Portable circular saw with riving knife drive mechanism

Abstract: A portable circular saw (10) includes motor-and-gear case (20) pivotally supported on a guide shoe (12) by a rear pivot mechanism (26) for rotation about a transverse rear pivot axis, thus allowing for selective adjustment of the blade cutting depth on the opposite side of the shoe. In such an arrangement, the depth of cut setting is increased and decreased when the motor-and-gear case is rotated relative to the shoe in respective first and second directions, while an upper pivotal blade guard (30), which is mounted on the motor-and-gear case for rotation about the spindle (24), rotates in opposite rotational directions in response to respective increases and decreases in the depth of cut setting. Cam and cam follower mechanisms (35, 52, 53, 66, 84, 86) maintain the riving knife (62), the blade (19) and shoe (12) in the same relative angular orientation in a fore-and-aft cutting plane regardless of the depth of cut setting. Such riving knife actuation is accomplished by such mechanisms in response to the rotation of the rear-pivoted motor-and-gear case and the corresponding opposite rotation of the front-pivoted upper gear case.

Description: BACKGROUND AND SUMMARY OF THE INVENTION The invention relates to portable circular saws having riving knives positioned in a rearward aft location relative to the cutting blade and adapted to extend into the saw kerf. Such riving knives are configured to substantially prevent the severed portions of the cut workpiece from moving toward one another and pinching the blade, thus creating undesirable drag on the saw blade. More particularly, the present invention relates to a drive mechanism for a movable riving knife that maintains a constant angular orientation and radial clearance relative to the saw blade, and a constant depth projection relative to the saw blade, regardless of the adjusted depth of cut of the saw blade. The distance between the lower, free end of the riving knife and a lower tangent of the cutting blade parallel to the guide shoe is maintained, regardless of the depth of cut setting. Such a portable saw is disclosed in CH-A-276 861. The present invention is adapted for applications in portable circular saws having rear-pivoting motor-and-gear cases. Riving knives, which are also sometimes called "splitters", have been provided in a variety of sawing or cutting apparatuses in order to keep the kerf open between severed portions of a workpiece, thereby substantially preventing the kerf from closing and allowing the workpiece portions to pinch the cutting blade. Such riving knife applications have included stationary and portable circular saws. In the portable circular saw applications, precise control of the riving knife position has frequently presented a problem in that the angular orientation and fore-and-aft location have been difficult to control in response to depth-of-cut adjustments of the saw blade relative to the guide shoe. In order to overcome these problems, various mechanisms, including four-bar linkages, sometimes called "parallelogram linkage arrangements", have been provided in order to impart the desired relative motion to the riving knife to maintain the orientation of the riving knife relatively constant during depth-of-cut adjustment. Such four-bar linkage arrangements for riving knife drive mechanisms in portable circular saws have suffered the disadvantage of being non-linear in terms of their response to depth-of-cut adjustments, thus making precise control of the riving knife position and orientation difficult. They have also been found to introduce unacceptable "play" into the riving knife motion, due to the tolerances required for relative motion of the various linkage members in such four-bar linkage arrangements. Such previous mechanisms also frequently involve an inordinately large number of parts, thus complicating the manufacture, assembly, and operation of the mechanisms, as well as not being sturdy enough to withstand the rough treatment to which such portable circular saws are frequently subjected in construction operations. Therefore, an object of the present invention is to provide an improved riving knife drive mechanism overcoming the problem associated with the prior art mechanisms. CH-A-276 786 discloses a device according to the preamble of claim 1. The problems are overcome by the characterising features of claim 1. Preferably, the cam and follower means includes three cam surface and cam follower mechanisms. The first mechanism is interconnected between the shoe and the guard for rotating the guard about the spindle in response to depth of cut setting adjustments. The second mechanism is interconnected between the riving knife and the drive link. The third mechanism is interconnected between the gear case and the drive link. The second and third mechanisms maintain the riving knife in the same orientation relative to the shoe regardless of the depth of cut setting. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a right side view of an exemplary portable circular saw according to the present invention, with the saw set for a maximum cutting depth. Figure 2 is a view similar to that of Figure 1, with the saw also adjusted for a maximum depth of cut, but with the lower blade guard and the outer half of the upper blade guard removed for clarity in order to illustrate various internal components. Figure 3 is a view similar to that of Figure 2, but with the saw adjusted for a shallower depth of cut. Figure 4 is a view similar to that of Figures 2 and 3, nut with the portable circular saw adjusted for a minimum depth of cut, wherein the blade would barely project from the guide shoe. Figure 5 is a partial exploded view of the exemplary portable circular saw of Figures 1 through 4, with the riving knife, riving knife carrier, and drive link components disassembled for purposes of illustration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of illustration of one preferred embodiment of the invention, Figures 1 through 5 depict an exemplary portable circular saw 10, equipped with a riving knife drive arrangement according to the present invention. The portable circular saw 10 generally includes a guide shoe 12 extending from the front or fore end 14 of the saw to the rear or aft end 16 of the saw 10. The guide shoe 12 includes an opening 13 (see Figure 5), through which a cutting blade 18 extends. The cutting blade 18 is supported on a spindle 25 for rotation in a fore-and-aft-extending cutting plane 19 about a spindle assembly 24 on a motor-and-gear case 20. The motor-and-gear case 20 generally includes a handle 21, a power supply 22, and a pivot arm member 23, pivotally attached to the guide shoe 12 by way of a rear pivot 26. Such pivotal attachment accommodates selective cutting depth adjustment, an example of which is described in more detail in United States Patent No. 4,982,501, issued January 8, 1991, to William D. Sauerwein, et al. An upper guard 30 is mounted for rotation on the spindle assembly 24, as well as being pivotally interconnected with the shoe 12 by way of a front pivot assembly 80. The front pivot assembly 80, perhaps best shown in Figures 3 and 4, includes a front pivot link 82, with an elongated slot 84 forming a camming surface therein. A pin or cam 86, which is fixedly attached to the upper guard 30, is slidably received within the slot or camming surface 84 formed in the front link 82. By way of the clamping assembly 40, which includes a clamping knob 42, the cutting depth of the blade 18 can be set and maintained by loosening the clamping knob 42, to facilitate pivoting the motor-and-gear case 20 about the rear pivot mechanism 26 in first or second clockwise directions in order to respectively increase or decrease the depth of cut setting. In response to this pivotal adjustment, the upper guard 30 rotates in the opposite direction about the spindle assembly 24, that is, in first or second rotational directions in response to decreasing or increasing the depth of cut setting, respectively. In Figures 2 through 5, the lower guard 32 and the outer half 34 of the upper guard 30 have been removed, leaving only the inner half 33 of the upper guard 30, in order to illustrate other internal components of the riving knife drive mechanism. The riving knife drive mechanism includes a drive link 50, pivotally attached by way of a pivot pin 51 to the upper guard 30 and having a slot or camming surface 52 formed therein, which slidably receives a cam follower or pin 35 on the pivot arm member 23 of the motor-and-gear case 20. The drive link 50 also includes a cam follower or pin 53 fixedly attached thereto, the purpose of which will be explained below. A riving knife assembly 60 includes a riving knife 62 connected by way of an adjusting mechanism 63 to a riving knife carrier 64, which is in turn disposed for rotational pivotal motion about the spindle assembly 24. The adjusting mechanism 63 is adapted to releasably hold the riving knife 62 in a fixed position and orientation with respect to the riving knife carrier 64, but provides for a relatively small amount of adjustment therebetween in order to accommodate cutting blades of slightly different sizes or cutting blades whose outer diameters have changed slightly due to repeated sharpenings. Ordinarily, however, the adjusting mechanism 63 fixedly retains the riving knife 62 in a fixed position and orientation relative to the riving knife carrier 64. The riving knife 62 also includes a free end 67, which is disposed below the guide shoe 12, and the riving knife carrier 64 includes a slot or camming surface 66 formed therein, in which the above-mentioned cam follower or pin 53 on the drive link 50 is slidably received. By way of the slidable engagements of the above-described camming surfaces and their respective cam followers or pins, the riving knife 62 is moved in response to depth-of-cut adjustments in order to maintain the riving knife 62 in a substantially constant orientation relative to the blade 18 and the guide shoe 12 in a fore-and-aft plane, regardless of the selected depth-of-cut setting. Such driving actuation of the riving knife 62 is accomplished in response to the pivotal motion of the motor-and-gear case 20 about the rear pivot 26 and the corresponding opposite pivotal motion of the upper guard assembly 30 about the sliding front pivot assembly 80. When the depth of cut is selectively adjusted, the upper guard assembly 30 pivots about the spindle assembly 24, and the pin or cam follower 86 on the upper guard assembly 30 slides and pivots within the elongated slot or camming surface 84 of the front link 82 in order to accommodate the pivotal movement of the motor-and-gear case 20 about the rear pivot 26. When the upper guard assembly 30 rotates, the drive link 50 pivots about the pivot pin 51 fixedly mounted on the upper guard assembly 30. At the same time, the generally arcuate slot or camming surface 52 of the drive link 50 slidably engages the camming surface or pin 35 fixedly mounted on the pivot arm member 23 of the motor-and-gear case 20. This causes movement of the cam follower or pin 53 on the drive link 50 within the slot or camming surface 66 of the riving knife carrier 64. The combination of these motions, which are imparted to the riving knife carrier 64 by the cam follower or pin 53, causes the riving knife carrier 64 and the riving knife 62 to move along a predetermined locus toward and away from the guide shoe 12, thus maintaining the desired orientation of the riving knife 62 with respect to the blade 18 and the guide shoe 12. The angular orientation 70 of the riving knife 62 relative to the guide shoe 12 and the distance between the free end 67 of the riving knife 62 and the lower tangent 72 on the adjusted blade 18 is maintained, with such tangent 72 being substantially parallel to the guide shoe 12. As will be appreciated, a number of advantages flow from the practice of the present invention. First, the riving knife drive mechanism of the present invention provides a relatively linear, precise control of the riving knife position and orientation in response to adjustment of the depth of cut. Secondly, the mechanism is sturdier and more rigid than traditional four-bar linkage arrangements. Thirdly, the mechanism is relatively simple and has a relatively low number of parts, thereby facilitating operation of the mechanism and the ease and economy of manufacture and assembly. Additional advantages of the present invention will be apparent to those skilled in the art from the foregoing description and appended claims. The foregoing discussion discloses and describes merely exemplary embodiments of the present invention for purposes of illustration only.

Claims: A portable circular saw (10) comprising : a guide shoe (12) having a forward end (14) and a rearward end (16); a motor-and-gear case (20) disposed on one side of the shoe and having a transverse output spindle (24) for supporting a blade (19) in a fore-and-aft cutting plane; a riving knife (62) interconnected for pivotal rotation about the spindle; cam-and-follower means (35, 52, 53, 66, 84, 86) interconnecting the shoe, the guard, the case, and the riving knife for rotating the guard in first and second rotational directions when the depth of cut setting is decreased and increased, respectively, and for maintaining the riving knife and the shoe in the same relative angular orientation in fore-and-aft cutting plane regardless of the depth of cut setting; and an upper blade guard (30) pivotably mounted on the motor-and-gear case for rotation about the spindle; characterised by : a rear pivot (26) for pivotally supporting the motor-and-gear case on the shoe for rotation about a transverse rear pivot axis and for adjusting the extension of the blade on the opposite side of the shoe in order to thereby adjust the depth of cut setting of the blade, the depth of cut setting being increased and decreased when the motor-and-gear case is rotated relative to the shoe in the first and second rotational directions, respectively, and a drive link (50) pivotally connected to the guard at a location between the spindle and rear pivot. A portable circular saw according to claim 1, wherein the cam-and-follower means comprises: a first cam surface and cam follower mechanism (84, 86) interconnected between the shoe (12) and the guard (30) for rotating the guard about the spindle in the first and second rotational directions when the depth of cut setting is decreased and increased, respectively; a second cam surface and cam follower mechanism (66, 53) interconnected between the riving knife (62) and the drive link (50); a third mechanism (52, 35) interconnected between the gear case and the drive link; and the second and third mechanisms maintaining the riving knife in the same orientation relative to the shoe regardless of the depth of cut setting. A portable circular saw according to claim 2, wherein the first mechanism includes (a) a first cam surface (84) that interconnects with the shoe and extends generally in the fore-and-aft direction, and (b) a first cam follower (86) that extends transversely from the guard. A portable circular saw according to claim 2, wherein the second mechanism includes (a) a second cam surface (66) that is interconnected with the riving knife and extends generally in the fore-and-aft direction, and (b) a second cam follower (53) that is fixed to and extends transversely from the drive link. A portable circular saw according to claim 2, wherein the third mechanism includes (a) a third cam surface (52) that is formed in the drive link and extends generally in the fore-and-aft direction, and (b) a third cam follower (35) that is fixed to and extends transversely from the case. A portable circular saw according to claims 2-4 or 5, wherein the first mechanism (84, 86) is located forward of the spindle, the pivotal connection (51) between the drive link and the guard being located rearwardly of the spindle, the second mechanism (66, 53) is located rearwardly of the pivotal connection between the drive link and the guard, the third mechanism is located rearwardly of the second cam surface and cam follower mechanism, and the rear pivot (26) is located rearwardly of the third cam surface and cam follower mechanism. A portable circular saw according to claims 1 or 6, characterized by a riving knife carrier (64), pivotally mounted at a first end about the spindle and having the riving knife fixed thereto at a second opposite end. A portable circular saw of claims 1 or 6, wherein said cam-and-follower means maintains a constant distance regardless of the depth of cut setting between a free end (67) of said riving knife on a distal side of the shoe opposite the motor-and-gear case and a tangent (72) to the blade on said distal side of the shoe, said tangent being generally parallel to the shoe.

Inventors: SAUERWEIN WILLIAM D, STUMPF WILLIAM R, SAUERWEIN, WILLIAM D., STUMPF, WILLIAM R.
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1993
Main classification: B27G19
IPC codes: B27G19