US3585980A

US3585980A - Method and device for removing mortar or the like from between superimposed rows of bricks or the like

Info

Publication number: US3585980A
Application number: US805960*A
Authority: US
Inventors: Fred Mellor
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-09-03
Filing date: 1969-02-20
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22

Abstract

A method of removing mortar from between the rows of superimposed bricks while collecting the dust generated thereby and a blade guard for a grinding disc with a tangential dust outlet.

Description

United States Patent Inventor Appl. No. Filed Patented METHOD AND DEVICE FOR REMOVING MORTAR OR THE LIKE FROM BETWEEN SUPERIMPOSED ROWS'OF BRICKS OR THE LIKE 11 Claims, 5 Drawing Figs.

US. Cl. 125/13, 51/268, 51/273, 51/283 Int. Cl B2841 l/04, B24b 55/04, B24b l/00 Field of Search 51/170,

[56] References Cited UNITED STATES PATENTS 3,034,493 5/1962 Bandy 125/ 1 3 2,562,396 7/1951 Schutz 143/159 2,328,244 8/1943 Woodward 143/41 2,789,404 4/1957 Downing 51/273 1,888,679 11/1932 Knapp 143/159 UX FOREIGN PATENTS 1,280,025 11/1961 France 51/273 1,231,379 4/1960 France 51/273 1,121,968 1/1962 Germany 51/273 848,564 9/1960 Great Britain 51/273 Primary Examinerllarold D. Whitehead Attorney-Shoemaker and Mattare ABSTRACT: A method of removing mortar from between the rows of superimposed bricks while collecting the dust generated thereby and a blade guard for a grinding disc with a tangential dust outlet.

PATENTEU JUN22 IQYI 3; 5 5, 9

' sum 1 or 2 INVENTOR FRED MELLOL PATENIEU JUN22 nan SHEET 2 [IF 2 INVENTOR FRED MELLOR BY 9 AAA/1 ATTORNEYS METHOD AND DEVICE FOR REMOVING MORTAR OR THE LIKE FROM BETWEEN SUPERIMPOSED ROWS OF BRICKS OR THE LIKE This application is a continuation of application Ser. No. 484,878, filed Sept. 3, 1965 and now abandoned.

This invention is concerned with devices for attachment to portable rotary grinding tools using grinding discs, to remove the spoil, waste and dust particularly when the spoil and dust of such a size as to be harmful to human respiration, or prevents continuous operations of the tool.

Numerous proposals have been made for extracting dust and waste particles from permanently installed cutting, grinding and polishing tools in factories and workshops but when the grinding and cutting operations are to be carried out in different places by the same toll for example in civil engineering and building projects, dust prevention and disposal is a serious and ever present problem. ln certain circumstances the materials being ground away may form pyrophoric dust which introduces the danger of fire as well as the danger of lung damage.

Portable grinding tools are well known in civil engineering and related fields but when used to cut brick, concrete, stone and the like they produce enormous quantities of spoil and dust which spreads from the area surrounding the cut so quickly that the tool becomes invisible to the operative after a few seconds of cutting. This is pronounced when cutting inside a building.

The application of water to the cutting area is messy, troublesome, sometimes inconvenient and usually unsuccessful and often not suited to the type of grinding discs which are required for masonry.

The present invention is designed to overcome the limitations outlined above and proposes an arrangement whereby the use of grinding tools as described may be made more acceptable, particularly for indoor use.

According to this invention there is provided for use with a rotary tool of the type using one or more thin grinding or cutting members, an extraction device comprising a guard shaped to enclose part at least of the said member or mem bers, having an open end to engage with the surface to be worked and a spoil outlet located substantially tangentially to the emergent working edge of the member so as to collect spoil thrown from the wheel, and means to connect the device in an operative position relative to the tool.

Addition air may be supplied by means of vents located near the open edge of the guard.

The total area of the inlet or inlets is preferably at least as large as the area of the outlet, but smaller inlets work almost as well.

The outlet usually subtends between itself and the open edge, an angle of between 90 and 130 depending upon the depth of penetration intended or permitted by the guard.

The guard is preferably connected to the tool such that the selected outlet angle does not change as the wheel moves further into the surface to be cut.

The guard is preferably a one-piece housing the tool being provided with an extension arm and the guard being pivoted to the end of said arm at a point opposite to the location of the outlet.

The guard is normally urged by spring means into a position enclosing the major part of the cutting wheel, which latter may be swung into the surface to be cut thereby allowing a greater depth of out while maintaining the edge of the guard in contact with the surface to be cut so preventing the escape of spoil.

The purpose of providing a central aperture to the guard is to admit extraneous air into a zone of low-pressure air within the guard caused by the air being spun from the center by centrifugal force to the peripheral zone of the guard by the rotating disc, creating a zone of higher pressure air such that the air mixes with the spoil generated at the cutting edge of the wheel and carries it to the outlet. The uneven abrasive surface of the cutting disc is sufficient, if the speed of rotations fast enough,

to impart considerable momentum to the air within the guard and therefore, the necessarily airflow speed to remove the spoil is ensured. Usually the peripheral speeds required for cutting, that is in the region of 6,000 r.p.m. combined with the abrasive surface of a sintered wheel are sufficient to create adequate air movement to send all the spoil through the guard outlet.

We have found that the extraction may be enchanced in various ways. Firstly the outlet may be shaped such that a venturi is formed, that is by giving the outlet a conical shape. This has the effect of collecting both light and heavy particles thrown off the disc along diverging paths. The outlet is preferably smoothed interiorly so as to promote smooth airflow. SEcondly the space above the disc and below the disc is preferably kept shallow of the order of half an inch deep. The existence of only a shallow space above and below the disc ensures that only a small volume of air may be in the vicinity of the disc, and this enables the wheel to raise the speed of the airstream to such a degree that both light and heavy spoil particles spun off the surface of the cutting disc are forced from the outlet.

Thirdly the space or pocket within the guard nearest the entering edge of the disc suffers from a pileup of air at the surface to be cut and this space is preferably closed off by a short diagonally situated wall so that the interior contour of the guard more closely follows that of the disc when in the cutting position. This prevents the air being blown into the cut being made.

The spoil may be collected in a filter bag of loose weave connected to the guard outlet. The bag is selected to retain the spoil but must not set up too great a back pressure to the airflow emanating from the guard. In use the airflow set up by the disc alone is usually not great enough to inflate a filter bag.

The guard may however be in two or more parts with spring means expanding them to enclose the major part of the cutting wheel, the edge of one such part being adapted to engage the surface to be cut and to be telescoped into the other part or parts as the depth of the cut increases.

However, the efficiency of spoil extraction may also be improved by providing a zone of reduced pressure at the outlet.

The reduced pressure may be set up in two ways. Firstly by the provision of a fan driven by the cutting tool, and ducting and a nozzle through which the fan may discharge the air into the venturi part of the outlet so as to create a partial vacuum in the outlet zone. The nozzle preferably projects as little as possible into the outlet zone thereby causing least turbulence to the airflow. The extra airflow contributed by the fan is usually sufficient to inflate a filter bag easily and to overcome the back pressure of the filtering action. Secondly a zone of reduced pressure may be provided by a vacuum pump drawing the spoil and air through a filter pad. [n this instance the provision of an inlet in the guard is not necessary, although preferable, as the purpose of the pump is to create a partial vacuum inside the guard which is destroyed only by extraneous air entering the slot or kerf which is cut by the wheel.

The edge of the part of the guard which contacts the surface to be cut may be provided with an outwardly directed flange. The greater area afforded by the flange enables the tool to be moved more steadily over the surface, being less susceptible to diversion by upstanding mortar or surface blemishes than would be the case with a plain rim. The flange may also be extended and modified so that the plane of the flange lies at 45 to the plane of the surface to be cut and therefore, also the plane of the cutting wheel. The flange will be arranged to clear the wheel as the latter moves past it into the surface making one side of a V-cut. It is proposed to form the latter type of flange as a fitment to removably engage the permanent flange of the guard.

Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which:

HO. 1 shows a perspective view of apparatus for cutting continuous slots in mortar,

FIG. 2 shows a similar view of apparatus for cutting slots in two intersecting surfaces,

FIG. 3 shows a similar view of apparatus for cutting, grooving and chasing masonry, and

FIG. 4 shows a similar view of another embodiment for the same purpose, and

FIG. 5 is a vertical cross-sectional view of FIG. 1.

EQUIPMENT FOR CONTINUOUS CUTTING OF MORTAR Referring to FIGS. II and 5 the equipment for cutting mortar such as would be needed to insert a dampproof course in an existing building comprises a portable hand tool employing a thin flexible grinding disc 2, a guard 4 for the disc 2, a power unit (not shown) to drive the disc through a flexible power cable 6 and a power unit to drive a vacuum pump which is connected to the guard via a cyclone separator (not shown).

The portable tool consists of an angle grinding head 8, an inlet 10 for the flexible power drive cable 6 which acts as a handle for manipulations, and an outlet 10 for a drive shaft. The disc 2 is driven in a clockwise direction, see Arrow A, FIG. I, or anticlockwise movement of the disc in FIG. 5, relative to the drive side of the disc at 38006000 r.p.m. depending on the safe running speed of the disc, by a 2 b.h.p. electric motor now shown. A fiberglass and resin grinding wheel disc 2 14" in diameter and one-eighth inch thick made by FLEX- IVIT is clamped to the drive shaft.

The guard 4 encloses about one-half of the grinding disc and is substantially semicircular in shape having a straight open edge 12 and terminating at the side downstream of the emergent cutting edge of the wheel in a straight closed side edge 14 situated at a little more than 90 to the said open edge 12. The straight closed edge forms one side of a triangular outlet extension 16 to the guard. The open edge of the guard is one-half inch longer than the diameter of the disc and the opening itself is I flinch deep. There is a clearance between the curved parts 13 of the guard and the rim of the disc of about one-fourth inch but this clearance increases as the disc wears. The guard itself is formed from sheet steel pressings welded at the seams, and is clamped by a ring flange to the angle head 8.

FIG. 5 discloses the guard 4 with its open straight edge I2 beyond which about half of the grinding disc 2 projects and a spoil outlet including side edge 14 forming one'side of the spoil outlet extension 16 and the spoil outlet 22. A clearance 110 for the disc 2 with respect to the interior of the curved portion of guard 4 is provided. The guard 4 is clamped by a ring flange 20 to the angle head 8, FIG. 1. The outlet is actually spaced to one side of the denoted rotational axis R and defines the entrance to the outlet duct D which has one side edge 14 extending from the end of said straight edge 12 opening on one side of the axis and the spoil outlet duct D and defines a longitudinal axis making approximately the critical right angle with the line joining the rotational axis of the disc to the point of intersection of the longitudinal axis and said edge 12 as shown in FIG. 5 by the broken lines A B and the 90 relationship of these two lines. This 90 relationship has proven essential and critical with respect to the proper functioning of the device with respect to the removal of substantially all the spoil removal particularly when the device is used inside an enclosure.

The outlet 22 is connected by a flexible hose 24 to the inlet of a cyclone separator through which spoil-laden air is drawn by means of a vacuum pump at the rate 140 c.f.m. Such apparatus is supplied by the British Vacuum Company.

In use the vacuum apparatus is started up and the disc revolutions brought up to maximum by a clutch provided on the power unit. The guard is held by the cable drive inlet and the hose outlet with the outlet end of the straight open edge contacting the wall, the spinning disc being as yet spaced from the wall. The tool is then pivoted upon the point of wall contact until the disc enters the mortar of the wall. Even though the open edge of the guard is still spaced from the wall by a wedge-shaped gap the spoil which leaves the wheel at an angle slightly greater than passes down the outlet also lying at that angle.

Some air revolves within the guard but most of it is drawn off by the vacuum pump. Very little dust escapes during the initial entry of the disc and none escapes when the disc is fully in the wall.

The open edge of the guard is then moved along the mortar line abutting the wall all the time, thereby cutting a S'rinch deep slot in the mortar and the vacuum set up within the guard is partially destroyed by extraneous air drawn in through the slot already cut.

The outlet is arranged at 90 to the open edge of the guard because the spoil follows a path which is approximately tangential to the point on the rim of the wheel where the rim emerges from the mortar.

Although the disc is not insertable into the wall up to its diameter when the tangent would be at 90 to the wall, the spoil tends to move in the direction of the disc rotation and this corrected path is made the axis upon which the outlet is situated.

The equipment enables dust free cutting Sinch deep through most mortars at the rate of 1 foot per 10 seconds.

EQUIPMENT FOR CU'I'IING SLOTS IN THE MORTAR OF TWO WALLS INTERSECTING AT RIGHT ANGLES Referring next to FIG. 2, a special problem is presented when it is necessary to cut a slot at the intersection of a pair of walls because the enhanced thickness of the walls prevents penetration sufficient to cut entirely through the intersection.

For such work the guard for an angle head grinder disc is a flattened substantially quadrant-shaped casing 204 which encloses the grinding disc 202.

The V-shaped front part 212 is open along both edges the latter being protected by rubber strips, and is bisected along the upper surface of the guard by a slot 226 extending rearwardly to abut the center of the surface of the guard.

The slot 226 is wide enough to receive the shaft 228 of the angle head 208 and is bordered by two lengths of angle iron 230 welded to the said surface and extending in rearwardly diverging paths to the edge of the arcuate part 218 of the guard.

The ends of the two angle iron braces 230 overlap the upper face of the casing and have tapped holes in the overlapping parts 232. The lower face of the guard is braced by a flat bar 234 which is welded thereto so that the ends of the bar overlap the casing directly beneath the overlapping parts of the angle members. The bar has similar tapped holes and two levelling bolts 236 are carried in the two pairs of tapped holes. In this way the device may be slid over the floor keeping equidistant therefrom.

The rear part of the guard is shaped to form a smoothly contoured outlet nozzle 216 for connection to vacuum equipment as described in the previous example. The extreme end of the V-shape is cut away to form a blunt end 238 which if left sharp might prevent the open ends mating closely with the walls.

The angle grinder 208 and disc assembly is free to slide from a position within the casing to a position where the angle grinder is close up to the intersection of the walls, permitting the slot cut by the disc to meet other slots cut by the equipment previously described.

GUARD FOR CHASING TOOL EQUIPPED WITH l0 INCH DIAMETER DISC Chasing in this specification refers to the cutting of slots l'rinch deep in walls in pairs so that the margin of wall between the slots can be easily chipped out to form a recess for pipes or wires or the like.

Equipment comprises a portable PERLES HSW 56/6 power tool which has a 1200 -watt, 1.6 -h.p. electric motor. The motor turns a 10 inch flexible abrasive disc made of silicon carbide and resin (by RASTA, Switzerland) at 6,000 r.p.m. in

a clockwise direction throughan angle head attachment which is adapted to reverse the normal anticlockwise direction of the motor shaft.

Referring now to FIG. 3 that shaft of the angle head 308 projects through a protective sheet steel guard 304. The guard is of substantially semicircular shape terminating in a flat open edge 312, inch wide, which is surrounded by an outwardly turned flange 342 which mates with the surface to be cut. The guard forms a flattened casing 1%inch deep around the cutting disc 302 and the casing has along the side which is downstream of the emergent cutting edge of the disc a shaped outlet 316 l rinch in diameter, the midaxis of which lies at 125 to the flat open edge 312. The outer edge 314 of the outlet 316 is curved outwardly so as to cause the particles formed during cutting to flow without undue turbulance over the walls of the outlet. The edge 314 may be straight if desired but in practice it is found to cause a layer of packed spoil to accumulate on the edge. A curved edge is therefore preferred. The the drive side of the guard is provided with an elongated arcuate slot 346 llinch wide extending from the center of the guard to near the flat open edge.

The opposite side of the guard (not shown) is provided with a central aperture 2 inch in diameter which is coverable by a pivoting cover plate mounted on the guard.

The guard 304 is attached to the tool by means of a ring flange 320. The ring flange is part of an arm 348 which is of flattened triangular shape the apex 350 being provided with a hole which overlies corresponding holes in the top corner of the guard. A bolt 352 passes through the casing of the guard and through the arm 18 the assembly being clamped together by a pair of nuts and washers screwed on to both threaded ends of the bolt 352.

The area surrounding the bolt 352 is enclosed in a sealed compartment 354 which is packed with grease to ensure an easy pivoting action. The bolt 352 is shaped to prevent the casing collapsing when the nuts are tightened.

The triangular arm 350 has two arms which support the base part 356 which is deep enough to cover the slot 346 in the drive side of the guard. The corner of the base part nearer the said flat open edge 312 is provided with an aperture l liinch in diameter to receive the output shaft of the angle grinder head.

The ring flange 320 which connects the arm to the angle head 308 is surrounded by a circlip 358 so as to grip the periphery of the angle grinder. The circlip can be tightened by means of a screw in the usual way.

The base or cover part 356 of the bracket has a central projection 360 which engages the guideway defined by an arcuate strip of metal 362 bolted to the drive side of the guard. The arcuate metal strip has a slot therein such that a threaded pin projecting upwards from the drive side of the guard beneath the strip may move to and fro in the slot and may be locked in any desired position by a wing nut. The operator is able by clamping the wing nut to limit the travel of the disc in the arcuate slot and hence into the wall. In practice the discs wear quite rapidly and a quick-adjustment screw is provided to take up the wear.

Since the guard has a radius of 5 5/l6 inches over its semicircular part it is capable of pivoting rearwardly to enclose all the disc, uncovering at the same time the arcuate slot 346. The flange 342 surrounding the flat open edge may be placed up to the wall and when the disc is turning at full speed the power tool is gripped at the handle 362 and the outlet 322 and pivoted about the top comer bolt 352 against the pressure of spring means (not shown) which tends to resist the emergence of the disc. As the disc emerges it cuts the wall and at the same time the arcuate slot 346 is gradually covered up by the base part 356. The aperture on the opposite side may be then opened if desired.

In practice the necessary air ingress takes place through two sets of louvres (not shown) the first lying on the said opposite side of the guard located between the aperture 346 and the said flat open edge 312, the second laying between the aperture 346 and the top comer bolt 342.

TELESCOPING GUARD FOR CHASING TOOL EQUIPPED WITH 10 INCH DISC Referring now to FIG. 4 the guard comprises a main body portion 404 which is secured to the angle head 408 of the same power unit as used with the previous embodiment, by a V-shaped bracket 464. The wall of the main body portion has on outwardly curved wall on the outlet side. The open edge of the main body portion has an arcuate recess 446 in the upper surface of the said portion.

There is a triangular-shaped extension 466 adapted to telescope within the main body portion 404 and pivotally mounted thereto by a bolt 452 located at the outlet side of the main body portion. The extension 466 has an arcuate recess 468 in its upper face corresponding to the recess 446 in the main portion so that the two together form an arcuate slot of variable length in which the output shaft 440 of the angle head can move. The extension is biased into a fully extended position enclosing the disc 402 by spring means not shown. The extension has an open end and a flange 442 similar to the guard shown in FIG. 3.

In use the vacuum equipment and motor are switched on so that air passes down the outlet and when the disc is running at full speed within the guard the open end of the extension is placed against the wall to be worked and a tilting pressure applied to the main body portion, about the bolt. The extension then telescopes into the main body portion against spring pressure allowing the disc to enter the wall.

The purpose of both latter guards is to direct the spoil created at the cutting edge of the disc away from the said edge and toward a spoil collection area. 1 have tried to collect the spoil in a filter bag of woven material connected to the outlet but the rate of increase of weight due to accumulating spoil was of great that only short chases could be done before the bag grew too heavy to be comfortable, but for short chases the filter bag was quite acceptable.

Hence I prefer to use a flexible outlet pipe leading to a cyclone separator through which air is drawn by a vacuum pump at the rate of 40 cu. ft./min. I

In order to improve the shape of the chases an adjustable guide may be mounted on an arm extending from the guard such guide being insertable into and slidable in the first slot of the chase, thereby enabling the disc to cut the second slot parallel to the first.

In another embodiment not illustrated the guard is made slightly deeper and adapted to enclose two discs side by side so as to cut two parallel cuts simultaneously leaving masonry between to be chipped out at a speed with a power chisel. The increased torque for this embodiment is preferably supplied by flexible cable driven to the discs rather than by a hand tool which would tend to burn out if used continually under the extra load.

What I claim is:

l. A dust free method of removing mortar or the like from between rows of superimposed bricks or the like by the use of a guard having a planar open edge and a spinning cutting disc substantially enclosed and pivotally carried by said guard and operating through said open edge, and a vacuum discharge passageway in said guard extending outwardly from one end of said planar open edge at an angle greater than to the plane of said open edge comprising, turning on the vacuum apparatus, and the spinning cutting disc to maximum bringing the guard into substantial angular contact with the wall with the said one end of the planar open edge into initial substantial point contact with the wall, pivoting the guard about the point of wall contact until the disc enters the mortar of the wall, a predetermined depth and simultaneously bringing the open edge of the guard in full contact with the wall and then moving the guard and cutting disc while in full contact along the mortar line of the wall whereby the path of the spoils leaving the rim of the cutting disc is maintained substantially in line with the discharge passageway in the guard at all times including the initial cutting period.

2. The method of claim 1 wherein the outlet is shaped to form a venturi to thereby enchance the extraction force.

3. The method of claim 1, wherein a shallow space is formed between the disc and guard both above and below the disc to cut down the volume of air close to the disc.

4. The method of claim 1, wherein the axis of the outlet path for the spoil is at all times approximately tangential to the point on the rim of the cutting disc where the rim emerges from the mortar and the guard is swung relative to the cutting disc to maintain said path at all times substantially in line with the discharge passageway in the guard.

5. A dust free method of removing mortar or the like from between rows of superimposed bricks or the like at the intersection of a pair of walls by the use of a guard having two straight open edges forming a V-shaped opening at one side and a vacuum discharge passageway at the other side and enclosing a spinning cutting disc operating operating through the apex of said V-shaped opening comprising, turning on the vacuum apparatus, and the spinning cutting disc to maximum, bringing the guard into contact with each wall with the straight open edges of the V-shaped opening in contact with the respective walls, then pivoting the cutting disc through each of the open edges and simultaneously into contact with the mortar of each wall and cutting a slot in each wall and sucking off the spoil through the vacuum discharge passageway.

6. The method of claim 5, wherein the outlet is shaped to form a venturi to thereby enhance the extraction force.

7. The method of claim 5, wherein a shallow space is formed between the disc and guard wall on each side of the disc to cut down the volume of air close to the disc.

8. A dust free method of removing mortar or the like from between rows of superimposed bricks to a predetermined depth in a wall or the like by the use of a guard substantially enclosed pivoted spinning cutting disc operating through a planar open edge of the guard, said guard having a vacuum discharge passageway therein leading from one end of said planar open edge and at an obtuse and an acute angle thereto comprising, turning on the vacuum apparatus an the spinning cutting disc to maximum, bringing the guard against the wall with the planar open end at an arcuate angle to the face of the wall, contacting the cutter disc with the wall substantially aligning the path of the spoils leaving the rim of the cutter disc up with the discharge passageway in the guard and swing the planar open edge of the guard toward the face of the wall to maintain said substantial alignment as the disc cuts to the predetermined depth, then upon contact of the planar open edge with the face of the wall moving the guard and cutter along said wall.

9. The method as defined in claim 8, wherein said acute angle made by the planar open edge with the wall is substantially equal to the first-named acute angle made by the passageway with the planar open edge of the guard.

10. The method as defined in claim 8, wherein the fixed obtuse angle made by the passageway with the planar open edge is substantially the same as the angle made by the path of the spoils with the planar open edge when the disc is at its maximum depth in the wall.

11. A spoil guard for use with a cutting tool having a rotatable grinding or cutting disc, said guard comprising a housing for enclosing at least a part of the disc and defining a straight edged opening through which said disc can extend and a spoil outlet opening, means for mounting said disc in the housing and defining the rotational axis of the disc, said outlet opening being spaced to one side of said rotational axis and defining the entrance to an outlet duct, and the outlet duct having one wall extending from the end of said straight edged opening on said one side of the axis and the spoil outlet duct defining a longitudinal axis making approximately a right angle with the line joining the said rotational axis of the disc to the point of intersection of said longitudinal axis and said edge.

Claims

1. A dust free method of removing mortar or the like from between rows of superimposed bricks or the like by the use of a guard having a planar open edge and a spinning cutting disc substantially enclosed and pivotally carried by said guard and operating through said open edge, and a vacuum discharge passageway in said guard extending outwardly from one end of said planar open edge at an angle greater than 90* to the plane of said open edge comprising, turning on the vacuum apparatus, and the spinning cutting disc to maximum bringing the guard into substantial angular contact with the wall with the said one end of the planar open edge into initial substantial point contact with the wall, pivoting the guard about the point of wall contact until the disc enters the mortar of the wall, a predetermined depth and simultaneously bringing the open edge of the guard in full contact with the wall and then moving the guard and cutting disc while in full contact along the mortar line of the wall whereby the path of the spoils leaving the rim of the cutting disc is maintained substantially in line with the discharge passageway in the guard at all times including the initial cutting period.