, in which the casing also houses a drive motor connected to the drive transmission.

9. A power saw according to Claim 6 or Claim 7, in which the casing is adapted to be fitted as an attachment to a power drill so as to couple the drive transmission to the drive motor of the drill.

10. A power saw according to any one of the preceding claims, in which the two blades are provided with or interact with mechanical restraining means which prevent the blades moving apart and guide them for parallel reciprocating movement.

11. A power saw according to any one of the preceding claims, in which each blade is connected at one end to a reciprocating drive member which is driven by the transmission.

12. A power saw according to Claim 11, in which the mechanical connection to the reciprocating members also provides torsional restraint.

13. A power saw substantially as herein described with reference to and as shown in the accompanying drawings.