US3347596A

US3347596A - Portable surfacing machine for terrazzo floors

Info

Publication number: US3347596A
Application number: US435958A
Authority: US
Inventors: Robert J Brejcha; Narciso G Modesto; Wayne F Ridenour
Original assignee: GENERAL STONE AND MATERIALS CORP
Current assignee: GENERAL STONE AND MATERIALS CORP
Priority date: 1965-03-01
Filing date: 1965-03-01
Publication date: 1967-10-17
Anticipated expiration: 1984-10-17

Description

C. 17, 1967 R L BREJCHA ET AL v3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March l, 1965 4 Sheets-Sheet 1 mw/W ATTORNEYS @Ct 17, 1967 R. J. BREJCHA ET AL 3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March l, 1965 4 Sheets-Sheet 2 N VEN TOR.

[gy-:2% l: l a Y ATTORNEYS @Cil 17, lg' R, 1 BREJCHA ET AL 3,347,596

PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Filed March v1, 1965 4 Sheets-Sheet ,5

C. 17, 1967 R BREJCHA ET AL 3,347,596.

PORTABLE SURFACING .MACHINE FOR TERRAZZO FLOORS Filed March i, 1965 4 sheets-sheetv 4 N RN . N pi mm? g ATTORNEYS*- 3,347,596 PORTABLE SURFACING MACHINE FOR TERRAZZO FLOORS Robert J. Brejcha, Westchester, Narciso G. Modesto, Morton Grove, and Wayne F. Ridenour, Chicago, Ill., assignors, by mesne assignments, to General Stone and Materials Corporation, Roanoke, Va., a corporation of Virginia Filed Mar. 1, 1965, Ser. No. 435,958v 7 Claims. (Cl. 299-10) The present invention relates to an improved method and apparatus for rough finishing cementitious cast surfaces, such as Portland cement, concrete, and the like, and has particular reference to the finishing or surfacing of terrazzo floors.

The art of terrazzo floor finishing has changed little in the hundreds of years which have elapsed since the art was developed. Basically, the procedure consists in casting a dispersion of marble chips in Portland cement along the supporting surface, trowelling the surface, and setting it by hydration of the cement. Then, the surface is abraded until the desired surface -nish is obtained. About the only concession to modern technology which has taken place in this art is the substitution of power driven abrasive blocks or rollers for the manually operated abrasive stone mounted on a long handle which had theretofore been employed.

The present commercial method of rough finishing terrazzo consists of rubbing blocks of a silicon carbide abrasive over the cast terrazzo surface under high unit pressure, in the presence of water which serves as a coolant and prevents filling or clogging of the blocks with the abraded product. The blocks are attached to rotating arms of a weighted portable machine which is maneuvered over the surface of the fioor in a random pattern by the machine operator. The terrazzo is gradually abraded from the surface, to a depth usually .measuring about 2 mils per pass, and forms a thick slurry when it combines with the Water covering the surface being finished. The condition of the surface is continually observed by the operator who must judge when a sufficient depth has been reached to expose the largest proportion of marble chips to cement binder. As a given portion of the door is finished, the operator moves to the next adjacent section and repeats theoperation While blending the -ground surfaces of the two sections.

Walls which have been previously finished are normally protected with a plastic film to prevent them from being splashed with the slurry. Nearby metal trim similarly must be protected from the slurry since it is quite corrosive in nature. Because of thelarge quantities of Water employed, the floors are normally completed in a newly erected structure before ceiling tiles are incorporated, to prevent moisture damage to the tiles.

Following the finishing operation, the floor is scraped in an attempt to remove .a portion of the slurry and also to move the major bulk of it to a location where it may dry out and from which it can be removed by shoveling. This clean up operation involves a substantial amount of time and labor and adds significantly rto the cost of the entire finishing operation.

Beside the disadvantages which are inherent in the process presently used due tothe necessity for using large volumes of water, the presently used commercial process is quite slow, since it is usually desirable to ,remove about 40 mils from the floor, and this takes an average of about 20 passes with presently available equipment. Furthermore, the operation as presently practiced can only be performed on a partially cu-red terrazzo floor which has been cured for less than'9 days. After that time, the abrading action becomes ineffective in removing surface mate- United States Patent O rial. This requirement demands careful scheduling of the entire terrazzo installation from pouring to finishing.

One of the largest machines presently commercially available for this operation includes 12 abrasive blocks which operate at about a 71/2 horsepower demand. This machine is able to rough finish terrazzo at a rate of approximately 500 square feet in an eight-hour day. This is accomplished with the use of two complete sets of abrasive blocks, a new set being installed for operation at the beginning of the working day and replaced at the middle Iof the day with a new set.

The present invention is directed to an entirely difierent concept in rough finishing of cementitious materials, particularly terrazzotloor surfaces. It does not rely upon abrading, but rather employs a cutting action resulting in the milling of the surface to a predetermined, controllable Idepth so that the fioor is cut in a single pass to the required depth. The process is entirely dry, rendering removal of fines more convenient without the clean up difiiculties which are encountered in conventional terrazzo finishing processes. What is more, the finishing of the floor is accomplished at substantially lower power requirements than presently employed commercial operations.

The heart of the cutting mechanism of the machine of the present invention consists of a pair of counter rotating wheels, each of which has a plurality of hard cutter elements spaced along the periphery thereof, the two wheels being driven from a common drive source, with their projecting cutter elements being at interdigitated relationship. The two cutter wheels thus cut overlapping paths or tracks to a predetermined depth, depending on the elevation of the wheels. The machine is propelled in the forward or cutting direction by means of a frame supported on a plurality of wheels, typically a set of three wheels, two of which are located on one side of the machine, and the third on the opposite side to provide a datum planeqforvthe cutting action. The third Wheel is made vertically adjustable with respect to the other two, to provide an adjustable three point suspension system for the machine. To initiate material removal, the cutter wheels are slowly lowered vertically into the surface of the material to the required cutting depth, and forward driving motion is imparted to the wheels. To this end, each of the wheels is preferably provided with its own drive motor. With the tool elements equally spaced on the Wheel peripheries, and with the rotational speed and horizontal travel held constant, each cutter element then removes an equal amount of material for each rotational pass.

The basic mechanism of material removal in accordance with the present invention is failure of the material by the process of shear due to loads imposed by the cutting element. When ductile metals are cut in this manner, a continuous chip is formed since the shear deformation occurs without fracture of the metal. In that case, the metal deforms by shear in a narrow zone extending from the tool cutting edge to the work surface. In the case of low ductility or brittle materials, such as in the case of cement and terrazzo mixtures, a discontinuous chip results. The discontinuous chip is formed because the material is not able to undergo the required amount of shear deformation without fracture, and therefore the fracture occurs intermittently along the shear plane, breaking the chip into small segments.

An object of the present invention is to provide an improved machine for surfacing terrazzo surfaces and the like without the use of an abrading type action.

Another object is to provide a completely dry finishing process of the type described.

Another object of the invention is to provide an improved portable terrazzo surfacing machine in which the. depth of cut can be precisely controlled, and succeeding cuts can be blended together to form a uniformly finished surface.

A further object is to provide a finishing method for terrazzowhich can be used after extended curing times.

Still another `object of the invention is to provide a machine for surfacing floors of the type described which is capable of substantially greater productivity than comparable machines used in the past, and does not involve extensive clean-up.

Another object ofthe invention is to provide a machine for surfacing cementitious floors and the like which operates at lower power requirements for the same amount of surface removal.

Still another object of the invention is to provide an improved cutter wheel design for the milling of cementitious surfaces and the like to provide a precise cut to a predetermined depth.

Still another object of the invention is to provide an improved cutting wheel assembly which provides a milling action rather than an abrading action on a terrazzo oor.

Another object of the invention is to provide an improved method for surfacing terrazzo surfaces and the like enabling succeeding cuts to be precisely matched.

A further description of the present invention will be made in conjunction with the attached sheets of drawings which illustrate a preferred embodiment thereof.

In the drawings:

FIGURE l is a bottom plan view of the machine, particularly illustrating the configuration of the cutting wheels;

FIGURE 2 is a side elevational view of the machine;

FIGURE 3 is another side elevational view of the machine;

FIGURE 4 is a top plan view of the machine;

FIGURE 5 is a view partly in elevation and partly in cross-section of the machine showing the drive elements more specifically;

FIGURE 6 is a fragmentary view in perspective of a single cutting` element, illustrating its orientation with respect to the remainder of the cutting wheel for proper cutting action;

FIGURE 7 is a fragmentary view in elevation illustrating the positionof the cutting elements `during the first cut provided by the machine;

FIGURE 8 is a view similar to FIGURE 7 but showing the position of the elements prior to the start of a succeeding cut; and

FIGURE 9 is a view similar to FIGURES 7 and 8 and showing the position of the elements during succeeding cuts.

As shown in the drawings:

In FIGURE l, reference numeral 10 indicates generallya main frame supported for forward movement in the cutting direction by means of a set of wheels consisting of substantially

coplanar wheels

11 and 12 secured to one side of the frame, and a `vertically positionable drive wheel 13 secured centrally of the opposite side of the main frame 10. Each of the

drive wheels

11, 12 and 13 has an associated drive motor, 14, `16 and 17 respectively, therthree motors being driven in synchronization. The

drive wheels

11, 12 and 13 are resiliently surfaced, being composed of a hard rubber `tire having a Durometer A reading of about 80 to 90. The tires are made resilient so that they can ride over slight surface irregularities without significantly changing the machine elevation.

A sub-frame 18 is carried by the main frame 10 in vertically adjustable relationship, and the sub-frame 18 carries a pair of4

cutter wheels

19 and 21 which provide the cutting action in a cutting plane. As best illustrated in FIGURE 1, the

cutter wheels

19 and 21. each carry a plurality of equally peripherally spaced cutting elements 22, the cutting elements 011` the wheel 19 being in inter' digitated relationship with the cutting elements on the wheel 21. The cutting elements 22 are preferably cotilposed of a hard material such as tungsten carbide. Specifically, we prefer to employ the commercially available material known as Carboloy 999 since it has excellent heat, abrasion, and wear resistance. This material is composed of about 97% tungsten carbide and 3% `c0- balt by weight. It is `formed by blending the powdered materials in proper proportions, compacting them under extremely high pressures lin a die, and sintering them into a solid piece. The final density of the product is about 15.25 grams per cubic centimeter, and `its hardness, as measured on the Rockwell A scale is 92.7.

The manner of securing the cutting elements 22 to the cutter wheels19 and 21 is preferably one which permits rapid release of the cutting elements for purposes of reorientation or replacement. We have found it particularly effective to use the tool geometry and type known commercially as Carb-O-Lock, marketed by the General Electric Company which permits rapid tool changeover by means of a quick action locking principle for rigidly retaining the carbide inserts, and an insert design which is shaped geometrically to offer a large` number of cutting edges so that a new cutting edge can be presented to the work by repositioning the cutter element 22 in its socket with a sharp cutting edge presented to the'work.

The orientation of the cutter element 22 with respect to the plane of the wheel in which it is located is best illustrated in FIGURE 6 of the drawings. In the particular embodiment there illustrated, the cutter element 22 taxes the form of Va generally square plate having rounded corners 23, typically with 'a radius of 1/16 inch. With this type of cutter element, the eight edges; provide cutting surfaces which can be presented to the work merely by embodiment there illustrated, the cutter element 22 taxes respect to its associated cutter wheel.

In FIGURE 6, the axis of the cutter wheel is indicated at reference numeral 24, and a reference radial plane extending from the centerline of the cuttingwheel is represented by reference numeral 26. In order to achieve the proper type of cutting action, the cutting element 22 is positioned so that it has a negative radial rake with respect to the radial plane 26, the rake in this direction being defined by the `angle a. The cutter element 22 should also have a negative axial rake, represented by the angle b. The corner angle, represented by reference c is not particularly critical, but should be less than for a square shaped insert, otherwise the adjacent or bottom side of the insert would drag over the finished surface and a propercut would not be made. In practice, it was found that negative rake angles a and b should be on the order of 5, while75 vis appropriate for the corner angle c.

Referring to FIGURE 5, it will be seen that the

cutter wheels

19 and 21 are fitted to shafts 27 and 28, respectively, by means of tapered mating diameters indicatedy at 29 and 31 respectively, The

wheels

19 and 21 are retained on the shafts by means of locking bolts 32. The

cutter wheels

19 and 21 are of sufcient mass to act as flywheels to drive smoothly through` load uctuations without creating excessive vibrations.

The ends of the shafts 27 and 28 are mounted between bearings 34 and 35, and bearings'36 and 40 respectively. To the `center of each shaft there is mounted a worm gear 37 and 38 respectively. The worm gearsy 37 and 38 are driven by a central worm 39 which, in turn, is driven from a belt 41 trained about a pulley 42 connected to the drive shaft of a cutter drive motor 43 carried by the subframe 18. The two cutter wheels 19 `and 21 are thereby drivenat identical speeds in opposite directions.

The cutter wheels, the worm gear drive, and the motor assembly are connected to the main frame '10 by means of

jack screws

46, 47, 48 and 49 received in suitable bearings (not shown) in the main frame 10. Each of the jack screws 46 through 49 inclusive is rotated by means of associated

sprockets

51, 52, 53 and 54 respectively. About the sprockets there is trained a chain 56 which is driven from a drive sprocket 57 connected to a drive shaft S8 of a drive motor 59 (see FIGURE 5). An idler sprocket 61 is provided to adjust the tension on the chain 56. The drive system is such as to position the sub-frame 18 in one of the two positions with respect to the main frame 10, namely, a retracted position in which the cutter elements 22 are elevated slightly with respect to the plane or suspension provided by the drive wheels (see FIGURE 8), or in a cutting position in which the

cutter wheels

19 and 21 are set to the predetermined cutting depth required for each pass of the machine (see FIGURE 7).

The drive wheel 13 is driven by means of a bevel gear 63 secured to a drive shaft 65 as best illustrated in FIGURE 5 of the drawings. The wheel 13 rotates about a shaft 64 and has a bevel gear portion 70 engaging the bevel gear 63. The shaft 64 has a vertical portion 66 provided with a rack 67 engageable by a gear 68. The latter is driven by a motor 69 to position the wheel 13 at the proper elevation so that it provides a substantially horizontal datum cutting plane for the cutter wheels when the

wheels

11, 12 and 13 are in the cutting position.

The nes produced by the milling operation are drawn into the hollow centers of the shafts 27 and 28 respectively by providing passages 71 and 72 respectively in the

cutter wheels

19 and 21. The hollow shafts are in communication with a pair of

liexible ducts

73 and 74 which vare connected to the inlet side of a blower 76 operated from the main drive motor 43. The blower discharges into a conduit 77 which delivers the fines to a collector 78 which may consist of a conventional bag type lter mounted over the top of the main framework. In order to increase the velocity of the air which flows past the cutter elements 22, it is desirable to put a shroud or skirt 79 surrounding the base of the main frame, as best illusstrated in FIGURE 2 of the drawings. The air movement within the shroud is of suicient velocity to carry the residual lines or chips into the air stream and up to the lter elements in the collector 78.

The controls for the unit are located in a control box 81 connected to the machine by means of a flexible cable 82. Also coming into the machine is a liexible power cable 83 as illustrated in FIGURE 5. The main power cable and the'control cables from the unit are taken oli at one side to enable the operator to conveniently control the cable-and keep it from the path of the cutters. All controls are handled by a single control box 81 without a rigid connection to the nishing machine.

At the completion of one cutting pass, the machine must be moved laterally in order to position it for the cutting of the next track adjacent to and merging with the track previously cut. For this purpose, there is provided two additional pairs of wheels identified at

reference numerals

84, 85, 86 and 87 in the drawings. These wheels are rotatably mounted on shafts which are received within housings designated at

reference numerals

88, 89, 90 and 91 respectively. Means (not shown) are provided within the housings 88 through 91, inclusive, to raise and lower the wheels, and to drive them in the lateral direction. In their retracted position, as illustrated in FIGURES 2 and 3 of the drawings, the wheels 84 to 87 are raised from contact with the oor line, so that the weight of the machine rests on the three

drive wheels

11, 12 and 13. With the wheels in their extended position, however, the weight of the machine rests on the wheels 84 to 87, and the drive wheels 11 to 13 inclusive are raised above the level of the floor so that the machine can be moved laterally to the next adjacent cutting path.

The sequence of operations involved in surfacing a floor is lbest illustrated in the showings of FIGURES 7 to 9 inclusive. In position for the starting cut, the

cutter wheels

19 and 21 are fully retracted into their completely retracted position, so that they are clear of the floor generally indicated at F. The adjustable drive wheel 13 is also in its uppermost position relative to the main frame and the weight of the unit rests on the three drive 6

wheels

11, 12 and 13. The contact areas of these three drive wheel tires then all lie in a single datum plane which is parallel to the cutter faces.

With the three drive wheels at rest, the cutter wheels 19 and 21 'are rotates at standard cutter speeds. The filter system contained in the collector 78 starts operating with the

cutter wheels

19 and 21. The vertical cutter actuators driven by the chain r56 are energized, and the cutters lower gradually to lower the cutting plane to a predetermined depth, usually on the order of 40 mils below the surface F, as illustrated in FIGURE 7 of the drawings. When the cutters reach this position, the forward feed motion begins by the operation of the three

Vsynchronized drive motors

14, 16 and 17. The forward motion continues until the operator manually stops the action, at which time, the

cutter wheels

19 and 21 may be manually or automatically retracted to the full clearance position.

Assuming that the following machining pass will be made parallel and adjacent to the first pass, the operator then lowers the

lateral drive wheels

84, 85, 86 and 87 until the unit is raised from the floor, and all of the weight of the unit rests on these four wheels. The unit is then moved laterally along on these wheels until it reaches a position comparable to that shown in FIGURE 8 wherein the two

drive wheels

11 and 12 will (when lowered) come to rest on the uncut surface, while the vertically adjustable wheel 13 will come to rest in' the track 93 cut by the previous pass. Then, the actuator for the vertical adjustment of the drive wheel 13 is energized, namely, the motor 69 which drives the gear'68 to lower the wheel 13a distance equal to the depth of the previous cut. When the unit is then finally lowered s0 that the entire weight is again on the three drive wheels, the cutting plane of the cutter wheels will again be near horizontal. When the cutter wheels are again actuated vertically downwardly to cut to the same depth as the previous track, as illustrated in FIGURE 9, the new cut will blend with the previous cut. With the lowering of the

cutters

19 and 21, the cycle is once again repeated, except that for all additional passes, the single drive wheel 13 need not be vertically adjusted since all succeedng cuts will be repetitions of the second c`ut described in conjunction with FIGURES 8 and 9.

Cutter yspeed should be correlated with feed rate to secure an adequate speed while still maintaining a reasonabletool life. Our tests lhave shown that when a Carboloy 999 cutter point was operated at a speed of approximately 272 feet per minute (linear speed of the cutting element) and a feed rate of 0.0115 inch per tooth was used, it produced a surface condition which could be easily polished out, and that the tool life under these conditions was about 4 hours, an acceptable gure. Tests indicated that the power to produce such a cut was below 0.1 horsepower per cubic inch per minute of material removed. It was also determined that the curing time or aging of the terrazzo from periods varying from 4 days to 30 days had little or no effect upon the tool life or the other cutting parameters.

At the above operating conditions, using two cutter wheels each of one foot in diameter and having l2 carbide cutting elements, the cutter wheels would be operated at approximately 87 r.p.m., and at a forward feed rate of about 12.0 inches per minute. This results in a surface removal rate of about 2 square feet per minute, and a volume removal rate of about 11.5 cubic inches per minute, assuming the depth of cut to be 0.040y inch. At this rate, the surface area finished in 8 hour of operation is about 960 square feet. It is estimated that the above operation requires less than 1.2 horsepower, a figure considerably less than that employed in the abrading type machines presently in use.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

1. A machine for surfacing terrazzo surfaces and the like comprising a main frame, a pair of drive wheels at one end of said frame, a third drive wheel mounted on the opposite end of said frame, each of said wheels having resilient surfaces thereon, means for changing the elevation of said third wheel with respect to said pair of drive wheels, means for driving the three drive wheels, a subframe carried by said main frame, a pair of cutter wheels mounted on said sub-frame, means for varying the elevation of said sub-frame relatively to said main frame, a plurality of additional wheels carried by said main frame, means for raising and lowering said additional wheels lto engage the surface being worked and ,thereby raise said three drive wheels `oi said surface to permit lateral movement of said machine on said additional wheels and permit retraction of said additional wheels so that said surface is engaged py the three driven wheels;

2. A machine for surfacing terrazzo surfaces and t-he like comprising a main frame, a plurality of resilient drive wheels on said main frame for propelling said frame in a forward direction, `means for adjusting the elevation of one of said drive wheels with respect to the others, a plurality of retractible wheels for propelling said main frame in a lateral direction, a sub-frame carried by said main frame, means for positioning said sub-frame vertically with respect to said main frame, a pair of cutter wheels carried by said sub-frame and rotatable along parallel vertical axes, each of said cutter wheels having a plurality of cutter elements peripherally spaced thereon, with the cutter elements of one wheel being in interdigitated relation with respect to the cutter elements of the other, and a common drive meansy for said cutter wheels mounted on said subframe.

3. The machine of claim 2 which includes a separate drive. motor for each of said drive wheels.

4. The method of surfacing a terrazzo iioor or the like which comprises supporting a cutting mechanism on three wheels which ldeiinea horizontal datum cutting plane, said cutting mechanism including a pair of counter rotating wheels each having peripherally spaced cutting elements thereon oriented such that each element provides a -point cut along the surface, lowering said wheels while rotating the same to cut said floor `to a predetermined depth, moving the wheels forwardly to thereby cut a track of said predetermined depth, raising the cutter wheels out of cutting engagement with said oor, moving said cutting mechanism laterally so that at least one of said wheels rests on an uncut surface while the remaining wheels rest on the previously cut track, lowering said remaining wheels by the amount of said predetermined depth of cut, and lowering said cutting wheels and moving said machine yforwardly to cut a track parallel to the first track and having substantially the same depth of cut. 5. A machine for surfacing terrazzo surfaces and the like comprising: a main frame, drive means on said main frame including at least three drive wheels at least one of which is selectively vertically adjustable with respect to said main frame for maintaining alignment of said main frameina datum plane, a sub-frame carried by said main frame,

a pair of cutter wheels mounted on said sub-frameV for counter-rotation on spaced parallel axes, cutter elements on said cutter wheels arranged for interdigitated overlapping cutting action in a cutting plane, and means for selectively vertically adjusting said sub-frame with respect to said main frame to vary the elevation of the cutting plane with respect to the datum plane.` 6. The machine as defined in claim 5 wherein said drive wheels are comprised of resilient material.

7. The machine as defined in claim 5, each of said cutter elements comprising a radially extending .plate having a plurality of rounded cutting corners and being j positioned on its respective cutter wheel so as to have a negative radial rake and a negative axial rake with respect to a reference radial plane extending from the` centerline of its cutter wheel.

References Cited UNITED STATES yPATENTS 308,366 l1/1884 Maloy 125--5 1,647,066 10/ 1927 Westman ,299-25 XRv 1,812,771 6/1931 Blood et al. 299-41 2,584,738 2/1952 Reitz 299-39 X 2,769,626 11/1956 Becker 299-41 2,923,107 2/'1960 Biasoni 51-1177 3,102,372 9/1963 Vezner 51-177 ERNEST R. PURSER, Primary Examiner.

Claims

4. THE METHOD OF SURFACING A TERRAZZO FLOOR OR THE LIKE WHICH COMPRISES SUPPORTING A CUTTING MECHANISM ON THREE WHEELS WHICH DEFINE A HORIZONTAL DATUM CUTTING PLANE, SAID CUTTING MECHANISM INCLUDING A PAIR OF COUNTER ROTATING WHEELS EACH HAVING PERIPHERALLY SPACED CUTTING ELEMENTS THEREON ORIENTED SUCH THAT EACH ELEMENT PROVIDES A POINT CUT ALONG THE SURFACE, LOWERING SAID WHEELS WHILE ROTATING THE SAME TO CUT SAID FLOOR TO A PREDETERMINED DEPTH, MOVING THE WHEELS FORWARDLY TO THEREBY CUT A TRACK OF SAID PREDETERMINED DEPTH, RAISING THE CUTTER WHEELS OUT OF CUTTING ENGAGEMENT WITH SAID FLOOR, MOVING SAID CUTTING MECHANISM LATERALLY SO THAT AT LEAST ONE OF SAID WHEELS RESTS ON AN UNCUT SURFACE WHILE THE REMAINING WHEELS REST ON THE PREVIOUSLY CUT TRACK, LOWERING SAID REMAINING WHEELS BY THE AMOUNT OF SAID PREDETERMINED DEPTH OF CUT, AND LOWERING SAID CUTTING WHEELS AND MOVING SAID MACHINE FORWARDLY TO CUT A TRACK PARALLEL TO THE FIRST TRACK AND HAVING SUBSTANTIALLY THE SAME DEPTH OF CUT.