| 1. | A device for cutting a square or rectangular hole through a panel, comprising first and second parallel curved cutting blades spaced from one another, to cut two parallel sides of the hole, third and fourth parallel curved cutting blades spaced from one another and arranged substantially at right angles to the first and second cutting blades, to cut the other two parallel sides of the hole, a gearing arrangement to connect a drive motor to shafts about which the cutting blades rotate to drive the cutting blades. |
| 2. | A device as claimed in claim 1, wherein the gearing arrangement is contained internally within a foursided mounting block and each cutting blade is carried by a drive shaft extending out from each side of the mounting block. |
| 3. | A device as claimed in claim 1 or claim 2 wherein the gearing arrangement enables the device to connect to a hand held electric drill and further comprises a shaft extending into the mounting block to connect the drill to the drive shaft of each cutting blade. |
| 4. | A device as claimed in any one of the preceding claims, the device further comprising a thrust plate or ring having an aperture through which the cutting blades are reciprocally movable when the thrust plate or ring is engaged against a panel, to assist in positioning the device to accurately cut a hole at a set location through the panel. |
| 5. | A device as claimed in claim 4 wherein the thrust plate is spaced from the cutting blades by two or more telescopic members on either side of the device and is spring biased towards a normal position in which the thrust plate or ring is spaced from the blades such that the cutting blades do not protrude through the aperture in the thrust plate or ring. |
BACKGROUND The present method of cutting the necessary holes in panels such as wallboards are varied but the most efficient means generally is using an electric jigsaw or similar reciprocating electrically-driven saw. However, this is a relatively slow process and also marking out errors are not infrequent.
SUMMARY OF THE INVENTION The present invention consists in a device for cutting a square or rectangular hole through a panel, the device comprising first and second parallel curved cutting blades spaced from one another, to cut two parallel sides of the hole; third and fourth parallel curved cutting blades spaced from one another and arranged substantially at right angles to the first and second cutting blades, to cut the other two parallel sides of the hole; a gearing arrangement to connect a drive motor to shafts about which the cutting blades rotate to drive the cutting blades.
BRIEF DESCRIPTION OF DRAWING Preferred forms of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a three quarter perspective view of the device attached to a hand drill; Figure 2 is a side view of the device of Figure 1 before commencing cutting; Figure 3 is a side view of the device of Figures 1 and 2 in use against a panel during cutting;
Figure 4 is a cross section through one form of the device; Figure 5 is a cross section through another form of the device; Figure 6 is a cross section through a further form of the device; and Figure 7,7b and 7c are schematic plan views of different arrangements of cutting blades of the device.
DETAILED DESCRIPTION OF PREFERRED FORMS Figure 1 illustrates one preferred form of the hole cutting device 2. The device as shown is provided with first and second curved cutting blades 4,6 mounted on drive shaft 8 and third and fourth curved cutting blades 10,12 mounted on drive shaft 14. The cutting blades 4,6, 10,12 may be formed as circular saw blades as shown in Figure 1.
Alternatively, the cutting blades may be formed as elliptical saw blades (not shown) or as cross-shaped blades (not shown) having cutting tips which when rotated describe circles or ellipses. It will be appreciated that in this situation appropriate timing would be required.
The first and second blades 4,6 are spaced apart from one another along drive shaft 8 and are arranged in planes parallel to each other. Third and fourth blades 10,12 are spaced apart from one another along drive shaft 14 and arranged in planes parallel to each other. The third and fourth blades 10,12 are arranged substantially at right angles to the first and second blades 4,6.
As shown in Fig 1, circular cutting blades 4,6 and 10,12 are mounted on drive shafts 8 and 14 respectively. In one form of the invention the blades are mounted substantially near the centre of each blade. In another form of the invention, one or more of the blades could be mounted eccentrically to increase the length of the cuts. It will be appreciated that in this situation appropriate timing would be required.
The device 2 may be provided with a shaft to which a drive motor 18 may be connected. In a preferred form the shaft is housed in barrel 16 which may be connected to a hand held electric drill functioning as a motor 18. A fastener or clasp 19 may be fitted to barrel 16 to ensure a snug and secure fit. The shaft connects the drill 18 to the saw blades 4,6, 10,12 as will be further described.
Rotation of the shaft by the drill 18 causes drive shafts 8 and 14 to rotate which in turn causes blades 4 and 6 to rotate about shaft 8 and blades 10 and 12 to rotate about shaft 14.
It will be appreciated that the device could include the blades 4,6, 10,12 and motor 18 in a moulded housing and could be either battery or mains operated.
The arrangement of the blades is such that they can be forced into a panel to cut a square or rectangular hole in the panel.
In a preferred form of the invention the device 2 may be provided with a plate or ring 20 to assist in positioning the device 2 to accurately cut a hole at a set location through the panel. As shown in Figure 1 the plate 20 is provided with an aperture 22. The aperture 22 is sized so that the blades are reciprocally movable within the aperture 22 when the thrust plate 20 is engaged against a panel as will be further described.
It is envisaged that the blades could be positioned to permanently protrude through aperture 22. In a more preferred form, the blades are spaced from the plate 20 so that in a normal position the blades do not protrude through the aperture 22 and plate 20. During operation of the device the blades are able to be forced through the aperture 22 but are spring biased towards the normal position.
As shown in Figure 1, the plate 20 may be provided with notches 24. The notches 24 are for assistance in positioning the device 2 to cut a hole in a panel in the desired location. The user selects the desired location in which to cut a hole in the panel and may mark it with orthogonal pencil lines. The notches 24 may be positioned along these lines to ensure the correct positioning and orientation is obtained.
The preferred form of device 2 is shown in use in Figure 2. The device 2 is positioned in an appropriate position with plate 20 flush against the panel 24. In a preferred form the blades 4,6, 10 and 12 (6 not shown) are spaced from the panel by telescopic rods 26. As shown in Figure 2 the thrust plate 20 is biased by springs 28 towards a normal rest position in which the blades do not protrude through the aperture 22 in the thrust plate 20.
As shown in Figure 2, the preferred form of the device 2 is provided with a four- sided mounting block 30 within which drive shafts 8 and 14 rotate. The telescopic rods 26 may be mounted on thrust plate 20 and protrude through flanges 32 extending from mounting block 30. In the preferred form of the invention, two telescopic rods 26 are mounted on thrust plate 20, each of the rods on opposing edges of the thrust plate 20. Alternatively, the rods 26 could be mounted on opposed comers of the plate 20. Four rods 26 could be used, one on each comer of the plate 20.
The drill 18 is pressed by the user toward the panel 24, causing telescopic rods 26 to contract as shown in Figure 3. As rods 26 contract, the blades are brought toward and through panel 24. It will be appreciated that the device 2 may be fitted with dust extraction means (not shown). Once pressure by the user is taken off, the telescopic rods 26 expand, causing the blades to travel out of and away from the panel 24.
The device 2 may include a gearing arrangement to connect the drill 18 to the drive shafts 8 and 14. One form of gearing arrangement is shown in Figure 4. Drive shaft 14 is formed as two half shafts 14A and 14B. Blades 10 and 12 are mounted on shafts 14A and 14B respectively. The end of each shaft 14A and 14B inside mounting block 30 terminates in bevel gears 34.
Shaft 36 terminates at one end in a bevel gear 38 engaging bevel gears 34. Shaft 36 terminates at its remote end within barrel 16 in a gear 40 engagable with shaft 41 of the motor. As drill 18 rotates shaft 36, this in turn rotates half shafts 14A and 14B.
Shaft 8 extends through mounting block 30 at right angles to shafts 14A and 14B, terminating at each end in blades 4 and 6 (not shown). Positioned along the length of shaft 8 is a further bevel gear (not shown) engagable with bevel gear 38 so that shaft 8 rotes with shaft 36.
Figure 5 shows another preferred form of gearing arrangement for the device 2.
Blades 10 and 12 are mounted on shafts 14A and 14B respectively as described above with reference to Figure 4. Each of shafts 14A and 14B terminate in bevel gears 34. Mounted on shaft 14A is a cog wheel 40 or similar gearing engagable with further cog wheels 42 and 44. In a preferred form the cog wheel 44A is mounted on the rotating shaft 46 of a drive motor 42. Rotation of shaft 46 causes shaft 14A to rotate through engagement of cog wheels 40,42 and 44.
Shaft 8 extends through mounting block 30 at right angles to shafts 14A and 14B and operates in the same way as described above with reference to Figure 4.
Another form of gearing arrangement is shown in Figure 6. It operates in the same way as described above with reference to Figure 5 with the exception that a toothed belt 50 connects cog wheel 40 mounted on shaft 14A to cog wheel 44 mounted on shaft 46.
It will be apparent that the bevel gearing arrangement of Figures 4,5 and 6 could be replaced by other suitable gearing, for example worm gears or spiral bevel gears.
It is envisaged that the diameters and orientation of the blades may be selected most suitable for local conditions. For example, in New Zealand, a single flush box requires an aperture to be cut in the panel approximately 90mm by 55mm. In this situation blades 4 and 6 would be used to cut out the longer sides of the hole, and blades 10 and 12 the shorter sides, as illustrated in Figure 7A. In the preferred arrangement, as shown in Figure 7A, blades 10 and 12 overlap blades 4 and 6.
Alternatives are shown in Figure 7B in which blades 4 and 6 overlap blades 10 and 12 and 7C in which the blades do not overlap. Figure 7D shows an alternative arrangement used to cut square holes.
Although the cuts in the panel do not intersect, the portion of the panel bounded by the cuts may be knocked out, depending on the fragility of the material of the panel. From what has been described above it can be seen that a hole cutting device is able to be provided in a number of ways, each of which is comparatively simple, to facilitate the cutting of square or rectangular holes in panels.
As a measure of the efficiency of the device, it takes about 6 seconds to cut an aperture in 9mm or 12mm plaster board, whether reinforced with fibre-glass mesh or not. This provides a considerable time advantage over methods currently used, and also provides a better job in the sense that it is neater, does not damage the exit side of a panel and provides an aperture of the correct dimensions.
The foregoing describes the invention including preferred forms thereof.
Alternations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof, as defined in the accompanying claims.
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