Pendulum jigsaws

Abstract: Figure 2 shows a jigsaw in which pendulum motion is imparted on the blade (24) (see Figure 1) by a bell crank lever (28) mounting a support wheel (26). The lever (28) is actuated by pin (34) passing through adjustment shaft (36). The pin (34) is actuated by fork lever (42) journalled around circular cam surface (48) and pivoted on axis (44). Cam surface (48) is eccentrically mounted on gear shaft axis (10). Rotational adjustment of shaft (36), which alters the mechanical advantage of fork lever cam surface (52), is effected by pin (60) passing through shaft (36) and pivotally mounted in slide switch (70). Arrangement allows for compact design of saw.

Description: This invention relates to jigsaws and in particular to powered jigsaws which impart an orbital movement to the blade. That is to say, those which advance the blade slightly in the direction of feed during a cutting stroke. Such saws are also referred to as pendulum jigsaws when the advancement of the blade is through a pendulum action. It is desirable in such jigsaws to provide the possibility of adjustment of the pendulum action because blade advancement is not always an advantage when cutting certain materials. One preferred arrangement is described in GB-A-2053795 which is hereby incorporated herein by reference. In this arrangement, the roller supporting the back of the jigsaw blade is mounted on a bell crank lever whose other end is acted on by a pin passing through a shaft. In the region of the pin the bell crank lever is provided with a circular cam profile which lies in the plane of rotation of said shaft and which is centred on the axis of the shaft. The other end of the pin is acted upon by a similar cam profile of a fork lever pivoted about an axis parallel to said shaft. The other end of the fork lever is forked and is journalled about an eccentric circular cam surface formed on a gear driven by the jigsaw motor. The same cam surface also moves a counter-weight to balance the up and down movement of the jigsaw blade and carrier therefor. The jigsaw blade and carrier are reciprocated by said gear. Thus as the motor rotates and the jigsaw carrier and blade are reciprocated, the fork lever is also reciprocated and through its cam surface, the pin and the bell crank lever, the blade is given a reciprocating movement in the feed direction of the saw, as well as its normal reciprocating cutting stroke along its axis. The adjustment of the pendulum action is effected by rotation of the shaft so as to alter the leverage which the fork lever has on the pin between maximum and minimum positions. In GB-A-2053795 the shaft simply extends out of the rear of the housing of the saw and is provided with a knob for manual adjustment. However, because of the need to provide room between the motor housing and the sole plate of the saw in which to accommodate that knob, the saw appears somewhat "top-heavy" and unbalanced. Moreover, it is desirable to provide the saw with vacuum suction means in the region of the knob so that dust created during saving can be removed and collected. It is therefore an object of this invention to provide a jigsaw having the advantages and features of that disclosed in GB-A-2053795 but which does not suffer the aforementioned disadvantages. In accordance with this invention there is provided a saw comprising a housing for a motor which drives a gear having a blade carrier mounted thereon for reciprocation in a first direction, a cam surface formed on said gear on which a fork lever is journalled, the fork lever being pivoted in the housing about a first axis lying perpendicular to said first direction and acting on one end of the drive pin slidably mounted in a shaft rotatably mounted in the housing about a second axis parallel to said first axis, the other end of said drive pin acting on one end of a bell crank lever pivoted in said housing about a third axis perpendicular to said first direction and said first and second axis, the other end of said bell crank lever carrying a support wheel disposed behind and supporting in the direction of feed of the saw a blade carried by said carrier, means biassing said blade against the support wheel, the fork lever, pin and bell crank being arranged such that on rotation of said gear, the support wheel imparts a reciprocating motion, in said direction of feed of the saw, on the saw blade, rotation of said shaft altering the mechanical advantage of the connection between said fork and bell crank levers, said shaft carrying am adjustment pin mounted in a manually actuable slide switch mounted for movement in the housing in the plane of rotation of the shaft. This arrangement moves the manually actuable pendulum adjustment mechanism from behind the housing to the side of the housing of the saw. Consequently a more compact styling and appearance can be given to the saw with the housing being disposed relatively close to the sole plate of the saw. Moreover, room is now made in the region behind the pendulum adjustment mechanism to dispose a passage for a vacuum extraction means opening above and behind the saw blade. Preferably, said switch is mounted in the housing for movement parallel to said first direction along a straight line, means being provided to allow for the change in distance of said switch from said shaft. Preferably said means comprises said adjustment pin being pivoted in said switch and being a sliding fit in a cross-bore in said shaft. Preferably said switch comprises a knob slidably mounted in a rectangular slot in said housing, a carrier mounted on said kmob inside the housing and covering said slot, and spring means mounted on said carrier and being adapted to engage one of several detents to locate said switch in different positions, the carrier having means to pivot said adjustment pin on the carrier. Said means may comprise a bore arranged parallel to said first and second axes when said adjustment pin is a slide fit in the shaft, otherwise it comprises a slot. The invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic section through a jigsaw according to the invention; Figure 2 is a section on the line II-II in Figure 1; Figures 3a and 3b are perspective views of the carrier and spring respectively is shown in more detail in Figures 4 to 6; Figure 4 is a detailed section through the slide switch shown in Figure 2; Figure 5 is a view in the direction of the arrow A in Figure 4; and Figure 6 is a view in the direction of the arrow B in Figure 4. Figure 1 shows a pendulum jigsaw 1 having a housing 2 including a handle 3, which incorporates a switch 4 and a motor 5. The motor 5 has an armature 6 which drives a gear 8 journalled in the housing 2 about an axis 10. A cage 12 is fixed in the housing and mounts a blade carrier 14. Pin 16 transfers rotary motion of the gear 8 about axis 10 into reciprocating motion of the blade carrier 14 in the direction of the arrows X. The carrier 14 is slidably mounted in the cage 12. Furthermore, the carrier can pivot to a small extent about axis 18 at a top part 20 of the cage 12, while a bottom part 22 of the cage 12 allows pivotal movement of the carrier 14 in the direction of the arrows Y. Biassing means (not shown) in the bottom part 22 press the carrier 14 towards the right in the drawings. The carrier 14 carries a removable blade 24 at its lower end. The blade 24 is supported in the direction of feed of the jigsaw (see arrow F in Figure 1) by a support wheel 26. The support wheel is journalled in a bell crank lever 28 pivoted in the housing about axis 30. The other end, 32 of the bell crank lever is acted on by a drive pin 34 slidably received in a cross bore 38 of an adjustment shaft 36. The adjustment shaft 36 is rotatably journalled in the housing about an axis 40. The other end of the drive pin 34 is acted upon by a fork lever 42 pivoted in the housing about an axis 44 (see also Figure 2). The fork lever 42 has fork arms 46a, b journalled around a circular cam surface 48 eccentrically formed on gear 8. The cam surface 8 also mounts a counter-weight 50 which is adapted to balance the forces generated by the reciprocation of the carrier 14 etc. Thus it is arranged to reciprocate with carrier 14 in the direction of the arrows x, but 180° out of phase with respect thereto. The fork lever 42 and bell crank lever 28 are each provided with circular cam surfaces 52, 54 respectively, each of which is acted upon by the drive pin 34 and each of which is centred on the rotation axis 40 of the adjustment shaft 36. It will be appreciated that while rotation of the shaft 36 has no effect on the mechanical advantage of the pin's action on the bell crank lever 28, it has a great effect on that of the fork lever 42. Thus in the position shown in Figure 2, the reciprocation of the fork lever 42 between the two positions shown (one in dashed, the other in solid lines) as the gear 8 rotates, causes the drive pin 34 to reciprocate along its axis by an amount W. This reciprocation is transmitted from surface 52, through the pin 34, to the surface 54 on the bell crank lever 28. Referring again to Figure 1, the bell crank lever passes this reciprocation to the blade Y and against the bias of the biassing means in the bottom part 22 of the cage 12. If, however, the shaft 36 is rotated about its axis 40 so that the drive pin 34 adopts the position shown in dotted lines in Figure 2, then it can be seen that the reciprocation of the fork lever 42 has no effect on the position of the pin 34 and consquently there is no reciprocation in the Y direction of the blade 24. Intermediate positions of the shaft 36 and pin 34 results in intermediate reciprocation of the blade. Rotational adjustment of the shaft 36 is effected by an adjustment pin. 60 which is a sliding fit in another cross-bore 61 of the shaft 36. This pin is pivoted at its other end in a carrier 62 which is slidably disposed at the side of the housing 2. A knob 64 is connected to the carrier 62 and is manually actuable. The switch 70 formed by carrier 62 and knob 64 is shown in greater detail in Figures 4 to 6. The carrier 62 is essentially rectangular and has two slots 68 through which legs 72 of the knob 64 are adapted to pass. The housing 2 has in this region a rectangular aperture 76 through which the legs 72 protrude. A shoulder 78 on the knob 64 prevents the knob from passing through aperture 76. The carrier 62 has a spring 80 mounted on it. The spring is mounted on two studs 82 and has slots corresponding with the slots 68. The legs 72 of the knob 64 are adapted to snap into engagement with the edges of the slots formed in the spring 80. A seal 84 around the aperture 76 seals the carrier 62 with respect to the housing, so preventing the ingression of dust. The carrier 62 has a lug 90, supported by fillets 92 and in the end of the lug 90 is formed a bore 94 in which the adjustment pin 60 is pivotolly located. It is held against axial movement in the bore 94 by its location in shaft 36. The spring 80 has a lip 81 which is adapted to snap into one of four detents 83 formed in the housing 2. These provide positive locations of the switch 70 between two extreme positions and two intermediate positions. It should be appreciated that reference herein to the "housing" of the jigsaw also includes other parts secured in the housing. In this respect, most of the components referred to herein as being mounted in or with respect to the housing are in fact mounted in other components which themselves are ultimately mounted in the housing. This is particularly the case with respect to the rotational and reciprocational elements described above which may be mounted in a separate housing securely fixed to the motor. However, this has no relevance to the workings of the present invention. Thus by this simple mechanism for rotational adjustment of the shaft 36, the need for it to project out of the rear of the housing 2 to be provided with a knob for manual adjustment is removed. This enables the gap between the bottom of the housing 2 and the shoe plate 11 of the saw to be employed as a passage 100 for a vacuum extraction means for removing dust as it is produced during sawing. Thus passage 100 opens at 102 above and behind the blade 24 and may be connected at 104 to a vacuum source such as a domestic vacuum cleaner or special vacuum extractor (neither shown). In any event, this design provides for a more balanced styling and more compact arrangement of the saw as a whole.

Claims: A saw (1) comprising a housing (2) for a motor (5) which drives a gear (8) having a blade carrier (14) mounted thereon for reciprocation in a first direction (X), a cam surface (48) formed on said gear on which a fork lever (42) is journalled, the fork lever being pivoted in the housing about a first axis (44) lying perpendicular to said first direction and acting on one end of a drive pin (34) slidably mounted in a shaft (36) rotatably mounted in the housing about a second axis (40) parallel to said first axis, the other end of said drive pin acting on one end (32) of a bell crank lever (28) pivoted in said housing about a third axis (30) perpendicular to said first direction and said first and second axes, the other end of said bell crank lever carrying a support wheel (26) disposed behind and supporting in the direction of feed (F) of the saw a blade (24) carried by said carrier, means biassing said blade against the support wheel, the fork lever, pin and bell crank being arranged such that on rotation of said gear, the support wheel imparts a reciprocating motion, in said direction of feed of the saw, on the saw blade, rotation of said shaft altering the mechan-ical advantage of the connection between said fork and bell crank levers, characterised in that said shaft (36) carries an adjustment pin (60) mounted in a manually actuable slide switch (70) mounted for movement in the housing in the plane of rotation of the shaft. A saw as claimed in Claim 1, characterised in that said switch is mounted in the housing for movement in said first direction along a straight line, distance means (61) being provided to allow for the change in distance of said switch from said shaft. A saw as claimed in Claim 2, characterised in that said distance means comprises said adjustment pin being pivoted (94) in said switch and being a sliding fit in a cross-bore (61) in said shaft. A saw as claimed in Claim 2 or 3, characterised in that said switch comprises a knob (64) slidably mounted in a rectangular slot (76) in said housing, a switch carrier (62) mounted on said knob inside the housing and covering said slot, and spring means (80) mounted on said switch carrier and being adapted to engage one of several detents (83) to locate said switch in different positions, the switch carrier having pivot means (94) to pivot said adjustment pin on the carrier. A saw as claimed in Claims 3 and 4, characterised in that said pivot means comprises a bore (94) in the switch carrier arranged parallel to said first and second axes. A saw as claimed in any preceding claim characterised in that it further comprises a vacuum extraction passage (100) formed in said housing below the motor and opening above and behind the blade.

Inventors: BATT DENNIS MALCOLM, BRIGGS ALAN WILLIAM, BATT, DENNIS MALCOLM, BRIGGS, ALAN WILLIAM
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1992
Main classification: B23D49
IPC codes: B23D49, B23D59, B27B19, B23D51