GB2449943A

GB2449943A - Cutting implement with opposing knife and saw toothed edges

Info

Publication number: GB2449943A
Application number: GB0711185A
Authority: GB
Inventors: John Ridgeway Mainwaring
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-06-09
Filing date: 2007-06-09
Publication date: 2008-12-10
Also published as: GB0711185D0

Abstract

The cutting implement 10 comprises an elongate blade 12 and a handle 14 at a proximal end 15 of the blade. The blade 12 has opposed cutting edges 12, 20. One of the cutting edges 16 is formed with saw teeth 18 and the other cutting edge 20 is a knife edge. The handle 14 is arranged to permit the implement to be held and used with either edge 16, 20 facing down. Preferably the blade includes apertures 36. Preferably the serrated edge 16 is straight and the scalloped (28, 30, figures 1, 2) cutting edge 20 is curved. The blade cuts matted fibrous insulation, foam rubber pipe-wrap, sides of insulation boards and thinner sizes of substantially rigid foamed insulation board without producing crumbs, and thicker boards of substantially rigid foamed insulation material.

Description

TITLE

Cutting implement for thermal insulation material and method of manufacture thereof

DESCRIPTION

This invention relates to the cutting of thermal insulation material.

The thermal insulation of buildings is important, and various forms of insulation material are commonly used. For example, boards of substantially-rigid foamed insulation material, usually with metallic foil facings, and typically having a thickness of at least 100 mm are embedded in solid concrete floors and sometimes between floor or roof joists. Similar boards, but with a thickness typically of 50 mm, are used to fill cavity walls, or alternatively bats of matted fibrous insulation material, such as mineral wool, are used for this purpose.

Matted fibrous insulation material, such as glass fibre or mineral wool, is also used to fill the spaces between ceiling joists. Foam rubber or glass fibre matting is used to wrap pipes.

The matted fibrous insulation materials are typically cut to size with a long-bladed knife, for example resembling a carving knife. If the material is cut oversize, it can usually be squashed into place. A long-bladed knife can also be used to cut thinner boards of the substantially-rigid foamed insulation material. However, with the thicker boards, the knife tends to be pinched by the sides of the cut and jam. The thicker boards are therefore usually cut with a conventional saw. Accordingly, somebody who works with both materials needs to have two cutting tools. When cutting substantially-rigid foamed insulation boards, a saw produces waste in the form of crumbs, rather than dust, as the saw cut proceeds, and the waste becomes charged with static electricity as a result of the cutting action and tends to stick to wherever it lands. A mess is produced, which is difficult to tidy up. If the board is cut oversize and an attempt is made to force it between, say, a pair of joists, the integrity of the edge of the board can be destroyed. If, on the other hand, the edge of the board is trimmed to size with the saw which is to hand, first, even more statically-charged waste is produced and, second, a very ragged edge can be produced because the board material is not properly self-supported to both sides of the trimming saw cut as the cut proceeds.

One aim of the present invention, or at least of specific embodiments of it, is to provide an implement for cutting insulation materials which takes into account at least some of the problems described above. Another aim of the present invention is to provide an improved method of manufacture of a cutting implement.

In accordance with a first aspect of the present invention, there is provided a cutting implement for insulation material, comprising an elongate blade and a handle at a proximal end of the blade, the blade having opposed cutting edges, one of the cutting edges being formed with saw teeth and the other cutting edge being a knife edge, and the handle being arranged to permit the implement to be held and used with either edge facing down. A single implement is therefore conveniently provided having both a knife edge that can be used to cut layers of matted fibrous insulation material, foam rubber pipe-wrap and also the thinner sizes of substantially-rigid foamed insulation material without producing saw waste, and a saw edge that can be used to cut thicker boards of substantially-rigid foamed insulation material. The knife edge can also be used to trim or shave the side of such boards if they have been cut slightly over-size, without producing saw waste and without damaging the integrity of the remaining edge of the board.

The saw edge is preferably generally straight so that a uniform sawing action can be produced. However, the knife edge preferably curves, as viewed from the side of the blade, so that the width of the blade narrows towards its distal end, and so that a sweeping, swinging, slicing action can be employed which facilitates the making of long cuts.

The length of the blade between its distal end and the handle is preferably at least inches (254 mm) and more preferably 12 inches (305 mm). The maximum width of the blade is preferably between about 1" and 2" inches (38 mm and 64 mm), and more preferably about 2 inches (51 mm). The blade preferably has a thickness of between about 19 SWG and 16 SWG (1. 0mm and 1.6 mm), and more preferably about 1.5 mm.

In order to provide a good sawing action through boards of substantially-rigid foamed insulation material, the saw teeth preferably have an inverse pitch of between 6 and 10 points (5 and 9 teeth per inch; 200 and 350 teeth per metre), and more preferably about 8 points (7 teeth per inch; 280 teeth per metre).

As with a conventional saw, the teeth may have a set, i.e. alternate teeth are inclined laterally in opposite directions so that the kerf produced by the blade is greater than the blade thickness, reducing the tendency for the blade to be pinched when the workpiece is in compression and also enabling greater control over the direction of cut, e.g. to keep the cut on line. However, the teeth are preferably devoid of any significant set, or have a set that is less than conventional, for example 8 thou (0.2 mm) each way. The boards which the saw edge is intended to cut can usually be arranged so that they are not in compression when being cut, so that pinching is not a problem when sawing. Also, the boards have sufficiently flexibility to enable the cut to be kept on line without the need for any significant set. The lack of any set reduces the kerf width and the amount of saw-waste produced. Furthermore, the Omission of any significant set avoids the saw teeth damaging the cut edges of thinner boards when the implement is used as a knife. The blade preferably has a series of perforations therethrough spaced apart along its length. In the case where saw waste is not carried from the cut in the gullets of the saw teeth, but instead fmds its way between the faces of the blade and the cut material, the perforations provide space into which the waste can collect and be carried from the cut, so as to reduce the tendency of the blade to stick. The saw teeth are preferably arranged to cut with generally equal cutting action in both directions. Sawing the boards with which the saw edge is intended to be used does not entail a great deal of effort. By employing a generally symmetrical saw tooth profile, the implement cuts well on the pull stroke in addition to the push stroke, so that the cutting rate is increased.

As with a conventional knife, the knife edge may be straight as viewed in the plane of the blade. However, the knife edge preferably undulates within the thickness of the body of the blade as viewed in the plane of the blade. It has been found that, when cutting matted fibrous insulation material, such a edge form improves the cutting effectiveness of the knife edge.

Preferably, the undulations have a pitch of between 3/8 inch and 3/4 inch (9.5 mm and 19 mm).

The blade preferably has a first series of scallops formed in one face of the blade adjacent the knife edge and a second series of scallops formed in the opposite face of the blade adjacent the knife edge and offset from the scallops of the first series. As is known from patent document GB322398 published in 1929, the scalloping of a knife blade can produce a strongly-supportecj razor-like edge. Although the blade is scalloped in GB322398, the resultant knife edge is straight. The scalloping may be used in the present invention to produce a straight knife edge following the teachings of GB322398, but more preferably is used to produce an undulating knife edge as described above. As with a conventional knife, the blade may be generally tapered in thickness towards the knife edge. However, in the case of a scalloped blade, apart from the scallops, the blade preferably has a uniform thickness so as to simplify manufacture.

A second aspect of the present invention extends to the use of a cutting implement of the first aspect of the invention, wherein the saw edge is used at least to cut boards of substantially-rigid foamed insulation material, and the knife edge is used at least to cut layers of matted fibrous insulation material.

In accordance with a third aspect of the invention, there is provided a method of manufacture of a cutting implement according to the first aspect of the invention, comprising the steps of: providing a blank for the blade from sheet material having a uniform thickness; forming the saw teeth along one edge of the blank; scalloping the opposite edge of the blank to form the knife edge; and affixing a handle to the blank. Preferably, the scalloping step is performed without any prior thinning of the blank towards the knife edge, so as to simplify the manufacturing process.

Specific embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figures 1 & 2 are opposite side views of one embodiment of cutting implement; Figures 3 & 4 are opposite edge views of the cutting implement of Figures 1 and 2; Figure 5 is an edge view, on an enlarged scale, of a portion of the blade of the cutting implement within the circle 5 shown in Figure 3, before fmal sharpening; Figures 6 & 7 are opposite side views of the portion of the blade shown in Figure 5; Figures 8-11 are slice views of the portion of the blade shown in Figure 5, taken along the section lines 8-8 to 11-11, respectively, in Figure 5; Figures 13-18 are similar to Figures 5 and 8 to 11, respectively, but after final sharpening.

Figure 19 is an edge view, on an enlarged scale, of a portion of the blade of the cutting implement within the circle 19 shown in Figure 3; Figure 20 is a side view of the portion of the blade shown in Figure 19; Figure 21 is similar to Figure 19, but showing a modification to the edge of the blade; Figures 22-27 are similar to Figures 5 and 8 to 12, respectively, but showing a modification; Figure 28-33 are similar to Figures 5 and 8 to 12, respectively, but showing a fkirther modification; Figure 34 shows the blade of Figures 29 to 33, but before grinding; Figures 35-36 are similar to Figures 1 and 2, respectively, but showing a modified implement; and Figure 37 is a view on an enlarged scale of the portion of the blade referenced 37 in Figure 36.

Referring to Figures 1 to 4, a cutting implement 10 comprises an elongate carbon-steel blade 12 and a moulded plastics handle 14 at its proximal end 15. The blade 12 has a length L of 305 mm, a width W at its widest part of 50mm and a thickness T of 1.5 mm. One edge 16 of the blade 12 is generally straight and is formed with a series of saw teeth 18. The other edge of the blade 12 is generally straight over about half of its length from the handle 14 and then curves generally quarter-elliptically to join the saw edge 16 at the tip 22 of the blade 12. Both sides 24,26 of the blade are formed with series of scalloped recesses 28,30 each opening to the edge 20 over an extent E of about 8 mm. The recesses 28,30 on each side 24,26 of the blade 12 have a pitch P of about 12 mm, and the recesses 28 in one side 24 of the blade 12 are staggered with respect to the recesses 30 in the other side 26 of the blade 12 by half that pitch, "P. As will be described in detail below, this results in the edge 20 being a knife edge that, as viewed in Figure 3, undulates within the thickness of the blade 10.

The blade 12 is manufactured by stamping out of a sheet of uniform thickness carbon-steel a blank corresponding to the outline of the blade 12 and a tang (not shown) that is moulded into the handle 14.

The basic form of the knife edge 20 is produced in the maimer that will now be described with reference to Figures 5 to 12. A grinding wheel 32, the outline of part of which is shown in Figures 5 and 8 is used to form the recesses 28,30. The grinding wheel 32 has a diameter of about 75 mm and a thickness which is greater than the extent E of each scalloped recess 28,30 at the knife edge 20. The cutting edge 34 of the grinding wheel is rounded, with a radius of curvature R of about 24 mm. Each recess 28,30 is fonned by advancing the grinding wheel 32 against the respective side 24,26 of the blade 12 until the depth D of the recess 28,30 is equal to the thickness I of the blade 12. As can be seen from Figures 5, 8 and 12, at the middle of each recess 28,30, this produces razor-like edge portions 20a to the blade 10.

However, as can be seen from Figures 5, 9 and 11, at the edge of each recess 28,30, the edge portions 20b are considerably blunter. By suitable choice of the dimensions of the radius of curvature R of the edge 34 of the cutting wheel 32, the thickness T of the blade 12 and the pitch P of the recesses 28,30, as can be seen from Figures 5 and 10, half way between a recess 28 in one side 24 of the blade 12 and the adjacent recess 30 in the opposite side 26 of the blade, edge portions 20c that are razor-like, or almost razor-like, can be produced. Once the basic form of the knife edge 20 has been produced, the edge 20 is sharpened with a steel or by lightly grinding with a further grinding wheel, so that the blunt edge portions 20b shown in Figures 9 and 11 and the possibly blunt portions 20c shown in Figure 10 become sharp as shown in Figures 15 to 17. Therefore, as shown in Figure 13, a sharp undulating edge 20 is produced.

The saw edge 16 is formed in the conventional manner, but, as shown in Figures 19 and 20, without any set to the teeth and with the teeth being symmetrical so that the rake angle A of the teeth is the same in both directions of cut. The rake angle may, for example, be 30 degrees, and the inverse pitch of the teeth may be 8 points (7 teeth per inch; 280 teeth per metre).

After the saw and knife edges 16,20 have been formed, the blade 12 may be heat treated in a conventional maimer, and the handle 14 is attached to the tang (not shown) of the blade 12.

The handle 14 may be preformed and attached to the tang, or it may be moulded onto the tang.

The handle 14 is symmetrical both as viewed from the sides 24,26 of the blade 12 and as viewed from the edges 16,20 of the blade 12, so that the handle 14 fits the hand identically whether the implement 10 is being used as a saw or as a knife. As shown in Figures 1 and 2, the handle has integrally-moulded quilon or guard portions 17, to reduce the risk of the user's hand inadvertently sliding up the blade 12.

It will be appreciated that many modifications and developments may be made to the embodiment of the invention described above.

For example, as shown the Figure 21, the teeth 18 of the saw edge may have a small amount of set.

Also, as shown in Figures 22 to 27, a modified grinding wheel 32 may be used to form the scalloped recesses 28,30 in the knife edge 20. Instead of being slightly wider than the extent E of the recesses 28,30 at the knife edge 20 as shown in Figures 1 and 6, the grinding wheel 32 is slightly wider than the pitch P of the recesses 28,30. Also, instead of the cutting edge 34 of the grinding wheel 32 being simply rounded, the cutting edge 34 is dressed so that it resembles half a cosine wave, generally following the shape of half an undulation in the finished knife edge 20. As a result, the edge 20 as initially ground lacks the blunt portions 20b shown in Figures 9 and 11, and less, or no, final sharpening of the knife edge 20 is required.

Also, as shown in Figure 34, the blade 12 need not be of uniform thickness T before the knife edge 20 is ground. Instead, it may taper from the thickness T to a thickness T' at the edge. As a result, and as shown in Figure 28, the amplitude of the undulations in the knife edge is reduced from Tto T' The implement 10 shown in Figures 35 to 37 is similar to the implement 10 describej above except in the following respects. The straight portion of the knife edge 20 is parallel to the saw edge 18, rather than tapering towards it towards the proximal end 15 of the blade. A separate metal plate 17 is fitted to the tang of the blade 12 before the handle 14 is fitted in order to provide a quillion or guard. An arrangement of through-holes 36 is provided in the blade 12 to assist in carrying waste from the kerf when the implement 10 is being used as a saw. The holes 36 may be circular or any other appropriate shape and may have a diameter of, for example, 6 to 8 mm. As shown in Figures 35 and 36, the holes 36 are arranged in two rows which may be spaced apart by, for example, 12 to 15 mm. The holes 36 in each row may have a pitch of, for example, 25 mm, and may be staggered from the holes 36 in the other row. As shown in Figure 37, the teeth 18 of the saw edge 16 have a smaller rake angle than the teeth shown in Figure 20, and the points 38 of the teeth 18 may be chamfered alternately in opposite directions so that the points of the teeth are not unduly weakened.

It should be noted that the embodiments of the invention have been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention.

Claims

(The reference numerals in the claims are no: i'uended to limit the scope of the claims.) 1. A cutting implement (10) for thermal insulation material, comprising an elongate blade (12) and a handle (14) at a proximal end (15) of the blade, the blade having opposed cutting edges (16,20), one (16) of the cutting edges being fonned with saw teeth (18) and the other cutting edge (20) being a knife edge, and the handle being arranged to pennit the implement to be held and used with either edge facing down.
2. A cutting implement as claimed in claim 1, wherein the saw edge is generally straight.
3. A cutting implement as claimed in claim 1 or 2, wherein the knife edge curves, as viewed from the side of the blade, so that the width of the blade narrows towards its distal end (22).
4. A cutting implement as claimed in any preceding claim, wherein the length (L) of the blade between its distal end and the handle is at least 250 mm.
5. A cutting implement as claimed in claim 4, wherein the length of the blade is about 305 mm.
6. A cutting implement as claimed in any preceding claim, wherein the maximum width (W)ofthebladeisbeenabout38mmandM
7. A cutting implement as claimed in any preceding claim, wherein the blade has a thickness (1) of between about 1.0 mm and 1.6 mm.
8. A cutting implement as claimed in any preceding claim, wherein the saw teeth have a inverse pitch of between 200 and 350 teeth per metre.
9. A cutting implement as claimed in any preceding claim, wherein the teeth have a set.
10. A cutting implement as claimed in any of claims I to 8, wherein the teeth are devoid of any significant set.
11. A cutting implement as claimed in any preceding claim, wherein the blade has a series of perforations (36) therethrough spaced apart along its length.
12. A cutting implement as claimed in any preceding claim, wherein the saw teeth are arranged to cut with generally equal cutting action in both directions.
13. A cutting implement as claimed in any preceding claim, wherein the knife edge is straight as viewed in the plane of the blade.
14. A cutting implement as claimed in any of claims 1 to 12, wherein the knife edge undulates within the thickness of the body of the blade as viewed in the plane of the blade.
15. A cutting implement as claimed in claim 14, wherein the undulations have a pitch (P) of between 10 mm and 20 mm.
16. A cutting implement as claimed in any preceding claim, wherein the blade has a first series of scallops (28) formed in one face (24) of the blade adjacent the knife edge and a second series of scallops (30) formed in the opposite face (26) of the blade adjacent the knife edge and offset from the scallops of the first series.
17. A cutting implement as claimed in any preceding claim, wherein the blade is generally tapered in thickness towards the knife edge.
18. A cutting implement as claimed in claim 16, wherein, apart from the scallops, the blade has a uniform thickness.
19. A cutting implement for thermal insulation material substantially as described with reference to the drawings.
20. The use of a cutting implement as claimed in any preceding claim, wherein the saw edge is used to cut boards of substantially-rigid foamed insulation material, and the knife edge is used to cut layers of matted fibrous insulation material.
21. A method of manufacture of a cutting implement as claimed in claim 18, comprising the steps of; providing a blank for the blade from sheet material having a uniform thickness; forming the saw teeth along one edge of the blank; scalloping the opposite edge of the blank to form the knife edge; and affixing a handle to the blank.
22. A method as claimed in claim 21, wherein the scalloping step is performed without any prior thinning of the blank towards the knife edge.

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23. A method of manufacture of a cutting implement, substantially as described with reference to the drawings.