GB2361659A

GB2361659A - Cutter for forming polygonal holes

Info

Publication number: GB2361659A
Application number: GB0117233A
Authority: GB
Inventors: John Francis Collins; Roger Fields
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-10-25
Filing date: 2000-10-03
Publication date: 2001-10-31
Anticipated expiration: 2020-10-03
Also published as: GB2361659B; GB0117233D0

Abstract

A hole cutter 10 for forming a polygonal hole in masonry or the like to receive an electrical switch or socket box has a plurality of chisel blades 20 each releasably secured to a base 11 so that the blades 20 can be individually removed, e.g. for sharpening, or to replace a damaged blade. The blades 20 abut each other, preferably via chamfered lateral edges 24 in contact with one-another. The blades 20 are preferably received in a respective groove 19 in the base 11, and retained therein by a cap screw at 23. The blades 20 preferably include rounded recesses 21 to allow egress of material. A rotary cutter 15 preferably operates within the chisel blades 20.

Description

2361659 CUTTER FOR FORMING POLYGONAL HOLES This invention relates to a

cutter for forming polygonal holes and more particularly to an improved cutter for forming blind polygonal holes, such as rectangular or square holes, in masonry, brickwork and the like.

Known cutters of this kind have a box-like chisel extending from a base, the edges of the walls of the "box" remote from the base being sharpened. These box-like chisels are relatively expensive items and if any one of the cutting edges is damaged it is necessary to replace the chisel as a whole. Sharpening the cutting edges when they become blunt also presents a problem, so that there is an incentive to replace the chisel long before it is worn out.

In accordance with the present invention there is provided a cutter for forming polygonal holes in masonry and the like, comprising a base and chisel means defining at least the corners of the polygonal hole to be formed extending from one side of the base, the chisel means comprising a plurality of flat chisel blades each releasably secured to the base, each in abutment at its lateral edges with the two adjacent blades.

The blades may be engaged in respective grooves in the base and each blade may be releasably engaged in the respective groove by means of a grub screw penetrating the base.

Each blade preferably has chamfered side edges to abut with similar edges of contiguous blades.

The cutter may comprise a rotary cutter having a spindle which extends through and is rotatable relative to the base, means being provided for transmitting percussive blows to the blades through the base, and it is preferable that the circle swept by the rotary cutter is not less in diameter than the distance between parallel blades such that the rotary cutter acts on material to be cut in the interval between adjacent corners of the chisel means.

Said diameter is preferably approximately 5% greater than said distance between parallel blades.

2.

The blades may def ine at least the corners of a square hole to be formed.

Each blade may have in its 'cutting edge remote from the base a recess permitting passage of the rotary cutter.

The inner end of each said recess may be rounded.

Each said recess is preferably of depth sufficient to allow egress of cut material from the polygon defined by the chisel means between the rotary cutter and the base.

Each said recess preferably has a cutting edge continuing the cutting edge of the blade in which it is formed.

The base is preferably of greater cross-sectional area than the chisel means to limit the depth of the hole being cut.

A preferred embodiment of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: Figures 1 and 2 illustrate a cutter in accordance with the invention respectively in a partial exploded view and in an assembled condition, and Figure 3 is an underplan view of the cutter of Figures 1 and 2.

The cutter 10 illustrated comprises a square base 11 formed with a central aperture 12 through which a spindle 13 extends, the end 14 of the spindle being adapted to be engaged in the chuck of a hammer drill (not shown) and having fixed thereto below the base 11 a rotary cutter 15. Optionally the spindle 13 may also engage a drill bit 16 which in use will lead the rotary cutter 15. This will form a central pilot hole which may receive a plug, enabling a socket box to be screwed in position within the larger, square hole.

Radial arms of the rotary cutter 15 carry respective, oppositely facing carbide blades 16. The spindle 13 has a thrust ring 17 which in use will deliver percussive blows to a hardened anvil ring 18 secured to the upper side of the base 11.

3.

Slightly inward of and parallel with its sides the underside of the base 11 is formed with grooves 19 each of which receives a respective chisel blade 20. The blades are held in place in the grooves by cap screws penetrating holes 23 in the sides of the base 11. Each chisel blade 20 has a rounded recess 21 in its cutting edge 22, the cutting edge and its recess being continuously chamfered at approximately 45 degrees to the plane of the blade. In the assembled condition of the cutter 10 the blades 16 of the rotary cutter lie generally in the same plane perpendicular to the axis of spindle 13 as the cutting edges 22 of the chisel blades. The recesses 21 are of sufficient depth to provide gaps in the square formed by the blades 20 between the rotary cutter 15 and the underside of the base 11.

Each chisel blade 20 is also chamfered along its side edges 24 so that, as best seen in Figure 3, the blades 20 are in contact with one another throughout their thicknesses in the corners of the "box" formed by the blades.

Where it extends beyond its grooves 19 the peripheral region 25 of the underside of the base 11 serves as a stop limiting the depth of the square hole cut by the cutter 10.

In use whether or not a pilot hole is f irst drilled by the drill bit 16 the blades 16 of the rotary cutter and the chisel blades 20 will engage the wall or the like in which a square hole is to be f ormed more or less simultaneously. The base 11 will reciprocate as the rotary cutter 15 rotates so that as a circular hole is formed approximately of the same diameter as the width of the square hole to be formed simultaneously the tips of the chisel blades 20, spaced apart by the recesses 21, will f orm the corners of the hole. As the cutter sinks into the hole it is forming the cutting edges of the recesses 21 progressively cut the remainder of each side of the square from the corners inward toward the central cut made by the rotary cutter, until finally the whole of each chisel blade 20 is received into the wall.

In the meantime material cut by the rotary cutter 15 can escape from the "box" formed by the chisel blades 20 through the gaps between the rotary cutter and the base 11 defined by the recesses 21.

4.

Thus, although a large square hole is being made, the material being cut is not subjected to the action of chisel blade cutting edges as long as the sides of the hole at least until the hole is practically finished and in this way the damage e. g. to plaster surrounding the hole is minimised and clean, straight cuts are made.

As will be seen from Figure 3, the extremities of the blades 16 of the rotary cutter sweep a circle X to which the sides Y of the square hole being formed are substantially tangential, although it is found desirable that the diameter of this circle X should be slightly greater than the width of the hole so that a greater proportion of each side of the hole is cut by the rotary cutter 15 before the cut is completed by the respective chisel blade 20.

Claims

CLAIMS:

1 A cutter f or forming polygonal holes in masonry and the like, comprising a base and chisel means defining at least the corners of the polygonal hole to be formed extending f rom one side of the base, the chisel means comprising a plurality of f lat chisel blades each releasably secured to the base, each in abutment at its lateral edges with the two adjacent blades.

2. A cutter as claimed in claim 1, wherein the blades are engaged in respective grooves in the base.

3. A cutter as claimed in claim 2, wherein each blade is releasably engaged in the respective groove by means of a grub screw penetrating the base.

4. A cutter as claimed in any one of the preceding claims, wherein each blade has chamf ered side edges to abut with similar edges of contiguous blades.

5. A cutter as claimed in any one of the preceding claims and comprising a rotary cutter having a spindle which extends through and is rotatable relative to the base, means being provided for transmitting percussive blows to the blades through the base, wherein the circle swept by the rotary cutter is not less in diameter than the distance between parallel blades such that the rotary cutter acts on material to be cut in the interval between adjacent comers of the chisel means.

6. A cutter as claimed in claim 5, wherein said diameter is approximately 5% greater than said distance between parallel blades.

7. A cutter as claimed in claim 4 or claim 5, wherein the blades def ine at least the corners of a square hole to be f ormed.

8. A cutter as claimed in any one of claims 5-7, wherein each blade has in its cutting edge remote from the base a recess permitting passage of the rotary cutter.

6.

9. A cutter as claimed in claim 8, wherein the inner end of each said recess is rounded.

10. A cutter as claimed in claim 8 or claim 9, wherein each said recess is of depth sufficient to allow egress of cut material from the polygon defined by the chisel means between the rotary cutter and the base.

11. A cutter as claimed in any one of claims 8-10, wherein each said recess has a cutting edge continuing the cutting edge of the blade in which it is formed.

12. A cutter as claimed in any one of the preceding claim, wherein the base is of greater cross-sectional area than the chisel means to limit the depth of the hole being cut,

13. A cutter as claimed in claim 1 substantially as hereinbefore described with reference to and as shown in the accompanying Drawings.

12. A cutter as claimed in any one of the preceding claims, wherein the base is of greater cross-sectional area than the chisel means to limit the depth of the hole being cut.

Amendments to the claims have been filed as follows CLAIMS:

1. A cutter for f Orming polygonal holes in plaster, brickwork or masonry, comprising a base and chisel means defining at least the corners of the polygonal hole to - be formed extending f rom one side of the base, the chisel means comprising a plurality of f lat chisel blades each releasably secured to the base, each in abutment at its lateral edges with the two adjacent blades.

4. A cutter as claimed in any one of the preceding claims, wherein each blade has chamfered side edges to abut with similar edges of contiguous blades.

5. A cutter as claimed in any one of the preceding claims and comprising a rotary cutter having a spindle which extends through and is rotatable relative to the base, means being provided for transmitting percussive blows to the blades through the base, wherein the circle swept by the rotary cutter is not less in diameter than the distance between parallel blades such that the rotary cutter acts on material to be cut in the interval between adjacent corners of the chisel means.

7. A cutter as claimed in claim 4 or claim 5, wherein the blades def ine at least the corners of a square hole to be formed.

9 9. A cutter as clair,--,., in claim 8, wherein the inner end of each said recess is rounded.

10. A cutter as claimed in claim 8 or claim 9, wherein each said recess is of depth sufficient to allow egress of cut material from the polLygon defined by the chisel means between the rotary cutter and the base.

11. A cutter as claimed in any one of claims 8-10, wherein each said recess has a cutting edge continuing the cutting edge of the blade in which it is f ormed.