GB2307443A

GB2307443A - Riving knife

Info

Publication number: GB2307443A
Application number: GB9524550A
Authority: GB
Inventors: David Arthur Copper
Original assignee: Draper Tools Ltd
Current assignee: Draper Tools Ltd
Priority date: 1995-11-24
Filing date: 1995-11-24
Publication date: 1997-05-28
Anticipated expiration: 2015-11-24
Also published as: CN1075425C; HK1013274A1; GB9524550D0; TW350811B; CN1159971A; GB2307443B

Abstract

A riving knife (1) is mounted externally of a circular saw machine such that a curved leading edge of a blade (5) of the riving knife is close to and generally conforms to the arc described by the rim of the saw blade. The blade (1) has a gantry part (8) extending from a mounting part (3) and arranged to be disposed above the level of a saw table (2) when the knife is mounted, a blade part (5) depends from said gantry part towards said table in the shape of a tapering finger. The position of the blade part (5) in the plane of rotation of the saw blade and with respect to said table can be manually adjusted to permit a curved leading edge of the blade part to be disposed proximate the arc described by the rim of the saw blade.

Description

RIVING KNIFE The invention relates to a riving knife or splitter for a table-mounted saw and, in particular, to an adjustable riving knife for a table-mounted circular saw.

It is known to use a riving knife with table-mounted circular saws so as to prevent the cut wood closing on the blade. The riving knife generally has a blade with a leading edge conforming to the rim of a circular saw blade. The riving knife blade is positioned behind the saw blade with respect to the direction of the advancing workpiece and is generally radial with the rim of the saw blade when the blade is in a fixed position.

Figure 1 shows a prior art riving knife 1 which is mounted externally of the saw machine by means of a bracket, not shown, located below the level of a work bench or table 2. The knife 1 has a mounting part 3 which has a slot 4 for receiving bolts so as to bolt the knife to said bracket. The mounting part 3 extends above the surface of the table 2. A blade part 5 contiguous with said mounting part 3 has a leading edge shaped to follow the rim of a circular saw blade. A blade guard may be fixed to the knife 1 by means of a blade guard fixing hole 6. Furthermore, anti-kickback fingers may be attached either side of the knife 1 by means of a fixing point 7. The anti-kickback fingers are spring loaded so as to be urged to press down on the workpiece.A hole 10 in the riving knife receives a retaining pin (not shown) which prevents rotation of the anti-kickback fingers past a predetermined point.

It is noted that the riving knife shown in Figure 1 extends above the arc described by the rim of the circular saw blade. Such a riving knife cannot, therefore, be used to form cuts which are less than the full depth of the work piece Table-mounted circular saw apparatus generally comprise a table supported on a frame or saw body. The body houses the saw apparatus supported below the level of the table and including a motor assembly and an arbor mechanism which is arranged for up and down movement of the circular saw blade. It is also common for the arbor mechanism to allow tilting of the saw blade to different cutting planes. Thus, slot 4 is arranged to allow a small amount of movement in the cutting plane so that the riving knife is not obstructed by the table as the mechanism tilts.However, it is important that in all positions of the saw blade the riving knife blade extends down to the table surface so that there is no possibility of the workpiece closing behind the saw blade.

The circular saw blade extends from below the table through a saw blade aperture in the table and the depth of cut is adjusted by raising and lowering the saw blade relative to the surface of the table by means of the arbor mechanism. The depth of cut may also be altered by substituting different radius saw blades though most tables are generally used with a given radius of saw blade for optimum working, for example a 10 inch blade.

With the development of European Standards in this field it is now desired to maintain the distance between the rim of the circular saw blade and the leading edge of the riving knife blade within predetermined limits. It can be seen that, with the riving knife of figure 1, the distance between the knife blade and the saw blade varies as the depth of cut is increased or decreased. Moreover, it is clear that, as the depth of cut is varied, a constant distance between the blade edge and the saw rim cannot be maintained by the riving knife shown in Fig. 1.

Furthermore, any movement of the riving knife in the plane of the saw blade away from the table will leave a gap (y) between the table and the bottom of the riving knife blade which will be deleterious to the splitting operation of the riving knife.

It is already known to provide a riving knife on the arbor mechanism within the body of a table-mounted circular saw which is mounted at its base and extends upwards through an extended part of the saw aperture.

Such knives rise and fall with the saw blade and maintain a constant radial distance between the saw rim and the knife blade. Even if the edge of the blade of such a knife does not conform with the rim of the saw blade, the maximum distance therebetween is still maintained. The position of the blade for internally mounted riving knives is slightly different than for externally mounted riving knives as the blade can be sized so as not to protrude above the arc described by the rim of the circular saw blade. It is thus possible with circular saw apparatus including an internally mounted riving knife to make cuts in a work piece with a depth less than the depth of the workpiece.

With both internally mounted and externally mounted riving knives, the leading edge of the knife blade is ideally positioned close to the rim of the saw blade and ideally in the form of an arc of a circle concentric with the rim of the saw blade. The new European Standard requires that above the saw table the radial distance between the riving knife and the toothed rim of the saw blade shall not at any point exceed 5mm at the depth of the cut set.

It has, therefore, been proposed to replace the riving knife according to Figure 1 mounted externally of the machine body, with an automatically adjustable riving knife within the body of the circular saw and mounted so as to rise and fall with the saw blade as described immediately above. To replace an externally mounted riving knife with an internally mounted, automatically adjusted, riving knife, it is necessary to extend the saw aperture of the machine to accommodate the blade of the automatically adjustable riving knife. Furthermore, additional parts are required to mount the riving knife.

Such knives will be referred to hereinafter as internal riving knives; this term includes all knives mounted within the body or frame of a table-mounted circular saw.

Other knives such as those mounted on the table or machine body, will be referred to as external riving knives, for example as shown in Figure 1. In this specification, a reference to a saw blade or circular saw includes a reference to a blade or saw with or without teeth, such as an abrasive cutting disc.

It is an object of the invention to provide a riving knife for a table-mounted saw which can be adjusted so as to maintain a maximum distance between the leading edge of the knife blade and a rim of a circular saw blade and which can be fitted to an existing circular saw design easily and cheaply.

Accordingly, the invention provides a table saw riving knife adapted to be mounted externally of a tablemounted saw body in the plane of rotation of a tablemounted saw blade, the knife comprising a mounting part, a gantry part extending from said mounting part and arranged to be disposed above the surface of a saw table when the knife is mounted, a blade part depending from said gantry part towards said table, the riving knife being arranged so that the position of the blade part in the plane of rotation of the saw blade and with respect to said table can be manually adjusted to permit a curved leading edge of the blade part to be disposed proximate the arc described by the rim of the saw blade over the operative cutting height range of the saw blade.

The knife of the present invention can be mounted on table-mounted saws as a replacement for a fixed position externally mounted riving knives without substantially redesigning the table or saw body. The knife of the present invention allows manual adjustment of the height of the knife blade so as to maintain a fixed or maximum distance between the leading edge of the blade and the rim of a circular saw, that is, the distance between the saw rim and the knife blade at any radial point on the saw rim, can be maintained within a fixed range.

The blade part may depend from said gantry part in the form of a finger tapering towards the table. An aperture exists, therefore, between the knife blade and the mounting part into which may be received a portion of the table so that a part of the knife blade can extend below the surface of the table through the saw blade aperture. The blade of the riving knife may be arranged to extend below the level of the table, or at least to the level of the table at all positions of the riving knife. This has the advantage that over the entire working range of the saw machine, the blade of the riving knife substantially conforms to the rim of the saw blade and provides a splitting operation over the entire depth of cut. Preferably, the radial distance between the saw rim and the knife blade can be adjusted to be under 5 mm at the depth of cut set.

In an embodiment, the mounting part has an elongate slot in a portion of the knife which is adapted to receive two bolts, the knife being secured to a bracket by any suitable locking means, for example, nuts. The use of two bolts prevents rotation of the knife.

The invention also provides table-mounted saw apparatus comprising the riving knife of the invention.

The invention also provides table-mounted saw apparatus comprising a table having a saw blade aperture, a body supporting the table, a motor assembly for driving a blade mounted thereon and supported below the surface of the table, means for mounting a riving knife externally of said body, a riving knife having a blade part and means cooperating with said mounting means, and adjustment means whereby the position of the blade part in the plane of rotation of the saw blade can be manually adjusted to permit the blade part to be disposed with a curved leading edge thereof proximate the arc described by the rim of the saw blade over the operative height range of the saw blade.

The riving knife may have a mounting part comprising said mounting means, and a gantry part extending from said mounting part and disposed above the level of the table. The blade part depends from said gantry part in the shape of a finger tapering towards said table.

The mounting means and said means cooperating therewith may comprise said adjustment means.

The means cooperating with said mounting means may comprise an elongate slot in said mounting part.

An embodiment of the invention will now be described by way of example only and with reference to the drawings, in which: Figure 1 is a side view of a prior art riving knife mounted to a circular saw table; and Figure 2 is side view of a riving knife according to the present invention.

Referring to Figure 1, this shows a prior art externally mounted riving knife 1 having a blade 5. The riving knife 1 is mounted onto a bracket (not shown) which is supported by a rod which extends into the body of the saw machine where it is fixed to a bracket supporting the saw motor assembly. The knife is mounted by means of two bolts which pass through slot 4 in a mounting part 3. The bracket is conveniently located below the level of the table so as not to impede the passage of a workpiece. The use of two bolts prevents rotation of the knife in the plane of rotation of the saw blade.

With this design, manual means (not shown) are provided on the front of the machine for tilting the saw blade 9 (shown in Figure 2), which is achieved by turning the motor about an axis such that the saw blade 9 and riving knife move about the same axis and are therefore in fixed alignment in a known manner. The slot 4 allows a small amount of movement of the riving knife so that the riving knife can tilt without contacting the table surface. However, in general, such knives are known as fixed riving knives.

It can be seen from Figure 1 that, if the saw blade is raised with respect to the table 2 (ie. the depth of cut is increased), the rim of the saw blade will approach the riving knife blade 5. Conversely, if the depth of cut is reduced, the distance between the saw blade and knife blade 5 increases. It is, therefore, not possible with this design to adjust the position of the riving knife so as to maintain, over the entire operating range of the saw blade, the radial distance between the saw blade and the knife blade within a predetermined range.

A riving knife according to the invention is shown in Figure 2. In Figure 2, like parts are given the same reference numerals as in Figure 1.

The riving knife of Figure 2 can be substituted for the riving knife according to Figure 1 and requires no modification of the saw table. The same bracket may be used to mount the knife on the machine by bolting it to the rod attached to the motor bracket. However, instead of the slot 4 (Figure 1), the embodiment of the invention shown in Figure 2 is provided with an elongate slot 4a in the mounting part 3 which allows the height to which the knife projects above the table surface to be adjusted.

The knife 1 extends above the level of the table in the manner described with regard to Figure 1 and the upper extremity is provided, in this embodiment, with an anti-kickback fingers fixing hole 7 and a blade guard fixing hole 6. The anti-kickback fingers are shown in phantom on Figure 2. There is a further hole 10 for the anti-kickback finger retaining pin.

The knife shown in Figure 2 has a blade 5 which depends from a gantry part 8 towards the table 2. The blade 5 tapers generally to a point towards the table. In this way a knife blade aperture, shown generally as x, is formed between a blade portion of the knife and the mounting part 3. The blade aperture is sized and configured to receive the edge of the table 2. In this way, a portion at the lower end of the blade 5 may, in some positions of the knife, extend below the level of the table through the saw blade aperture. In such positions the saw blade 9 is retracted such that the depth of blade above the table is reduced and there is sufficient space in the saw blade aperture to receive the tip of the knife blade.

As shown in Figure 1, the prior art riving knife may be raised by a small amount, by means of slot 4, to allow tilting of the riving knife with the saw blade. However, if the prior art riving knife is raised, a gap is formed between the bottom of the blade and the table surface.

This gap is shown generally as y.

The present invention allows replacement of an externally mounted riving knife of the prior art with a riving knife which conforms to the required European standard allowing the radial distance between the saw rim and the leading edge of the knife blade to be maintained within a predetermined range, for example, below 5 mm.

The adjustment is manual and the adjustment means is easily accessible to the user of the machine because it is external of the saw machine body. The substitution of the riving knife does not require redesign of any parts other than the knife itself and does not require any new parts for mounting the knife. In contrast, substitution of the prior art externally mounted knife with an internal knife, requires redesign of the table to accommodate the knife and redesign of the mounting means there for.

It will be noted that when the saw blade is positioned for maximum depth of cut, the saw blade almost fills the saw aperture in the saw table. However, when the saw blade is in a less than maximum cut depth position there is a greater distance between the rim of the saw blade and the edge of the saw blade aperture.

Now, because the riving knife of the present invention tapers from its lowest, narrow width to its highest, broader width then, at the almost maximum depth of cut saw blade position, the narrow tip of the riving knife can enter the small space not occupied by the saw blade in the saw blade aperture. As the saw blade is retracted to reduce the depth of cut, more and more of the riving knife width can be accommodated within the saw blade aperture. This is not the case with conventional internally mounted riving knives which are narrower at the tip than at the bottom.

Whilst an embodiment of the invention has been described, variations will suggest themselves to those skilled in the art which fall within the scope of the invention as defined by the appended claims. For example the riving knife of the invention may be mounted in any convenient manner and the saw blade may be a cutting disc.

Claims

1. A table saw riving knife adapted to be mounted externally of a table-mounted saw body in the plane of rotation of a table-mounted saw blade, the knife comprising a mounting part, a gantry part extending from said mounting part and arranged to be disposed above the surface of a saw table when the knife is mounted, a blade part depending from said gantry part towards said table, the riving knife being arranged so that the position of the blade part in the plane of rotation of the saw blade and with respect to said table can be manually adjusted to permit a curved leading edge of the blade part to be disposed proximate the arc described by the rim of the saw blade over the operative cutting height range of the saw blade.

2. A table saw riving knife as claimed in claim 1, wherein said blade part depends from said gantry part in the form of a finger tapering towards the table.

3. A table saw riving knife as claimed in claim 1 or 2, wherein the blade part is arranged in use to extend to the level of the table or below at all positions of the riving knife.

4. A table-mounted saw apparatus comprising a riving knife as claimed in any one of claims 1 to 3.

5. A table-mounted saw apparatus comprising a table having a saw blade aperture, a body supporting the table, a motor assembly for driving a blade mounted thereon and supported below the surface of the table, means for mounting a riving knife externally of said body, a riving knife having a blade part and means cooperating with said mounting means, and adjustment means whereby the position of the blade part in the plane of rotation of the saw blade can be manually adjusted to permit the blade part to be disposed with a curved leading edge thereof proximate the arc described by the rim of the saw blade over the operative height range of the saw blade.

6. A table-mounted saw blade apparatus as claimed in claim 5 or 6, wherein said riving knife comprises a mounting part comprising said means cooperating with said mounting means and a gantry part extending from said mounting part and disposed above the level of the table.

7. A table-mounted saw blade apparatus as claimed in claim 6, wherein said blade part of said riving knife depends from said gantry part in the shape of a finger tapering towards the table.

8. A table-mounted saw apparatus as claimed in claim 7, wherein the blade part is arranged to extend to the level of the table or below at all positions of the riving knife.

9. A table-mounted saw apparatus as claimed in any one of claims 5 to 8, wherein said mounting means and said means cooperating therewith, include said adjustment means.

10. A table saw riving knife as hereinbefore described with reference to Figure 2 of the accompanying drawings.