GB2273078A - Adjustable riving knife - Google Patents

Abstract

The rotary saw (2, Fig. 1 not shown) comprises a rotary saw blade (5), a housing (6) partially enclosing the saw blade and a riving knife (7) movably attached to the saw housing; the riving knife is clamped at fixed positions relative to the housing via a sliding member (13) in a slot (14) in the perimeter of the housing. The riving knife can be retracted entirely to a position behind the housing, thereby enabling the rotary saw to be reconfigured as a mitre saw (30), and can be moved from a first position above a tangent of the blade, which tangent is parallel the table and to a second position, the knife being below the tangent. <IMAGE>

Description

ADJUSTABLE RIVING KNIFE The present invention relates to a rotary saw having an adjustable riving knife associated therewith.

Motor driven rotary saws are well known in the machine tool art and are commonly configured as bench saws. In this configuration the rotary saw machinery is positioned below a work surface or table with an edge of the rotary saw blade projecting upwardly through a slot in the table. Work pieces are cut by sliding them along the work surface into the blade. An essential feature of such a bench saw is the presence of a riving knife situated behind the blade of the saw. The riving knife is a thin fixed blade that is upstanding from the work surface and coplanar with the saw blade. As workpieces pass around the saw blade after having been cut by its leading edge the riving knife ensures that the cut workpiece does not close on the blade, risking jamming of the blade and potentially throwing the workpiece up into the face of the operator.

There are two modes of operation for a riving knife.

In the more usual mode of operation the saw is being used to cut workpieces that are thinner than the height by which the saw blade projects above the work surface, with the result that the workpieces are sawn in two. In this event it is usual for the riving knife to have its top edge projecting above the top of the circular saw blade.

A protective cover may then be attached to or pivoted to the top of the riving knife. Alternatively, a second blade may be positioned behind the riving knife carrying a guard which is adapted to cover the top of the riving knife and under which workpieces are passed during cutting.

In an alternative mode of operation the bench saw is used to cut workpieces that are thicker than the height by which the saw blade projects above the work surface, with the result that the saw merely cuts a groove in the workpiece. In this case the top of the riving knife must be level with, or below the level of, the top of the saw blade in order to avoid blocking the workpiece being pushed through the blade.

The above-described alternative configurations give rise to a need for a riving knife that can be moved up and down while remaining adjacent to, and coplanar with, the saw blade. Regulations dictate that riving knives should only be detachable by the user through use of a special tool. Consequently this need is not easily met.

Furthermore, it may be desirable to retract the riving knife entirely under some circumstances. For example, some multifunctional work benches allow the same rotary saw to be configured either as a bench saw, as described above, or as a mitre saw, in which case the rotary saw is pivoted above the work surface such that the pivoting action plunges the rotary saw blade down through the slot in the work surface. There is no need for a riving knife when the rotary saw is configured as a mitre saw.

Accordingly, it is an object of the present invention to provide a riving knife for a rotary bench saw that can quickly and easily be moved up and down relative to the rotary saw blade while remaining proximate to and coplanar with the rotary saw blade. It is a further object of the present invention to provide a riving knife having the above characteristics that can speedily be retracted when it is desired to reconfigure the rotary saw as a mitre saw.

The present invention provides a rotary saw comprising a rotary saw blade, a table through which the blade projects, a housing partially enclosing the blade, a riving knife connected to the housing and releaseable clamping means to clamp the riving knife at a fixed position relative to the housing, the riving knife being adjustable between two positions relative to the blade without disconnection from the housing, in a first position a point of the knife being above a tangent of the blade, which tangent is parallel said table, and having means for attachment of a guard thereto and in a second position the knife being below said tangent.

The riving knife is preferably movable along an arcuate path substantially coplanar with the plane of the rotary saw blade. Preferably the arcuate path is a substantially circular path substantially concentric with the rotary saw blade. By following such an arcuate or circular path the blade of the riving knife is kept proximate to the edge of the rotary saw blade as the riving knife is moved up or down.

The riving knife may be movably attached to the housing, for example, by pivoting the riving knife from a pivot member provided near the centre of the housing.

However, in preferred embodiments the riving knife is movably attached to the housing by means of a sliding member, said sliding member being joined to the riving knife and slidably inserted in a slot in the housing.

The slot will normally extend some distance around part of the perimeter of the housing such that sliding the slidable member in the slot causes the riving knife to move along an arcuate path corresponding to that part of the perimeter of the housing.

The releasable clamping means used to clamp the riving knife will normally be a screw or bolt fitting of some kind. For example, in the preferred embodiment described above the releasable clamping means preferably comprises a screw or a bolt fitting, whereby tightening the screw or the bolt fitting clamps the housing between the sliding member and the riving knife. That is to say, tightening the screw presses together the sliding member and the riving knife so that the edges of the slit in the housing are gripped between the slidable member and the riving knife thereby clamping the riving knife at a fixed position relative to the housing.The screw or bolt fitting may for example comprise a terminal knob, lever or wing nut so that the fitting can be tightened or released by hand, in which event a circlip or the like prevents complete disconnection of the lever or wingnut thereby preventing removal of the riving knife without use of a special tool.

The riving knife preferably comprises a riving blade clamped to a carrier member. Preferably the means used to clamp the riving blade to the carrier member permits some adjustment of the relative position of the riving blade and the carrier member. This fine adjustment of the position of the riving blade is in addition to the gross adjustment provided by the movement of the riving knife as a whole relative to the housing, as described above.

In preferred embodiments the riving blade is clamped to the carrier member by means of a screw or a bolt extending through a slot in the riving blade, whereby the relative positions of the riving blade and the carrier may be adjusted. The adjustment may be by sliding the screw or bolt along the slot in the riving blade. Once the relative position of the riving blade and the carrier member has been adjusted the riving blade is then secured in the desired position by tightening the screw or bolt.

The blade may also be removed entirely by loosening and withdrawing the screw or bolt.

Preferably the rotary saw also comprises means to adjust the alignment of the riving knife with the rotary saw blade. The alignment of the riving knife and the rotary saw blade should be such that the riving knife and the rotary saw blade lie in the same plane in order to ensure a smooth cutting and riving operation. The means to adjust the alignment may conveniently comprise set screws engaged in threaded bores in the carrier member and abutting either the housing or the riving blade.

The rotary saw according to the present invention may be configured as a bench saw, in which case the rotary saw is positioned with the housing situated below the table or work surface and with the exposed part of the saw blade and the riving blade projecting upwardly through a slot in the table. The riving knife is movably attached to the housing below the table leaving the table unencumbered by anything other than the saw blade and the riving blade. The height of the top of the riving blade above the table can be adjusted by the operator quickly and safely from below the table. Moreover, because the riving knife is attached to the housing of the rotary saw, adjustment of the height of the riving knife does not cause the riving knife to come out of alignment with the rotary saw blade.Finally, when the bench sawing operation is completed both the rotary saw blade and the riving knife can be retracted below the work surface in a single operation so as to leave the work surface entirely unencumbered for further machining operations.

According to preferred embodiments of the present invention the rotary saw can be used both in a bench saw configuration as described above and also as a mitre saw.

In the latter case the rotary saw is positioned above the other side of the inverted table and pivoted so that the rotary saw blade can be plunged through the slot in the table to cut workpieces positioned over the slot. In this configuration there is no need for a riving knife, and in fact it is preferable to remove the riving knife from the vicinity of the rotary saw blade. Therefore, preferably, the riving knife can be retracted to a position where it is substantially separated from the rotary saw blade and can be rotated about an axis substantially perpendicular to the axis of rotation of the rotary saw blade, such as about the screw joining the riving knife to the slidable member engaged in the housing, so as to lie beside and outside the housing.

An embodiment of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 shows in side elevation a rotary saw according to the present invention configured as a bench saw; FIGURE 2 shows a cross-sectional view of the riving knife arrangement in the rotary saw of Figure 1; FIGURE 3 shows a front elevation of the riving knife in the rotary saw of Figure 1; FIGURE 4 shows a cross-section through part of the riving knife arrangement shown in Figure 2, the crosssection being taken along line A-A of Figure 2 and perpendicular to the plane of the rotary saw blade; and FIGURE 5 shows in side elevation the rotary saw reconfigured as a mitre saw with the riving knife retracted.

Referring to Figure 1, the rotary saw 1 is normally configured as a bench saw 2. The bench saw 2 comprises a bench 3 supported on a stand (not shown). The rotary saw 1 is positioned inside the bench 3 beneath a work surface or table 4. The rotary saw blade 5 projects upwardly through a slot 25 (see Figure 3) in the work surface.

The portion of the rotary saw blade below the work surface is enclosed in a housing 6. A riving knife 7 is movably attached to the housing 6. The riving knife comprises a riving blade 8 that projects through the same slot in the work surface as the rotary saw blade and that is positioned immediately behind the rotary saw blade.

The Figure shows the top of the riving knife projecting above the level of the tangent of the rotary saw blade, which is parallel the table 4. This is the normal configuration when the saw is being used to cut workpieces that are thinner than the height of the rotary saw blade above the surface. A cover 9 is detachably pivoted to the top of the riving knife about axis 10.

Workpieces lift the front of the cover 9 before they contact the rotary saw blade 5.

Referring to Figure 2, the riving knife 7 comprises the riving blade 8 joined to a carrier member 11. A stud 12 joins the carrier member 11 to a sliding member 13, which is engaged in a slot 14 in the perimeter of the housing 6. The sliding member is slidable in the slot along a substantially circular path concentric with the rotary saw blade. The circular path followed by the riving knife as the sliding member is moved permits the riving blade to remain close to the edge of the rotary saw blade as the riving knife is raised and lowered.

The riving knife is shown in the lowered position in broken lines on Figure 2. It can be seen that in this position the top of the riving knife is below the level of the top of the rotary saw blade and the cover 9 has been removed, thereby allowing the bench saw to be used for groove cutting in workpieces thicker than the height of the rotary saw blade above the work surface.

The clamping means used to clamp the riving knife at a fixed position during cutting operations is shown in more detail in Figure 4. The slot 14 in the housing 6 has inwardly projecting lips 15. The sliding member 13 is positioned in the slot and has complementary lips 16 for abutting the lips 15 of the slot. The carrier member 11 of the riving knife 7 is located outside the slot and overlaps the lips 15 of the slot. The cylindrical stud 12 is attached at one end to the sliding member 13 and extends upwardly through a bore 17 near the centre of the carrier member 11. The upper part 18 of the stud 12 projects beyond top of the carrier 11 and is provided with a bolt thread. A knob 19 having a complementary threaded bore is fitted to the stud 12 and is retained on the stud 12 against removal without the use of a separate tool by means of a circlip 20. The carrier member 11 is provided with set screws 21 for abutting the lips 15 of the slot 14.

In operation, tightening the knob 19 causes the lips 15 of the slot 14 to be gripped between the sliding member 13 and the set screws 21 of the carrier member 11, thereby clamping the riving knife to the lips 15 of the slot 14 and preventing further movement of the riving knife relative to the housing. The alignment of the riving knife with the rotary saw blade can be adjusted by means of the set screws 21, before tightening knob 19.

Referring to Figures 3 and 4, the riving blade 8 is joined to the carrier member 11 by means of a bolt 22 mounted on a head 26 and passing through substantially rectangular eye 23 in the riving blade 8. When the bolt is loosened the riving knife can be raised and lowered for vertical adjustments of the riving blade in the carrier member 11. The carrier member 11 has pegs 27 which pass through the eye 23 and engage corresponding dents 28 in the head 26. The pegs maintain alignment of the blade 8 with respect to the carrier 11 and also prevent rotation of the head 26 when the bolt 22 is tightened. When the bolt 22 is tightened the riving blade 8 is gripped securely in the carrier 11 at the selected position.

Referring to Figure 5, the rotary saw 1 can be reconfigured as a mitre saw 301rotating the table 4 and pivoting the saw 1 above the other side of the work surface 4 from a pivot 24. The pivoting operation then plunges the rotary saw blade through the slot in the work surface. In order to reconfigure the saw as a mitre saw the riving knife 7 has been retracted to a position where it is separated from the rotary saw blade 5.

Referring to Figures 2, 3 and 4, the riving knife 7 is retracted as follows. First, the knob 19 is unscrewed sufficiently to allow the carrier member 11 to be lifted clear of the lips 15 of the slot 14. Then the carrier member and attached riving blade are rotated about the stud 12 by approximately 180 degrees until the riving blade abuts the housing 6. A recess is provided in the housing to receive the riving blade, with means to retain the riving blade in abutment with the housing. The riving knife is secured in the retracted position by screwing down the knob 19 once the retraction operation is complete, thereby clamping the riving knife in the retracted position.

The embodiment of the present invention described above is intended by way of example only. Alternative embodiments falling within the scope of the present invention will no doubt be apparent to the skilled reader.

Claims (10)

1. A rotary saw comprising a rotary saw blade, a table through which the blade projects, a housing partially enclosing the blade, a riving knife connected to the housing and releasable clamping means to clamp the riving knife at a fixed position relative to the housing, the riving knife being adjustable between two positions relative to the blade without disconnection from the housing, in a first position a point of the knife being above a tangent of the blade, which tangent is parallel said table, and having means for attachment of a guard thereto and in a second position the knife being below said tangent.

2. A rotary saw according to claim 1 wherein the riving knife is movable along an arcuate path substantially coplanar with the plane of the rotary saw blade.

3. A rotary saw according to claim 2 wherein the riving knife is movable along a substantially circular path substantially concentric with the rotary saw blade.

4. A rotary saw according to any preceding claim wherein the riving knife is movably attached to the housing by means of a sliding member, said sliding member being joined to the riving knife and slidably inserted in a slot in the housing.

5. A rotary saw according to claim 4 wherein the sliding member is joined to the riving knife by means of a screw or a bolt fitting, whereby tightening the screw or the bolt fitting clamps the housing between the sliding member and the riving knife.

6. A rotary saw according to any preceding claim wherein the riving knife comprises a riving blade clamped to a carrier member.

7. A rotary saw according to claim 6 wherein the riving blade is clamped to the carrier member by means of a screw or bolt extending through a slot in the riving blade, whereby the relative positions of the riving blade and the carrier member may be adjusted.

8. A rotary saw according to any preceding claim further comprising means to adjust the alignment of the riving knife with the rotary saw blade.

9. A rotary saw according to any preceding claim wherein the riving knife can be retracted to a position where it is substantially separated from the rotary saw blade and can be rotated about an axis substantially perpendicular to the axis of the rotation of the rotary saw blade so as to lie beside and outside the housing.

10. A rotary saw substantially as hereinbefore described with reference to the accompanying drawings.