GB2252072A - Jigsaw - Google Patents

Abstract

A jigsaw in which an elongate blade carrier reciprocates longitudinally and transversely to follow a single arcuate path common to both longitudinal half-cycles, has a cam follower (3) which is stationary during operation of the jigsaw and causes the transverse reciprocations. The blade carrier (118) has an arcuate cam surface (182) formed along part of its longitudinal surface, the stationary cam follower lies adjacent the cam surface of the blade carrier, and resilient biasing means (7) urges the blade carrier into engagement of its cam surface with the cam follower. <IMAGE>

Description

JIGSAW The invention relates to a jigsaw having a pendulum mechanism to produce a transverse component to the feed movement of the essentially vertically reciprocating saw-blade. Such pendulum mechanisms have the effect of increasing the cutting speed.

West German Patent Specification No. 2235862 discloses a jigsaw of this type, in which the saw-blade is connected to a blade carrier driven into vertical reciprocation by an eccentric cam on a gear on a drive shaft.

A lever pivoted at its upper end engages the lower end of the blade carrier and swings with a pendulum motion, causing the desired transverse reciprocating movement in the blade carrier. The pendulum motion is provided by spring-biasing the lever against an annular cam surface on a cam disc rotated by the drive shaft.

A similar effect is achieved in the jigsaw disclosed in our West German Patent Application No.3408847, except that in this case a pendulum lever acts directly on the saw-blade, by way of a roller bearing.

U.S. Patent Specification 2946358 also discloses the direct action of a transverse reciprocation mechanism on the saw-blade, in this case achieved by providing a cam surface on the blade edge, consisting of a rhombus-shaped lateral extension of the blade at its upper end near its mounting on the blade carrier. The blade path is along a single arc, unlike a pendulum bob, i.e. the path during the cutting stroke is simply retraced during the non-cutting stroke. Selection of different blades with different cam surfaces allow the stroke and phase to be altered to suit the material being worked.

It is an object of the present invention to provide a pendulum effect in a very simple manner, so that a jigsaw can be manufactured at a lower cost than hitherto, and without the need to provide special blades.

Accordingly, the invention provides a jigsaw in which an elongate blade carrier reciprocates longitudinally and transversely to follow a single arcuate path common to both longitudinal half-cycles, the jigsaw having a cam follower which is stationary during operation of the jigsaw and causes the transverse reciprocations, wherein the blade carrier has an arcuate cam surface formed along part of its longitudinal surface, the stationary cam follower lies adjacent the cam surface of the blade carrier, and resilient biasing means urges the blade carrier into engagement of its cam surface with the cam follower.

The invention exploits the relative simplicity of the type of drive in which the forward stroke follows the same arcuate path as the return stroke, but without the need for non-standard blades. The particular arrangement of the invention allows for greater integration of the component parts of a jigsaw, which enables it to be manufactured at a lower cost.

Preferably, the blade carrier comprises a rod supported at its upper end in a bearing and coupled to a drive mechanism for longitudinal reciprocation, and a fixed arrangement is provided for guiding a lower portion of the rod, the cam follower and the resilient biasing means being connected to the guiding arrangement to form an integrated assembly.

Conveniently, the transverse position of the cam follower, and thus the amplitude of the transverse reciprocations, is adjustable by a manual control on the jigsaw. In this context, the cam follower preferably comprises a roller journalled eccentrically on a transverse shaft rotatably driven from the manual control, such that manual rotation of the control varies the transverse position of the axis of the roller. For particular simplicity and low cost, it is advantageous that the shaft and the manual control form part of the aforesaid integrated assembly.

The blade carrier, referred to as the lifting rod in the example described below, may have any generally elongate configuration, and the cam surface may project transversely from its longitudinal surface, but it is preferred that the cam surface is indented in an otherwise generally flat longitudinal surface of the blade carrier.

An electrically powered jigsaw embodying the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of the jigsaw shown with a blade connected; Figure 2 is a section, taken longitudinally through the blade carrier (lifting rod), on an enlarged scale, and as viewed from one side, through the front portion of the jigsaw of Figure 1; and Figure 3 is a section, taken longitudinally through the lifting rod, to the same scale as Figure 2, and as viewed from the front, through part of the jigsaw of Figures 1 and 2.

The electrically-powered, hand-held jigsaw shown in the drawings has a conventional housing 31, which forms a handle 34, into which an on/off switch 33 projects. On the under-side of the housing 31, a shoe 35 is mounted which, at its front end (left-hand side in Figures 1 and 2) has an open-ended slot for the vertically reciprocating saw-blade 36. The region around the slot is shielded above the shoe 35 by a protective guard 38 of transparent material which is shown only in Figure 1.

The jigsaw is driven by an electric motor, not shown, mounted in the housing 31. The armature shaft 10 (Figure 2) of the motor is mounted inboard its outer end in a bearing 11 and has a pinion 12 on its outer end, which pinion engages a gear wheel 13 mounted rotatably on a shaft 14 by means of bearings. On the gear wheel 13 an eccentric projection 23 is formed, on the end of which an eccentric disc 15 is fastened, so that it rotates together with the gear wheel 13 on the shaft 14.The eccentric disc 15 carries an eccentric pin 16 arranged eccentrically to the shaft 14, on which pin a follower roller 17 is rotatably mounted which is in engagement with a cross slot 181 in a lifting rod 18, so that, in a known manner, on rotation of the eccentric disc 15 and with the consequential rotary movement of the eccentric pin 16, the lifting rod 18 is reciprocated vertically while the roller 17 reciprocates in the cross slot 181 of the connecting rod 18.

The connecting rod 18 is guided with its upper end in a rotary bearing 19 and with a region lying below the cross slot in a bearing arrangement 20, 21. The bearing arrangement has a guide 20 with an enlarged through-opening 201 and a plastics guide 21, which can be reciprocated horizontally. On the lower end of the lifting rod 18 there is a saw-blade clamp 22 in which the saw-blade 16 is clamped.

A counterbalance weight 24 is mounted rotatably on the eccentric projection 23 of the gear wheel 13. The weight 24 has an upper slot 26 into which a guide pin 28 extends, fixed in the housing 11. As a result of the eccentric mounting of the counterbalance 24 on the eccentric pin 23 and its being unable to rotate as a result of the engagement of the guide pin 28 in the slot 26, the counterbalance weight 24 is reciprocated vertically (Figure 2) in the opposite direction to that of the eccentric pin 16. This counterbalances the eccentric pin 16 as it rotates around the shaft 14.

An air duct 43 is formed in the housing 31, through which air issues from a ventilator fan of the electric motor so as to blow away saw-dust from the working area.

A transverse reciprocation and adjustment mechanism 1, 3, 4, 5, 6 is supported by the bearing arrangement 20, to form an integrated assembly, which is a compact structural unit. A cam-following, cylindrical roller 3 is mounted eccentrically for rotation on a reduced diameter position of a shaft 4, whose fixed axis is transverse to the longitudinal direction of the lifting rod 18. The roller 3 thus rotates about a spaced, parallel axis. An end portion of the shaft 4 projects from the bearing arrangement 20, and is splined for rotary driving coupling to a manual control lever 6. An indexing ring 1 is fixed to the opposite end of the shaft 4, and has an annular indexing surface 101 which engages a corresponding surface on the bearing arrangement 20.A compression spring 5 mounted over the end portion of the shaft 4 bears at one end against lever 6 and at the other end against the other side of the bearing arrangement 20, so that it urges the indexing ring 1 against the bearing arrangement 20. The indexing surface 101 defines four angularly-spaced stable positions of the shaft 4, and the corresponding positions 0-1-2-3 of the end of the lever 6 are marked on a portion 42 (Figure 1) of the housing 11.

At position 0, as shown in Figure 2, the axis of the roller 3 is at its furthest right, away from the lifting rod 18. The roller 3 surface is then flush with a flat longitudinal surface of the lifting rod 18.

A smooth indentation 182 (Figures 2 and 3) formed in the lifting rod 18 over a length corresponding to the amplitude of its longitudinal reciprocations. The indentation is essentially an inclined plane joined smoothly with a part-cylindrical surface at its upper portion. The planar portion of the indentation is inclined at about 200 to the longitudinal axis. The tangent to the upper edge of the indentation is inclined at about 450 to the axis, so that it is substantially sharper than the lower edge. The greatest depth of the indentation, occurring at about a third of the way down its length, is similar to the difference between the extreme transverse positions of the roller 3 surface as it rotates eccentrically about the axis of the shaft 4, through about 900 between angular positions 0 and 3.This difference is approximately equal to the distance between the shaft 4 axis and the roller 3 axis.

The lifting rod 18 is spring-biased transversely towards the rear of the jigsaw, to the right in Figure 2, and is thus urged into engagement with the rear edge of the opening 201 through the guide 20, by means of a spring element 7 mounted within the bearing arrangement 20.

Depending upon the extent to which the roller 3 surface projects transversely beyond the rear edge of the opening 201 (the right-hand edge in Figure 2), the lifting rod 18 will be cammed by virtue of the cam-following roller 3 rolling along the cam surface defined by the indentation 182 against which it is urged by the spring element 7.

At the position 0 shown in Figure 2, the roller surface does not project at all beyond the edge of the opening 201, and the blade is caused to reciprocate longitudinally with no transverse component. At the position 3, with the shaft 4 rotated through about 900, the roller surface engages the cam surface 182 at its deepest point when the flat longitudinal surface of the lifting rod 18 engages the right-hand edge of the guide opening 201, causing the lifting rod to be cammed transversely (to the left in Figure 2) when it rises. The transverse reciprocating movement which results is in phase with the longitudinal reciprocations, and its amplitude depends on the extent of the projection of the roller surface. The forward stroke and the return stroke cause the lifting rod, and thus the blade 16, to follow the same, arcuate path.

The transverse reciprocation is allowed by virtue of the rotary bearing 19, and the freedom of sliding movement of the follower roller 17 axially of the pin 16 in the cross slot 181.

At positions 1 and 2, intermediate the extreme positions, the roller surface projects beyond the edge of the guide opening 201 by amounts less than the greatest depth of the cam surface 182, so that the camming action commences later and ceases earlier in the cycle of longitudinal reciprocation, and the transverse amplitude is also less.

The plastics guide 21 slides freely and follows the transverse reciprocations.

The jigsaw has been found to cut 38mm chipboard nearly three times faster at the setting "3 " (maximum) than at the setting "0" (minimum) for transverse reciprocation.

Claims (8)

1. A jigsaw in which an elongate blade carrier reciprocates longitudinally and transversely to follow a single arcuate path common to both longitudinal half-cycles, and the jigsaw having a cam follower which is stationary during operation of the jigsaw and causes the transverse reciprocations, wherein the blade carrier has an arcuate cam surface formed along part of its longitudinal surface, the stationary cam follower lies adjacent the cam surface of the blade carrier, and resilient biasing means urges the blade carrier into engagement of its cam surface with the cam follower.

2. A jigsaw according to Claim 1, in which the blade carrier comprises a rod supported at its upper end in a bearing and coupled to a drive mechanism for longitudinal reciprocation, and a fixed arrangement for guiding a lower portion of the rod, the cam follower and the resilient biasing means being connected to the guiding arrangement to form an integrated assembly.

3. A jigsaw according to Claim 1 or 2, in which the transverse position of the cam follower, and thus the amplitude of the transverse reciprocations, is adjustable by a manual control on the jigsaw.

4. A jigsaw according to Claim 3, in which the cam follower comprises a roller journalled eccentrically on a transverse shaft rotatably driven from the manual control, such that manual rotation of the control varies the transverse position of the axis of the roller.

5. A jigsaw according to Claim 4, in which the shaft and the manual control form part of the integrated assembly.

6. A jigsaw according to any preceding claim, in which the cam surface is an indentation in a longitudinal surface of the blade carrier.

7. A jigsaw according to any preceding claim, having a blade coupled to the lower end of the elongate blade carrier.

8. A jigsaw substantially as hereinbefore described herein with reference to and as illustrated by the accompanying drawings.