Field of the Invention
[0001] The present invention relates generally to core drills, and more particularly but
not necessarily to core drills of the type having diamond or other abrasive cutting
members for use in cutting masonry and stone.
Background of the Invention
[0002] Core drilling of different materials requires different types of cutting tools. However,
due to the nature of the cutting process some problems facing these cutting tools
are similar.
[0003] A generic core-cutting tool 1 is shown in Figures 1 and 2. In operation the core
tool is attached, via connecting means 4, to a machine, which acts as a driving source,
typically a drill. As the core-cutting tool is rotated the cutting elements 2, which
are mounted on the tubular support body 3, impart a cutting action upon the chosen
material e.g. stone, thus creating a hole in the said material; hereinafter referred
to as the work piece. As the core-cutting tool is worked, it moves into the hole being
cut in the work piece thereby maintaining the cutting force imparted on the work piece.
[0004] It is therefore standard practice for the cutting elements to be arranged so as to
cut a hole in the work piece that is of sufficient size to receive the tubular support
body as the core-cutting tool moves into the hole. The size difference between the
radius of the tubular support body, and the radius of the hole cut by the cutting
elements is known as the side clearance δ.
[0005] The size of the side clearance has a noticeable effect on the functionality of a
core-cutting tool. A large side clearance will allow the tubular support body to enter
the hole with a minimised likelihood of jamming. However, the resulting increased
width of the cutting elements means that more material has to be removed, which leads
to longer cutting times, slower penetration and the need for an increased level of
feed pressures all of which in turn lead to increased machine wear and operator fatigue.
[0006] Alternatively, a small side clearance provides a much easier cut due to the smaller
amount of material being removed. However, although the cutting is easier, the likelihood
of jamming and/or snagging is greatly increased, which causes a severe safety hazard.
[0007] Jamming and stalling can burn out the machines or their clutches and/or severely
injure the operator if the clutch of the machine does not work efficiently. Jamming
can also be hazardous if the machine is too powerful for the operator to hold when
the tool has jammed. Repeated jamming can lead to wear on the tubular support body,
and/or deformation of the tubular support body due to overheating. Side wear and abrasion
are also caused by repeated jamming.
[0008] It is generally accepted that the side clearance is relatively large to minimise
the likelihood of jamming.
[0009] Due to the high stresses involved in the cutting of certain materials, wear on the
cutting elements is commonplace. As a result of such wear the size of the side clearance
of the core-cutting tool can be reduced, thus leading to the problems discussed above.
Summary of the Invention
[0010] Accordingly, the invention provides a core-cutting tool comprising: a tubular support
body having connection means for connection to drive means and, arranged on one end
thereof, an annulus of cutting elements; characterised in that the inner and/or outer
surface of the tubular support body comprises at least one abrasive element, positioned
between the connection means and the annulus of cutting elements, which does not extend
radially beyond the cutting extent of the annulus.
[0011] It will be understood from the invention that when jamming occurs, the arrangement
of at least one abrasive element on the support body will permit the core-cutting
tool to cut itself free and thereby minimise the safety hazards discussed above. The
reduction in jamming will also reduce the wear and deformation caused to the core-cutting
tool.
[0012] It may be of advantage for the support body to comprise a plurality of abrasive elements
on the inner and/or outer surface of the tubular support body.
[0013] Preferably, the abrasive elements will be attached to the support body by welding,
soldering, gluing or the like. It will be appreciated from the invention that alternative
fixing methods may be used, such as screw attachment.
[0014] In the preferred embodiment, the abrasive elements comprise further cutting elements.
[0015] Preferably, both the cutting elements and the further cutting elements may be those
suitable for cutting stone and masonry, such as diamond matrix or silicon carbide.
However, it will be appreciated from the invention that when alternative cutting elements
are used, such as those used in wood cutting, that the abrasive element(s) may comprise
a simple roughened surface like sand paper or a metal file.
Brief Description of the Drawings
[0016] In the drawings which illustrate both the prior art and the preferred embodiments
of the invention:
Figure 1 shows a diagrammatic representation of the side view of a generic core-cutting
tool from the state of the art;
Figure 2 shows a diagrammatic representation of the bottom plan view of the tool shown
in Figure 1:
Figure 3 shows an elevational side view of a first preferred embodiment of the invention;
Figure 4 shows a bottom plan view of the embodiment of Figure 3;
Figure 5 shows an elevational side view of an second preferred embodiment of the invention;
Figure 6 shows a bottom plan view of the embodiment of Figure 5;
Figure 7 shows an elevational side view of an alternative preferred embodiment of
the invention;
Figure 8 shows a bottom plan view of the embodiment of Figure 7;
Figure 9 shows an elevational side view of a further alternative preferred embodiment
of the invention.
Detailed Description of the Illustrated Embodiments
[0017] Figure 3 shows a core-cutting tool with a first set of cutting elements 2 arranged
on one end of the tubular support body 3. It will be appreciated from the invention
that the type of cutting element used depends upon the material being tooled. At the
opposite end of the tubular support body 3 is arranged connection means 4 to permit
the tool to be connected to a drive source, such as a power drill or the like.
[0018] A second set of cutting elements 5 are arranged radially around the sidewalls of
the tubular support body 3. The side cutting elements can be attached in many ways,
such as welding, soldering and gluing. Other methods of attachment include electroplating
and even screw fixing. It is also appreciated that, alternatively, the sidewalls themselves
may be adapted to provide the abrasive element(s) in a manner similar to a metal file,
for example having rasps.
[0019] It is understood that the second set of cutting elements could be made from a similar
material as the first set of cutting elements, although this does not have to be the
case.
[0020] Both sets of cutting elements exert a cutting force, the first set cuts into the
work piece and the second set prevents snagging of the tubular support body 3 within
the work piece by cutting itself free of any obstacles that could cause snagging.
[0021] The second set of cutting elements 5 comprise a collection of elements with triangular
shaped plans, arranged in rows around the circumference of the tubular support body
3. However, it is appreciated that different shaped cutting elements such as those
with rectangular plans and circular plans, may be used.
[0022] It is also appreciated that alternative arrangements of the elements may be of benefit.
One alternative arrangement would be to arrange adjacent rows of elements so that
elements in one row are next to the spaces between the elements in an adjacent row.
[0023] Possible benefits could be gained by using an arrangement comprising a combination
of cutting elements of different shapes.
[0024] From Figure 4 it can better be understood how the second set of cutting elements
5, extend radially from the tubular support body 3. It can also be appreciated that
the second set of cutting elements 5 do not extend beyond the first set of cutting
elements 2. Although the second set of cutting elements 5 only extend outwards in
the figure, it is appreciated that they may extend radially inwards instead. It is
also appreciated that a combination of cutting elements extending radially, both outwards
and inwards, may have further advantages.
[0025] Figure 5 shows a second preferred embodiment of the invention. In this embodiment
the tubular support body 3 has a slit 6 in a sidewall thereof. It is understood in
the art that such slits are beneficial as they provide, amongst other things, ventilation
to the core-cutting tool thus minimising heat build up, which can lead to tool deformation.
It will be appreciated that slits of different dimensions will have equal merit.
[0026] In Figure 5 a second set of cutting elements 7 are arranged on the leading edge of
the slit 6, so that as the tool rotates the cutting elements 7 exert a cutting force
on any obstacles that may cause snagging or jamming. The cutting elements 7 also protect
the slit 6 from wear caused by said obstacles and because the slit 6 can be a area
of weakness in the tool this protection is beneficial.
[0027] It will be understood that different arrangements of cutting elements can make up
the second set of cutting elements 7. Due to the improved protection afforded to the
slit 6, it may be possible for a core-cutting tool to have more than one slit, thus
providing the associated benefits without greatly impairing the structural integrity
of the tool.
[0028] Figure 6 shows the positioning of the second set of cutting elements 7 within the
slit 6.
[0029] Figure 7 shows an alternative embodiment of the invention, wherein the layer of abrasive
material 8 is attached to the outer wall of the tubular supports structure 3. The
abrasive material would preferably be glued to the supports structure, but it is appreciated
that alternative fixing methods would be equally viable. It is appreciated that the
type of abrasive material used depends on the type of material being worked by the
tool.
[0030] Typically a coating of diamond matrix or silicon carbide would be used with masonry
or stone. Whereas with timber, a less resilient abrasive material, such as sandpaper,
glasspaper or the like, could be used.
[0031] In Figure 8 it can be seen that in this preferred embodiment, a coating of abrasive
material 8 is attached to both the inner and outer surfaces of the tubular support
structure sidewall. Alternatively, a coating of abrasive material 8 may be present
on only one of the surfaces of the support structure sidewall.
[0032] Whereas in the embodiment shown in Figures 7 and 8 the entire surface of the support
structure sidewall may be covered in abrasive material, it is appreciated that only
selected areas may be covered in an abrasive material. Figure 9 shows an embodiment
where abrasive material only covers a section 9 of the sidewall. Any number of different
shaped sections 9 could be used as is required.