Abstract:
The invention proposes a solution for cutting a sheet of gypsum board quickly and allowing a flat cut edge to be obtained. The invention relates to a carriage comprising a chassis ( 101 ) fitted with: —means ( 102 ) for collaborating in a sliding manner with a cutting guide ( 200 ); —a handle ( 110 ) that can rotate with respect of the chassis ( 101 ) and comprises a means ( 111 ) for grasping, a retractable engagement claw ( 113 ) and a housing ( 112 ) to hold a blade ( 300 ); —a section piece ( 120 ) provided with at least three notches (A, B, C) in which to lock the rotation of the handle through reversible engagement of the claw, the notches being arranged such that: •the first notch (A) allows the blade to be retracted so that it is not in contact with the sheet; •the second notch (B) allows the blade to be arranged at an angle α to the sheet of gypsum board, in firm enough contact with the sheet to score it in order to form a cutting edge; •the third notch (C) allows the blade to be arranged at an angle β to the sheet of gypsum board in firm enough contact with the sheet to trim the cutting edge.

Description:
FIELD OF THE INVENTION 
     The invention relates to a carriage for cutting a sheet of plasterboard, to a cutting kit and to a method for implementing the kit. 
     BACKGROUND OF THE INVENTION 
     A sheet of plasterboard is a sheet made of a layer of plaster covered, on at least one face, by a sheet of cardboard or of paper. Generally, the two faces of the sheet are covered by a sheet of cardboard or of paper. 
     The sheets of plasterboard are generally manufactured in a factory, and are used to make partitions, ceilings, to line rough walls, etc. These sheets therefore replace the use of powder plaster dissolved in water in order to coat walls, which is a tiring and lengthy operation and which requires significant know-how to obtain an optimum composition of the plaster and a satisfactory flatness of the coated surface. 
     These sheets have the advantage of being easy to manipulate and of allowing for rapid work. Furthermore, less know-how is needed to position them compared to traditional plaster. Finally, the factory production makes it possible to obtain plasters of optimal composition. However, for cost and management issues, the factory production entails producing sheets of standard sizes. 
     Although there are different standard dimensions, in length and in width and in thickness, it is often necessary to cut these sheets to adapt them to the widths and lengths of the walls or of the ceiling of the room in which they are to be installed. 
     This cutting, done on the work site to the ideal dimensions, has to be rapid and as clean as possible to allow for two sheets to be easily positioned contiguously. 
     Then, a finishing has to be carried out by filling the interstice between two contiguous sheets of plaster, using a filler product such as plaster or ready-to-use coating. Once applied, this filling product is smoothed using the coating knife. 
     The finishing step has to be as rapid as possible. For this, the number of gestures required of the user has to be limited. A clean cutting of the sheets would make it possible not only to limit the quantity of filler product used, but also the number of gestures to be made to smooth the surface on and in the vicinity of the interstice. 
     There are a number of solutions for cutting a sheet of plasterboard. 
     The most widely used consists in “marking” the sheet with a cutter blade (a cutter blade, known from the prior art and illustrated in  FIG. 13 , consists of a plate having a doubly beveled edge, that is to say that both faces of the plate are beveled). 
     This operation makes it possible to cut the first sheet of cardboard and score the layer of plaster. Then, the operator exerts a stress on the sheet so that the layer of plaster is broken into two parts along the score. Finally, the operator cuts the second sheet of cardboard with his cutter to free the two sheet parts. Generally, in this last step, the second sheet of paper is torn rather than cut, which creates an irregularity on the surface of the sheet of plasterboard that has to be filled in the finishing stage. 
     This solution is dangerous for the operator because of the use of the cutter. In practice, the scoring obtained is never rectilinear, even with the use of a guide, and it often happens that the speed of the scoring movement results in a sudden deviation of the blade of the cutter from the guide to the body of the user. 
     It is for this reason that some companies prohibit their workers from using this practice. Some public institutions even prohibit this practice in their calls for bids, but in practice it is the method most widely used. 
     Moreover, this solution also has two technical drawbacks. Firstly, the use of a blade of the cutter generates non-rectilinear scores so that the break along the surface of the sheet can take forms that are so irregular that a new sheet has to be used and cut. Secondly, the cutting edge, obtained after having broken the layer of plaster, is still very uneven, in that the cutting edge obtained has numerous protuberances, even with a user with long experience. It is then difficult to fit two contiguous sheets whose cutting edge is uneven. It is also necessary, during the finishing stages, to use a significant quantity of filler material to obtain a perfectly planar surface between the two consecutive sheets. 
     To overcome this problem, some operators have proposed a second cutting solution consisting in using a straight-back hand saw or a pad saw. The teeth of the blade of this saw has to be chosen with care to avoid plaster chips and generating an uneven cutting edge. For the same reason, the cutting speed and frequency must also be suitable, which requires significant know-how. 
     When well done, this second cutting solution makes it possible to obtain a clean cutting edge. Nevertheless, this solution takes longer than manual cutting using the cutter. Furthermore, the plasterboard sheets of small thickness (less than or equal to 18 millimeters) are unsuited to the use of a saw. This solution becomes advantageous only for thicknesses greater than 20 millimeters because, beyond this thickness, the strain to be exerted to break the layer of plaster is too great and the break does not necessarily follow the score. 
     The aim of the present invention is therefore to propose a rapid and clean solution for cutting a plasterboard sheet. 
     SUMMARY OF THE INVENTION 
     For this, the invention proposes using a carriage supporting a cutting blade making it possible, on the one hand, to firmly secure the blade during the scoring so that the break along the surface of the sheet is rectilinear and, on the other hand, to perform a step of trimming the edge of the sheet after having broken the layer of plaster. 
     To this end, the subject of the invention is a carriage for cutting a sheet of plasterboard, the carriage comprising a chassis provided with:
         means for cooperating in a sliding manner, in use, with a cutting guide;   a handle, mounted to rotate relative to the chassis, and comprising a gripping means, a recess for a cutting blade and a retractable engaging claw;   a section piece provided with at least three notches for blocking the rotation of the handle in three angular positions by a reversible engagement of the retractable claw, the notches being arranged on the section piece such that, in use:
           the first notch allows the blade to be retracted away from contact with the sheet of plasterboard;   the second notch allows the blade to be arranged at an angle α with the sheet of plasterboard, with sufficient contact with the sheet of plasterboard to score it in order to form a cutting edge;   the third notch allows the blade to be arranged at an angle β with the sheet of plasterboard, with sufficient contact with the sheet of plasterboard to trim the cutting edge.   
               

     According to other embodiments:
         the retractable engaging claw can be linked to a tension spring pressing, in the rest position, the claw into a notch;   the carriage may also comprise a blade protection housing, when the claw is engaged in the first notch;   the third notch can be spaced apart from the second notch to allow for the trimming of a cutting edge of a sheet of plasterboard of a first thickness;   the carriage may comprise at least one additional notch at a distance from the third notch to enable the trimming of a cutting edge of a sheet of plasterboard of at least one second thickness;   the recess may contain a cutting blade comprising at least one scoring corner having a planar face and a beveled face, extended by at least one trimming edge having a planar face and a beveled face that are identical to those of the scoring corner;   the blade may also comprise at least one cutting notch arranged between the scoring corner and the trimming edge;   the beveled face of the blade may form an angle with the planar face of between 15° and 25°, preferably 20°;   the trimming edge may have a length greater than the thickness of the sheet of plasterboard;   the cutting notch may be curved; and/or   the blade may consist of a rectangular removable plate having two faces and comprising:
           four scoring corners;   four cutting notches;   four trimming edges,
 
two diametrically opposite scoring corners being symmetrical relative to the center of the rectangular plate, two consecutive scoring corners having a planar face and a beveled face that are opposite.
   
               

     The invention also relates to a kit for cutting a sheet of plasterboard, comprising:
         a carriage according to the invention;   a cutting blade comprising at least one scoring corner having a planar face and a beveled face, extended by at least one trimming edge having a planar face and a beveled face that are identical to those of the corner;   a cutting guide having two longitudinal edges and two ends, and comprising at least one rail suitable for cooperating in a sliding manner, in use, with the carriage provided with the cutting blade in order, in use, to guide the cutting blade in a manner parallel to the guide, and comprising, at least at one end of the rail, an abutment mounted to rotate and of profile section to secure, in use, the sheet of plasterboard.       

     According to other embodiments:
         the cutting kit may comprise:
           a carriage bearing a cutting blade comprising at least one scoring corner having a planar face and a beveled face, extended by at least one trimming edge having a planar face and a beveled edge that are identical to those of the corner;   a cutting guide having two longitudinal edges and two ends, and comprising at least one rail suitable for cooperating in a sliding manner, in use, with the carriage provided with the cutting blade in order, in use, to guide the cutting blade in a manner parallel to the guide, and comprising, at least at one end of the rail, an abutment mounted to rotate and of profiled section to secure, in use, the sheet of plasterboard;   
           the rail and the abutment may be provided with means for securing the abutment on the sheet of plasterboard;   the securing means may be spikes intended to be driven into the sheet of plasterboard;   the guide may also comprise, at at least one of its ends, a retractable stop means to allow, in use, for the coupling and decoupling of the rail with respect to the carriage;   the guide may comprise, at at least one of its ends, a means for damping, in use, the sliding at the end of travel of the carriage; and/or   the abutment may comprise two parts linked to one another by an articulation, the two articulated parts being provided with means for securing the sheet of plasterboard, the articulation comprising an end-of-rotation abutment allowing a relative rotation of the articulated parts up to 45 degrees, preferably up to 30 degrees.       

     The invention also relates to a method for implementing a kit according to the invention, for cutting a sheet of plasterboard, comprising the following steps: 
     a) providing a sheet of plasterboard comprising a layer of plaster and at least one sheet of cardboard or of paper; 
     b) having the carriage cooperate in a sliding manner with the cutting guide; 
     c) arranging the cutting guide between two edges of the sheet in a determined cutting direction, and placing the carriage at a first edge of the sheet; 
     d) actuating the retractable engaging claw to withdraw it from the notch in which it is engaged and pivoting the handle until the claw can be engaged in the second notch, so that the scoring corner of the blade is applied to the sheet; 
     e) displacing the carriage using the gripping means to score the layer of plaster along the determined cut, from the first edge of the sheet to the second edge of the sheet; 
     f) bending the sheet along the score obtained in the preceding step to break the layer of plaster along the score and obtain a cutting edge; 
     g) displacing the carriage using the gripping means to the first edge of the sheet; 
     h) actuating the retractable engaging claw to withdraw it from the second notch and pivot the handle until the claw can be engaged in the third notch, so that the trimming edge is applied against the cutting edge obtained in the step f); 
     i) displacing the carriage using the gripping means to trim the cutting edge, from the first edge of the sheet to the second edge of the sheet, 
     the step e) and/or the step i) comprising a cutting of said at least one sheet of cardboard or of paper of the sheet of plasterboard. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Other features of the invention will emerge from the following detailed description, given with reference to the appended figures which represent, respectively: 
         FIGS. 1 to 3 , left side perspective schematic views of a first embodiment of a carriage according to the invention in three different cutting positions; 
         FIGS. 4 to 6 , right side perspective schematic views of the first embodiment of a carriage according to the invention respectively in the three cutting positions of  FIGS. 1 ,  2  and  3 ; 
         FIGS. 7 to 10 , perspective schematic views of an implementation of the cutting method according to the invention; 
         FIG. 11 , a partial enlargement in perspective of  FIG. 23  illustrating the surface condition obtained after trimming of the edge of the sheet of plasterboard; 
         FIG. 12 , a left side perspective schematic view of a second embodiment of a carriage according to the invention; 
         FIG. 13 , a cross-sectional schematic view of a cutter blade illustrating the state of the art; 
         FIG. 14 , a plan schematic view of a first embodiment of a blade according to the invention; 
         FIG. 14   a , a plan schematic view of a variant of the blade of  FIG. 14 ; 
         FIG. 15 , a cross-sectional schematic view along the line XV-XV of the blade of  FIG. 14 ; 
         FIGS. 16 and 17 , plan schematic views of two embodiments of a blade according to the invention; 
         FIG. 18 , a perspective partial schematic view of the blade of  FIG. 17 ; 
         FIGS. 19 to 21 , plan schematic views of three other embodiments of a blade according to the invention; 
         FIG. 22 , a perspective partial schematic view seen from above, relative to the position of use, of a cutting guide according to the invention; 
         FIG. 23 , a perspective schematic view seen from above, relative to the position of use, of a cutting guide according to the invention; 
         FIG. 24 , a perspective partial enlargement of  FIG. 23  showing a first embodiment of means for securing the guide according to the invention on the sheet of plasterboard; 
         FIG. 25 , a perspective schematic view of a second embodiment of means for securing the guide according to the invention on the sheet of plasterboard; 
         FIGS. 26 to 28 , perspective schematic views of three embodiments of one end of a cutting guide according to the invention; and 
         FIG. 29 , a plan schematic view of a step of implementing a cutting guide according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a first embodiment of a carriage for cutting a sheet of plasterboard according to the invention. The carriage  100  comprises a chassis  101  provided with means for cooperating in a sliding manner with a cutting guide  200 . The cooperation means are, in this embodiment, small wheels  102  provided with a groove  102   a  intended to receive a part  201   a  of a rail  201  borne by the guide  200 . Such a guide will be described in more detail in relation to  FIG. 22 . 
     The small wheels  102  make it possible to slide the chassis  101  along the rail  201 . 
     The chassis  101  comprises a handle  110  mounted to rotate relative to the chassis  101 . The handle comprises a gripping means  111  consisting, in this exemplary embodiment, of a profiled hand-hold. 
     The handle also comprises a recess  112  (see  FIGS. 2 and 3 ) for a cutting blade  300 . 
     The chassis  101  also comprises a section piece  120  provided with three notches A, B and C. These notches are intended to block the rotation of the handle  110  by virtue of the engagement of a retractable claw  113  borne by the handle. Advantageously, the retractable engaging claw  113  is linked to a tension spring  114  pressing the claw toward the bottom of the notches. Preferably, the claw  113  can be actuated by a trigger  115 . 
     In this way, the user who holds the handle  110  by the hand-hold  111  can retract the claw  113  from the notch in which it is engaged (here the notch A) by pulling, with a finger of the hand placed on the hand-hold  111 , the trigger  115 , against the tension spring  114 . He can then pivot the handle  110  relative to the chassis  101  until the claw  113  is engaged in another notch B (see  FIG. 2 ) or C (see  FIG. 3 ). 
     By virtue of the section piece  120  and the notches A, B and C, the handle can be positioned in a preset manner in three angular positions by reversible engaging of the retractable claw  113  in the notches. 
     These notches are arranged on the section piece, such that, in use:
         the first notch A allows the blade  112  to be positioned out of contact with the sheet of plasterboard (see  FIGS. 1 and 4 );   the second notch B allows the blade to be arranged at an angle α with a sheet of plasterboard, with sufficient contact with this sheet to score it in order to form a cutting edge (see  FIGS. 2 ,  5  and  7 );   the third notch C allows the blade  300  to be arranged at an angle β with the sheet of plasterboard, with sufficient contact with this sheet to trim the cutting edge (see  FIGS. 3 ,  6 ,  10  and  11 ).       

     Preferably, the carriage  100  also comprises a protective housing  130  for the blade  300 , when the claw  113  is engaged in the first notch A. In this position, the blade is not in contact with the sheet of plasterboard. This position advantageously constitutes a secure transport position in which the blade is inaccessible to the user who cannot therefore be injured with the blade. 
       FIGS. 4 to 6  illustrate the cutting carriage illustrated in  FIGS. 1 to 3 , but seen from the opposite side relative to the section piece  120 . 
     In  FIG. 4 , the handle  110  is in the transport position illustrated in  FIG. 1 . The blade  300  borne by the handle is protected by the housing  130  and is not therefore visible in  FIG. 4 . 
     In  FIG. 5 , the handle  110  is in the position illustrated in  FIG. 2 , that is to say that the claw  113  is engaged in the notch B (not visible in  FIG. 5 ). In this position, the blade  300  borne by the handle  110  forms an angle α with the sheet of plasterboard  500 . The blade is in sufficient contact with the sheet  500  to score it in order to form a cutting edge. This step will be described in more detail in relation to  FIG. 7 . 
     In  FIG. 6 , the handle  110  is in the same position as that which is illustrated in  FIG. 3 , that is to say that the claw  113  is engaged in the notch C. In this position, the blade  300  borne by the handle  110  forms an angle β with the sheet of plasterboard  500 . In this way, the blade is in sufficient contact with the sheet of plasterboard  500  to trim the cutting edge and, advantageously, to cut the sheet of paper or of cardboard borne by the bottom face of the sheet (the bottom face being the face opposite to that which bears the guide  200  and/or the carriage  100 . 
     By virtue of the section piece  120  provided with notches, the angular positions of the handle are predetermined and preset. Thus, the user does not need to pay attention to the angle of the blade relative to the sheet of plasterboard. All he needs to do is to switch from one notch to the other to obtain the different positions of the blade. His only concern is to move the blade relative to the sheet. 
       FIGS. 7 to 11  illustrate the operation of the carriage according to the invention described previously. 
     On a sheet of plasterboard  500 , a cutting guide  200  is positioned along the cutting direction desired by the user. Before or after this positioning, the user makes the carriage  100  cooperate in a sliding manner with the cutting guide  200 . 
     Once the guide is positioned, the user places the carriage at a first edge  500   a  of the sheet  500 . In  FIG. 7 , the first edge is situated on the left; this arrangement is suitable for a use by a right-handed user. This first edge is the one which is located, on the side of the blade of the carriage and opposite the hand-hold of the gripping hand-hold. Then, the user actuates the retractable engaging claw to withdraw it from the notch A of the transport position and pivot the handle until the claw is engaged in the second notch B, so that the blade is in sufficient contact with the sheet to score it. The user then displaces the carriage in the direction of the arrow F 1 , by pulling the carriage, from the first edge  500   a  of the sheet  500  to the second edge  500   b  of the sheet  500 . During this movement, according to the arrow F 1 , the blade makes a score  501  in the layer of plaster of the sheet  500 . If this layer of plaster is covered with a sheet of paper or of cardboard, the blade cuts this sheet at the same time as its score the plaster. 
     During this movement, the user&#39;s only concern is to pull the carriage between the two edges of the sheet to score and cut this sheet. He does not have to worry about the position of the blade or its inclination. By virtue of this, the score is perfectly regular both in its form along the sheet and in its depth. 
     Having arrived at the second edge  500   b  of the sheet, the user folds the sheet along the score obtained in the preceding step to break the layer of plaster along the score. This folding in the direction of the arrows F 2  (see  FIG. 8 ) makes it possible to obtain a cutting edge  502  illustrated in  FIG. 9 . By virtue of the perfect straightness of the score, the cutting edge obtained is much more even than the cutting edges obtained by the cutter cutting method. 
     To further improve the flatness of this cutting edge, the carriage according to the invention offers a position of the handle, and therefore of the blade, which makes it possible to trim the cutting edge  502 . For this, as illustrated in  FIG. 9 , the user displaces the carriage using the gripping means from the second edge of the sheet to the first edge of the sheet, according to the arrow F 3 , then he actuates the retractable engaging claw to withdraw it from the second notch B and pivot the handle until the claw is engaged in the third notch C. In this position, the blade has a trimming edge pressed against the cutting edge obtained in the sheet folding step. The user once again displaces the carriage from the first edge  500   a  to the second edge  500   b , so that the cutting edge is trimmed by the blade. This step is illustrated in  FIGS. 10 and 11 . This last  FIG. 11  shows the untrimmed cutting edge  502  on the right of the figure and a trimmed cutting edge  502   a  on the left of the figure. Obviously, the cutting edge  503  of the scrap piece  504  from the sheet  500  is not trimmed in this step. 
     At the same time as the blade trims the cutting edge, it also cuts the sheet of paper or of cardboard positioned on the bottom face of the sheet of plasterboard, if such is present. 
     During this movement, the user does not have to worry about the position of the blade which is preset by the arrangement of the notch C. This angular position of the third notch C depends on the thickness of the sheet of plasterboard. In the example illustrated, the third notch C is spaced apart from the second notch B to allow for the trimming of a cutting edge of a sheet of plasterboard of a thickness e 1  (see  FIG. 11 ). 
     Advantageously, as illustrated in  FIG. 12 , the carriage comprises at least one additional notch (the notches D and E) at a distance from the third notch C to allow for the trimming of a cutting edge of a sheet of plasterboard of thickness e 2  or e 3  that are different from the thickness e 1  that can be trimmed when the trigger is engaged in the notch C. In  FIG. 12 , two additional notches are provided but, obviously, the person skilled in the art will be able to provide others thereof depending on the number of sheet thicknesses intended to be cut by the carriage according to the invention. For example, the notch C could make it possible to trim the edge of a sheet of plasterboard 10 mm thick, the notch D could make it possible to trim the edge of a sheet 13 mm thick (conventionally called, in France, “BA13 sheet”) and the notch E could make it possible to trim the cutting edge of a sheet 15 mm thick. Other notches could be provided for other thicknesses. 
     The implementation described previously is particularly effective when, according to the invention, a blade conforming to  FIGS. 14 to 21  is used with the carriage. 
     Unlike the cutter blade illustrated in  FIG. 13  and comprising a doubly beveled cutting edge, the carriage according to the invention advantageously contains a cutting blade  300  comprising at least one scoring corner  301  having, in cross-section, a planar face  300   a  and a beveled face  300   b  (see  FIG. 15 ). The corner is therefore defined by, on one side, a planar face, and on the other side, by a beveled face having two beveled edges  308 . The two beveled edges  308  are linked by at least one coupling line  309 . 
     This particular form of the cutting edge of the blade ensures a perfectly rectilinear scoring while preventing the blade from oscillating during the scoring, unlike what is observed with a cutter blade. 
     The beveled face makes it possible to cut the first sheet of cardboard and score the layer of plaster, and the planar face makes it possible to keep the blade in the same position during the scoring of the plaster. The inventor has observed that it is this maintaining of the position of the blade perpendicular to the sheet of plasterboard which makes it possible to obtain a perfectly rectilinear scoring and a cutting edge that is much more even than when using cutter blades. Since the latter are beveled on each face, it is very difficult, even impossible, even with a guide, to keep the blade in position, so that these cutter blades drift and the cutting edge that is consequently obtained is very uneven. 
     The best results have been obtained with an angle γ between the planar face and the beveled face of between 15 and 25 degrees, and preferably an angle γ of 20 degrees. Thus, when the bevel has such an angle, the blade remains perfectly rectilinear and does not oscillate during the scoring. Furthermore, the scoring obtained has a depth and a form such that, when the user folds the sheet of plasterboard (as in  FIG. 8 ), the edge obtained is much more even than that obtained with a cutter blade. 
     To further enhance the evenness and the flatness of the cutting edge, the blade also comprises a trimming edge  302  which also has a planar face and a beveled face. The trimming edge  302  has a length L 1  greater than or equal to the thickness of the sheet of plasterboard. If this thickness is denoted e, the length L 1  of the trimming edge must be greater than or equal to: e/sine β, β being the angle between the blade and the sheet of plasterboard when the trigger is engaged in the third notch C of the carriage (see  FIG. 6 ). Obviously, when the carriage comprises more than three notches (see  FIG. 12 ), the length L 1  of the trimming edge must be greater than or equal to the thickness of the sheet of plasterboard divided by the sine of the smallest angle β of the notches C, D or E. 
       FIG. 14   a  illustrates a variant of the blade of  FIG. 14 . 
     In this variant, the scoring corner  301  has a connecting facet  307  between the two beveled edges  308  of the scoring corner. 
     The connecting facet  307  is delimited by two coupling lines  309 , as well as by a coupling line  309   c  with the beveled face  300   b . The connecting facet  307  forms a plane making an angle δ with the planar face  300   a . The angle δ is less than the angle γ of the beveled edges  308  with the planar face  300   a . Advantageously, the angle δ is between 10 and 20, and preferably an angle δ of 15 degrees. The preferred embodiment is an angle γ of 20 degrees and an angle δ of 15 degrees. 
     The connecting face  307  facilitates the penetration of the blade into the sheet of plaster during the scoring and limits the forces during the maneuver. Furthermore, the inventor has noticed that the force that is exerted on the scrap part to break the sheet of plaster is also limited. 
     In practice, the connecting face  307  very substantially enhances the scoring obtained during the scoring step (see  FIG. 7 ). When the connecting face is absent, the single coupling line  309  can rub strongly against the plaster and tear away small pieces of plaster and paper or cardboard during the scoring. The scoring can therefore sometimes exhibit, in particular when the scoring is very rapid, scratches which cause, when the sheet is folded (see  FIG. 8 ), a not very even cutting edge. The connecting face  307  limits the friction between the scoring corner and the sheet, so that the score obtained is particularly even. It exhibits almost no scratches. The cutting edge obtained is very even and presents only very few protrusions, and protrusions of small sizes. The subsequent trimming step is therefore facilitated and constitutes only a finishing to obtain a perfectly planar cutting edge, with no protrusion hindering the positioning of two sheets one against the other. 
     This variant is applicable to the embodiments illustrated in  FIGS. 16 to 21 . 
     In a particularly advantageous embodiment illustrated in  FIG. 16 , the blade comprises, between the scoring corner  301  and the trimming edge  302 , a cutting notch  303 . This notch is useful when the sheet of plasterboard comprises a sheet of paper or cardboard on the bottom face of the sheet of plasterboard, in the cutting position. Thus, during the step of trimming the cutting edge, this sheet of paper or of cardboard is engaged in the notch  303  which allows for a clean and sharp cut of this sheet and prevents this sheet from being simply torn. Advantageously, to facilitate this cutting, the cutting notch is curved. 
     The concomitance of the trimming of the cutting edge and of the cutting of the bottom sheet of paper makes it possible to obtain a cut sheet of plasterboard with none of its sheets of paper torn and for which the cutting edge is free of any protuberance and perfectly parallel to the guide of the carriage used (therefore perfectly rectilinear if the guide is a straight rule). The juxtaposition of a number of sheets of plasterboard cut using the carriage according to the invention is therefore optimized, and the quantity of filler materials for the finishing operations is greatly limited. Furthermore, the fact that the sheets of paper or of cardboard are not torn, avoids having to fill the surface irregularities of the sheet of plasterboard. 
     In general, on a work site, it is necessary to perform numerous cuts of sheets of plasterboard. All these cuts wear the blade, so that the latter can, during the cutting movements (see  FIGS. 7 to 10 ) become blunt. The scoring is therefore no longer rectilinear and, when the user folds the sheet of cardboard (see  FIG. 8 ), the cutting edge may no longer be perfectly parallel to the guide and may exhibit great unevenness (presence of numerous protuberances). It is therefore necessary to change the blade. 
     One embodiment of a particularly advantageous blade is illustrated in  FIGS. 17 and 18 . In this embodiment, the four corners of the plate forming the blade are used as scoring corners. Each of these corners is extended by a trimming edge. Between each corner and the trimming edge, the blade bears a cutting notch. In this embodiment, two diametrically opposite scoring corners  311   a - 311   a  are symmetrical relative to the center of the rectangular plate forming the blade  310 . On the other hand, two consecutive scoring corners  311   a - 311   b  have a planar face and an opposite beveled face. This means, as illustrated in  FIG. 18 , that a scoring corner  311   a  has a beveled top face and a planar bottom face. On the other hand, a scoring corner  311   b  has a planar top face and a beveled bottom face. The same applies for the other structures that are the trimming edges  312   a  and  312   b  and the cutting notches  313   a  and  313   b.    
     According to the invention, the blade has a hole  315  intended to cooperate with a bolt provided with a nut  112   a  (see  FIG. 11 ) positioned in the recess  112  for receiving the blade of the carriage  100 . The blade  310  also comprises holes  316  intended to cooperate with fixed rods arranged in the recess  112  to secure the blade and prevent it from pivoting about the bolt  112   a . Obviously, any other means for fixing the blade in the recess can be used, provided that this fixing means firmly secures the blade at right angles to the sheet of plasterboard. 
     In this way, with a blade according to the invention, the planar face  300   a  of the blade  300  is held at right angles to the sheet of plasterboard during the scoring and trimming. 
     The embodiment of  FIG. 17  makes it possible to use the two scoring corners  311   a  by pivoting the blade about the hole  315  and to use the two scoring corners  311   b  by turning over the blade. Thus, with one and the same blade  310 , four scoring and trimming areas are obtained which can be used in succession when one of these areas is worn. 
     Obviously, as  FIGS. 19 and 20  show, the blade may bear only two areas each comprising a scoring corner, a trimming edge and a cutting notch. 
       FIG. 21  illustrates another embodiment of a blade according to the invention, suited both for left-handed users and for right-handed users. This blade  320  has four scoring corners  321 , four trimming edges  322  and four cutting notches  323 . In this embodiment, two diametrically opposite scoring corners are symmetrical relative to the center of the rectangular plate and two consecutive scoring corners have one and the same planar face and one and the same beveled face. With this embodiment, it is possible to manufacture a blade that can be used either from the left to the right, or from the right to the left. 
     To this end, it is possible to provide for the cutting carriage according to the invention to be dismantable and able to be configured either for a right-handed person or for a left-handed person. Thus, the section piece bearing the notches and the handle may be fixed to both sides of the chassis. When there is a protective cap, provision is also made for this cap to be able to be dismantled and fixed either for a right-handed person or for a left-handed person.  FIGS. 1 to 6  illustrate a suitable arrangement for use by a right-handed user. 
     In the embodiment of  FIG. 21 , the four corners are used to offer, to a right-handed user and to a left-handed user, two cutting areas that can be used in succession when the first to be used is worn. Obviously, it is possible to provide only one cutting area for a right-handed person and only one cutting area for a left-handed person. 
     The cutting carriage according to the invention comprises, advantageously, means for cooperating in a sliding manner with a cutting guide. A particularly suitable cutting guide has a profiled rail such as that which is illustrated in  FIG. 22 . In accordance with the invention, the guide of the carriage has two longitudinal edges  200   a  and two ends  200   b.    
     In a particularly advantageous embodiment, the guide  200  has a profiled rail  201 , intended to cooperate with the small wheels  102  of the carriage (see  FIGS. 1 and 22 ), this rail  201  being extended laterally by flats  202  increasing the contact surface area between the guide and the sheet of plasterboard. 
     The rail  201  may have any type of form. A particularly advantageous form, illustrated in  FIG. 22 , allows for a better stability and a better sliding hold of the carriage according to the invention. Around a longitudinal groove  203 , the rail  201  comprises two longitudinal protuberances  204 . Each of these protuberances has a part  201   a  intended to cooperate in a sliding manner with the small wheels  102  of the carriage  100 . Each part  201   a  comprises two non-coplanar rectilinear faces  205 - 206  linked by a flat  207  substantially at right angles to the contact face  208  of the guide  200  with the sheet of plasterboard. 
     The flats  202  have, preferably, a width L 2  set so that, in use, the cutting blade  300  is in tangential contact with the longitudinal edge  200   a  of one of the flats  202 . By virtue of this, the user can easily position the guide since all he needs to do is to align the edge of the flat with the cut marking line previously drawn by the user. Furthermore, the contact between the flat  202  and the blade prevents the latter from oscillating under the action of the movement of the carriage. If the blade used is in accordance with the invention, it is the planar face of the blade which is preferentially applied against the flat  202 , and not the beveled face. This further strengthens the guiding of the blade by optimizing the contact surface area between the blade and the guide. 
     Preferably, the cutting guide according to the invention can have securing means  209  arranged on the face  208  intended to be in contact with the sheet of plasterboard. As illustrated in  FIGS. 23 to 25 , these securing means may comprise spikes intended to be driven into the plaster of the sheet of plasterboard. 
     Thus, when the user has positioned the guide in the desired manner, all he needs to do is to press on this guide for the spikes of the securing means to be driven into the sheet and prevent, during the different cutting steps (see  FIGS. 7 to 10 ) the guide from moving from its position of use. 
     In the embodiment of  FIG. 25 , the spikes are borne by rods  209   b.    
     Advantageously, the securing means are retractable to prevent the spikes from injuring the user when the guide is not in use. In the embodiment of  FIGS. 23 and 24 , these spikes are borne by screws  209   a . The screws are preferably inserted into the longitudinal groove  203 . When the user wants to use the guide, he withdraws the screws from the plane of the surface  208  using a screwdriver. When the user has finished the cuts, he unscrews the screws until they leave the plane of the surface  208 . Advantageously, these screws have a length such that, when they are not screwed, they are held in the groove  203  and prevent the cooperation of the carriage with the rail. 
     Any other means that can render the spikes retractable can be used in the guide according to the invention. 
     Preferably, the securing means  209  are arranged on the face  208  of the guide so that, in use, after the cutting of the sheet of plasterboard, the holes formed by the spikes driven into the sheet of plasterboard are situated at a determined distance d from the cut, sufficient for the holes to be filled at the same time as a join between two sheets of plasterboard. 
     For example, the securing means  209  are arranged at the distance d from the edge  200   a  of the flat  202 . 
     Conventionally, the finishing operations are performed using a coating knife of a width of between 150 mm and 300 mm. 
     Thus, the spikes of the securing means will preferentially be arranged at a determined distance of between 75 mm and 150 mm, preferably between 70 mm and 120 mm, advantageously between 55 mm and 80 mm, typically 65 mm. 
     Advantageously, the cutting guide comprises, at least at one of the ends  200   b  of the rail  201 , an abutment  210  mounted to rotate relative to the rail  201 . Advantageously, the abutment is provided with means for securing, in use, against the sheet of plasterboard. In the embodiment illustrated in  FIG. 26 , this securing means comprises a spike  211  intended to be driven into the thickness of the sheet of plasterboard. Thus, the user positions the abutment  210  against an edge of the sheet of plasterboard, and secures this abutment against this sheet by driving the spike  211  into the thickness of the sheet of plasterboard. Then, since the abutment  210  is mounted to rotate relative to the rail  201 , he can position the guide angularly according to his choice on the sheet of plasterboard as illustrated in  FIG. 29 . 
     The securing means may be retractable. For example, a spike  211  is borne by a screw. 
     Preferably, the rotary mounting of the abutment  210  relative to the rail  201  can be controlled using a thumb wheel  212 . 
     According to a particularly advantageous embodiment, the abutment  210  according to the invention comprises two parts linked to one another by an articulation. This embodiment is illustrated in  FIGS. 27 and 28 . 
     In these figures, the abutment  220  comprises a part  221  similar to the abutment  210  of  FIG. 26 , and a part  222  linked to the part  221  by an articulation  223 . The two articulated parts  221  and  222  are provided with means  211  for securing the sheet of plasterboard. In  FIG. 27 , the securing means of the articulated part  222  comprise spikes  211 . In  FIG. 28 , the securing means comprise a plate  211   a  arranged to allow the sheet of plasterboard to be held between this plate  211   a  and a protuberance  211   b  of the articulated part  222 . This arrangement can be obtained by producing the articulated part  222  in a single profiled structure. 
     The abutment  210  advantageously comprises an end-of-rotation abutment allowing a limited rotation of the articulated parts  221  and  222 . In practice, the end-of-rotation abutment advantageously limits the rotation between 0 and 45 degrees, and preferably between 0 and 30 degrees. 
     By virtue of these articulated parts of the means for securing the sheet of plasterboard, and of the end-of-rotation abutment, the user can on his own perform a cut of a sheet of plasterboard of large size with no risk that the scrap piece  504  (see  FIG. 11 ) will fall during the trimming step, thus tearing the bottom sheet of paper and/or being broken. 
     In practice, when the user breaks the sheet along the score (see  FIG. 8 ) and commences the trimming of the cutting edge (see  FIGS. 10 and 11 ), the end of the scrap piece  504  already freed is held by the articulated part  222 . 
     According to other embodiments that are not illustrated, the rail of the guide may comprise a retractable stop means to allow, in use, the coupling and the decoupling of the rail with respect to the carriage. Thus, when the carriage is coupled to the rail, the retractable stop means prevents, in the movement, the carriage from leaving the rail. After use, to facilitate transport, it is desirable to decouple the carriage and the rail. The user then deactivates the retractable stop means and removes the carriage from the rail. For example, a pin provided with a return means can be used as retractable stop means. 
     It is also possible, alternatively or in combination, to provide at least one of the ends of the rail with a means for damping, in use, the sliding of the carriage at end of travel. Thus, the carriage cannot violently strike the retractable stop means or, the carriage cannot violently leave the rail. For example, it is possible to use a spring or a piston as damping means.