SAW JIG

Abstract: A saw jig in which a guide member (10) is clamped onto a board to be cut. The guide member has a slot (14) for guiding the saw blade for travel in a straight line. The guide member is clamped by means of clamping bolts and nuts onto a board to be cut and the corners of the slot (14) make contact with the surface of the board on order to prevent the board form chipping. The board is cut while lying in a near vertical position so that the cut woood does not place undue strain on the jig and does not separate before the cut has been completed.

Description: SAW JIG The present invention relates to a saw jig to assist in sawing of boards and finds particular application in the sawing of laminated board. Considerable difficulty may be experienced even by a skilled person when cutting wood and board accurately in a straight line. When cutting along a straight line, it is difficult to angle the saw correctly to be exactly perpendicular to the faces of the board. Furthermore, when the board is a laminate, the teeth of the saw tend to cause the laminate to part from its support on the exit side of the blade and it is this that is responsible tor the chipping and splintering. The present invention seeks to provide a saw jig which mitigates the above disadvantages and enables a clean cut to be made without damaging the surfaces of the board. In accordance with the present invention, there is provided a saw jig for cutting a board, which comprises a guide member defining a guide slot for a saw blade, the guide slot being of substantially the same width as the saw blade, and clamping means for securing the guide member on the blade exit side of the board, the corners of the guide member defining the slot being held by the clamping means in intimate contact with the surface of the board whereby to prevent chipping. When using a hand saw, the teeth are angled away from the user so that the chipping of the laminate board tends to occur on the undersurface of the board. On the other hand, with a circular saw the teeth are so angled as to pull the board against the circular saw with the result that the chipping tends to occur on the top surface. The term "exit side" of the board is that side at which chipping tends to take place being the side on which the saw leaves the board after performing a cutting stroke. In the present invention, the edges of the guide member for the saw press against the surface of the board which is prone to chipping or splintering and no separation of the laminate from the support board can take place beyond the line of contact between the guide member and the surface of the board. Though particularly intended for laminated boards, the inven tion may b e us ed wi th other boards prone, to chipping or splintering including chip board, f ibre board, hardboard, plywood and the term "board" as used herein is intended_ to include all such materials. In a preferred embodiment of the invention, guide members are provided both on the entry and exit side of the saw blade, the guide member on the entry side having a slot of the substantially the same width as the saw blade aligned with the s lot in the guide member on the exit s ide and ensuring that the blade remains in the desired plane relative to the surface of the board. The slot defining edges of the guide member on the exit side of the board may in time become damaged by the saw blade. It is therefore preferred that the guide members should have replaceable corner strips releasably secured to the body of the guide members. In order to ensure that the edges of the corner strips are urged into intimate contact with the board surface, it is desirable that the corner strips should be urged resiliently xn the direction of the board. This may, for example, be achieved by placing a foamed plastics layer between the guide member and the corner strips. In one embodiment of the invention, the corner strips may be formed of metal softer than the metal of the blade but it has been found, surprisingly, that a plastics strip is equally effective, causes no damage to the saw blade and is long lasting. The plastics corner strips or inserts may be retained on guide members made of any suitable material, for example the guide members may be formed of aluminium or plastics extrusions, or rolled steel section. Where the guide members are formed of an extrusion, the corner inserts may be formed with a bead received in a channel. In this case, the shape of the strip may be such that the slot defining edges lie spaced from the surface of the guide member, so as to be urged in the direction of the board surface. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partly exploded perspective view of a first embodiment in accordance with the invention, Figure 2 shows a detail of the saw jig in Figure 1 in perspective. Figure 3 is a plan view of the part of the saw jig shown in Figure 2, and Figure 4 shows an alternative construction of the guide members. The saw guide shown in Figs 1 to 3 comprises a first guide member 10 formed in two halves, designated 10a and 10b , respectively. The two halves are secured to one another at their upper and lower ends by set screws 31 OMPI and 30, respectively, shown in more detail in Figures 2 and 3. The upper ends of the guide member halves 10a, 10b are pivotably connected to a generally U-shaped stand 12, which folds flat when the jig is not in use. The two halves 10a and 10b of the guide member 10, when in. use, are spaced apart to define a slot 14 having a width equal to the thickness of the saw blade being used. The upper edges of the guide slot 14.are defined by a^pair of corner strips 32 which are also shown in more detail in Figure 2. The two halves of the guide member 10 are each provided with two clamping bolts 16, arranged one at each end of the respective guide member half, the bolts 16 being intended to receive clamping nuts 18. A second guide member 20, generally similar to the guide member 10, fits over the board 50 to be cut. The second guide member 20 is made of two halves 20a and 20b which are seperable from one another. The irst half 20a has holes 26 through which the clamping bolts pass during use, while the second clamping member half 22b has holes 28 which are elongated to form slots which allow lateral movement of the halves relative to one another after the bolts 16 have been passed through the holes 26, 28 but before the clamping nuts 18 have been secured. The clamping nuts 18 have conical seats 40 (see Fig 2) which engage in countersink recesses 42 at the mouths of the holes 26, 28 to ensure alignment of the slot 24 in the upper guide member 20 with the slot 14 on the lower guide member 10 when the clamping nuts 18 are tightened. Referring now to Figure 2, it is seen that generally L- shaped strips 32 of a plastics material are secured over the corners of the guide member halves 10a, 10b, 20a and 20b. The corner strips 32 may be secured to the guide members 10, 20 in any suitable manner such as by adhesive, screws or interlocking engagement. The surface of the corner inserts 32 facing the board 50 to be cut ? is not flush with the adjacent surface of the guide member so that when the clamping nuts are tightened on a board as shown in Figure 2, the edges of the inserts are firmly clamped against the board surfaces. If desired, a rib or the like projection may be formed on the surface of the guide member halves to ensure that the cut remains perpendicular to the board. The set screws 31, 30 pass through the upper and lower ends of the first guide member 10a and are screwed into the second guide member 10b. Springs 35 are provided about the screws 31, 30 to urge the two halves apsrt when the screws are slackened. By ajusting these screws the separation of the two guide member halves, that is to say the width of the guide slot, may be varied. The clamping nuts have heads 36 which are located in holes in the guide member 20. A cross bore drilled through the guide member and the heads of the clamping bolts receives a pin 38 to prevent rotation of the clamping bolts when the clamping nuts are tightened. The pin 38 also serves to align the two halves 10a, 10b. The same pin 38 also carries a freely rotatable overrun roller 51 (see Fig. 3} located within the guide slot so that after the saw has completed the cut through the board it causes the roller to slip on the pin 38 and prevents accidental damage to the saw jig. If desired, the surface of the roller 51 may be serrated to ensure that it rotates with movement of the saw and a click mechanism, similar to a rattl-e, may be driven by rotation of the same roller so that a clicking noise may indicate to the user that he has sawn through the entire width of the board. In order to use the saw jig, it is first set in the attitude shown in. Figure 1. The saw jig is intended to be used in the attitude illustrated, that is to say with the saw guide slot substantially vertical with the board leaning back at an angle preferably 70° to the horizontal. The separation of the two guide member halves 10a and 10b at the upper and lower ends is set to match the width of the saw blade cut by altering the set screws 30, 31 as necessary. The board 50 which is to be cut is next slid in position between the two guide members. To assist in this task, springs 37 arranged around the clamping bolts 16 urge the two guide members apart. It will be noted that the heads 36 of the lower clamping bolts 16 in Figure 1 are formed with a semi-circular stop 39 projecting into the gap between the two guide members, the purpose of the stops 39 being to support the board and prevent it from resting on the springs 37. After the board 50 has been inserted between the two guide members and brought to rest on the stops 39 of the lower clamping bolts, the bolts of the first upper guide -member half 20a are tightened to grip the board 50 loosely.- At this time, because the clamping nuts of the second half 20b of the guide member have not been tightened, the latter half 20b may be moved slightly aside, on account of the slotted holes receiving the clamping bolts, to allow the user to see clearly that the first guide member half 20a is accurately aligned with a line of cut which has been previously scribed on the board. It is now only necessary to tighten all the clamping nuts firmly to prevent any movement of the board and as the nuts for the second guide member half 20b are tightened ' the seating of the clamping nuts in the countersunk bores automatically ensures the spacing between the two halves of the guide member 20. In this condition there are defined aligned slots 14, 24 exactly at right angles to the surface of the board 50. The edges of the slots are in intimate contact with both the upper and the lower sudface of the board 50 so that the board 50 may be cut either by means of a hand saw or by means of an electrical saw without the risk of the surface on the exit side of the saw blade chipping. When a board is sawn while horizontal, it is necessary to provide clearance for the saw blade behind the board. It is also necessary to support the board firmly on both sides of the cut to prevent the board from breaking when nearing the end of the cut. The fact that the board is in a nearly vertical attitude reduces the risk of the board breaking into two pieces before the cut is completed as a result of the forces acting on the board. This also has the advantage that the jig is not subjected to the strain of supporting an unsupported horizontal cut length of board. In order to reduce the risk of the board separating prematurely still further, it is possible to provide feet for mounting on the board near its projecting ends so that no bending moment is applied along the cutting line. The hori zontal di spos i tion of the board of f ers the further advantages that less workspace is required and if the board i s wide there i s no need to lean i n an uncomfortable position over the board while sawing and c on s eque n t ly the us er of th e j i g need no t s u f f e r unnecessarily from fatigue. When the saw cut is complete, the saw engages the roller 51 lying beneath the lower edge of the board and this roller will commence to turn but will not be damaged by the s aw. A s earl i er descr ibed , the rol ler may be arranged to make a sound as it rotates to warn that the cut is complete. OMPI The corner strips 32 secured to the upper and the lower guide members are L-shaped plastics strips secured onto the body of the guide members. The longer limb of the "L" is chamfered at the top to guide the saw into the slot without damage to the strips 32. It has been found the a plastics material, such as PVC, is advantageous because it reduces the risk of the saw being worn by abrasion. Also, because the plastics material may itself wear slightly, the corner is permanently maintained sharp and makes contact with the surface of the board immediately adjacent the saw cut. It is alternatively possible, however, for the corner strips to be of metal. Furthermore, the corner strips need not be mounted directly on the guide members but a layer of foamed plastics material or a spring may be interposed to urge the strip resiliently in the direction of the board 50. The embodiment partially shown in Fig. 4 differs from the embodiment described above in so far as concerns the construction of the guide members. In Fig. 4, the guide member halves 60 are formed of an aluminium extrusion. In the upper left corner, as viewed, the extrusion is formed with a channel 62 which receives a bead 64 on the end of a limb 66 which is formed as an extension of the corner strip. The corner strip is extruded from a plastics material and in its free state will be spaced from the body of the guide member. As a result, the corner strip is urged resiliently against the board when the clamping muts 18 are tightened to ensure intimate contact with the surface of the board. Various modifications may be brought to the embodiments described above. In a first modification, parallel ribs may be formed on the guide member halves 20a, 20b to act as a guide for the sole plate of an electrical saw. It is ordinarily difficult to use a jig saw to cut a straight line but such ribs allow the jig to be used with most kinds of power saw. The clamping action in the described embodiments is not as effective if the board is considerably narrower than the distance between the clamping bolts 16. This is because the guide members would need to be very stiff to withstand bending. This problem may be overcome by placing a piece of waste board between the guide members 10, 20 or by means of a washer around the upper clamping bolts. As a further alternative, several holes may be provided along the length of the guide members so that the separation of the clamping nuts may be altered to suit the width of the board being cut.

Claims: CIAIMS 1. A saw jig for cutting a board, characterised by a guide member (10a, 10b) defining a guide slot (14) for a saw blade, the guide slot being of substantially the same width as the saw blade, and clamping means (16, 18) for securing the guide member (10) on the blade exit side of the board (50), the corners of the guide member defining the slot (14) being held by the clamping means (16, 18) in intimate contact with the surface of the board whereby to prevent chipping. 2. A saw jig as claimed in claim 1, wherein guide members (10, 20) are provided both on the entry and exit side of the saw blade, the guide member (20) on the entry side having a slot (24) of the substantially the same width as the saw blade aligned with the slot (14) in the guide member (10) on the exit side and ensuring that the blade remains in the desired plane relative to t e.-s rface of the board (5). 3. A saw jig as claimed in claim 1 or 2, wherein each guide member (10, 20) has removable corner strips (32). 4. A saw jig as claimed in claim 3, wherein the removable corner strips (32) are formed of a plastics material. 5. A saw jig as claimed in claim 3 or 4, wherein the corner strips (32) are mounted on the body of each guide member (10,20) in such a manner as to project resilien¬ tly beyond the surface of the guide member body. 6. A saw jig as claimed in any preceding claim, in which each guide member (10,20) is formed in two halves (10a,10b,20a,20b) separated form one another by the guide slot (14,24), the separation between the halves being adjustable so as to enable the use of saw blades of differing thicknesses. 7. A saw jig as claimed in claim 2 or any claim appended thereto, wherein the clamping means comprise bolts (16) secured to one guide member (10) and passing through the other guide member (20) and nuts (18) for clamping the guide members onto a board (50) arranged between the two guide members. 8. A saw jig as claimed in claim 7 as appended to claim 6, wherein the holes * in at least one guide member half (20b) are elongated into slots so as to allow lateral movement of the halves of a guide member relative to one another prior to tightening of the clamping bolts. - 9. A saw jig as claimed in claim 7 or any claim appended thereto, wherein the clamping nuts have a conical seat and the holes in the guide member is countersunk so as to allow automatic alignment of the guide members on opposite sides of the board (50) being cut. 10. A saw jig as claimed in any preceding claim, in which a stand (12) is provided to support the jig with the board being cut in a plane inclined at a small angle to the vertical. 11. A saw jig as claimed in claim 10, wherein the stand (12) is generally U-shaped and pivotably connected to one guide member (10), whereby the jig may fold flat. 12. A saw jig as claimed in any preceding claim, wherein each guide member is in the form of an extrusion (60). 13. A saw jig as claimed in claim 12, in which the extrusion includes a channel (62) adjacent one corner thereof, and a removable corner strip is formed as a second extrusion having a -bead (64) received within the channel (62).

Inventors: BLAINE ANTHONY FREDERICK, BLAINE, ANTHONY, FREDERICK
Applicants: PRUTEC LTD, PRUTEC LIMITED
Application year: 1983
Main classification: B27G19
IPC codes: B27G5, B27G19