PLANETARY TYPE DRAWING TABLE
United States Patent 3789777
A drawing table of planetary type. The drawing board performs general rotational movements about a fixed pivot with vertical axis which acts as a support base, and rotational movements on itself about a vertical axis, in the manner of a planet around the sun. The table comprises a fixed pivot with vertical axis, referred to as a column, a radial arm, referred to as a support arm, which turns in a horizontal plane about said pivot, and a board which is mounted rotatably about a vertical axis at the end of the support arm.
US Patent References:
Connecting device for drawing-table tops and standards
Fraser - March 1925 - 1529022
Bedside stand and tray
Wells - September 1952 - 2609938
Mounting structure sensitive to the direction of movement of the mounted object, and clutch incorporated therein
Batori - June 1957 - 2795299
Pedestal drafting table or the like
Murray - July 1952 - 2601998
Reading stand
Brossard - January 1965 - 3167036
Connecting device for drawing-table tops and standards
Fraser - March 1925 - 1529022
Bedside stand and tray
Wells - September 1952 - 2609938
Mounting structure sensitive to the direction of movement of the mounted object, and clutch incorporated therein
Batori - June 1957 - 2795299
Pedestal drafting table or the like
Murray - July 1952 - 2601998
Reading stand
Brossard - January 1965 - 3167036
Application Number:
05/194855
Publication Date:
02/05/1974
Filing Date:
11/02/1971
View Patent Images:
Export Citation:
Primary Class:
International Classes:
A47B27/02; A47B27/18; A47B27/00; A47F5/12
Field of Search:
108/2-10
US Patent References:
Primary Examiner:
Gilliam, Paul R.
Assistant Examiner:
Finch G. O.
Attorney, Agent or Firm:
Eric, Waters Et Al H.
Claims:
1. A drawing table comprising a fixed pivot column, extending along a vertical axis, a radial support arm which is rotatable in a horizontal plane about said column, a board, means permitting the board to be oriented around a vertical axis on the free end of said support arm, means for adjusting the height of said support arm on said column, and means for arresting said height adjustment means, said height adjustment means comprising a shaft which is slidable vertically in said column and which carries said support arm, said arresting means comprising a vertical threaded rod which is fixed to said column, a nut portion which is slidable transversely in the shaft, a spring in the shaft for applying the nut portion against the threaded rod, and means for adjustment of the horizontality of the support arm including at least one vertical threaded pin which is screwed in the support arm and a thrust bearing under the end
2. A drawing table comprising a fixed pivot column, extending along a vertical axis, a radial support arm which is rotatable in a horizontal plane about said column, a board, means permitting the board to be oriented around a vertical axis on the free end of said support arm, means for adjusting the height of said support arm on said column, and means for arresting said height adjustment means, said height adjustment means comprising a shaft which is slidable vertically in said column and which carries said support arm, said arresting means comprising a vertical threaded rod which is fixed to said column, a nut portion which is slidable transversely in the shaft, a spring in the shaft for applying the nut portion against the threaded rod, and means for arresting the rotary movement of the support arm including two alternate sets of horizontal discs, the discs of a first set being to the shaft and a vertical screw which carries the discs of the second set and which is screwed in the
3. A drawing table comprising a fixed pivot column extending along a vertical axis, a radial support arm which is rotatable in a horizontal plane about said column, a board, means permitting the board to be oriented around a vertical axis on the end of said support arm, means for adjusting the height of said support arm on said column, and means for arresting said height adjustment means, said height adjustment means comprising a shaft which is slidable vertically in said column and which carries said support arm, said arresting means comprising a vertical threaded rod which is fixed to said column, a nut portion which is slidable transversely in the shaft, and a spring in the shaft for applying the nut portion against the threaded rod, and means for arresting said board orienting means including two vertical alternate sets of discs which are concentric with said inclining axis, the discs of a first set being fixed to the board, the discs of the second set being fixed to said orienting means, a ring for tightening said discs against each other, a transverse adjustment shaft having an eccentric, which bears against the ring, a crank arm on said eccentric, a transverse actuating shaft having an eccentric within the crank arm, and on said shaft, a lever having a
4. A table according to claim 2 wherein said shaft comprises a spindle portion of rectangular section and two plates with pointed screws, the discs of the first set having a central rectangular aperture disposed on
5. A table according to claim 3 wherein said discs are provided with lugs, the lugs of the discs of the first set being disposed in a recess in the board and the lugs of the discs of the second set being disposed in a recess in said orientation means.
2. A drawing table comprising a fixed pivot column, extending along a vertical axis, a radial support arm which is rotatable in a horizontal plane about said column, a board, means permitting the board to be oriented around a vertical axis on the free end of said support arm, means for adjusting the height of said support arm on said column, and means for arresting said height adjustment means, said height adjustment means comprising a shaft which is slidable vertically in said column and which carries said support arm, said arresting means comprising a vertical threaded rod which is fixed to said column, a nut portion which is slidable transversely in the shaft, a spring in the shaft for applying the nut portion against the threaded rod, and means for arresting the rotary movement of the support arm including two alternate sets of horizontal discs, the discs of a first set being to the shaft and a vertical screw which carries the discs of the second set and which is screwed in the
3. A drawing table comprising a fixed pivot column extending along a vertical axis, a radial support arm which is rotatable in a horizontal plane about said column, a board, means permitting the board to be oriented around a vertical axis on the end of said support arm, means for adjusting the height of said support arm on said column, and means for arresting said height adjustment means, said height adjustment means comprising a shaft which is slidable vertically in said column and which carries said support arm, said arresting means comprising a vertical threaded rod which is fixed to said column, a nut portion which is slidable transversely in the shaft, and a spring in the shaft for applying the nut portion against the threaded rod, and means for arresting said board orienting means including two vertical alternate sets of discs which are concentric with said inclining axis, the discs of a first set being fixed to the board, the discs of the second set being fixed to said orienting means, a ring for tightening said discs against each other, a transverse adjustment shaft having an eccentric, which bears against the ring, a crank arm on said eccentric, a transverse actuating shaft having an eccentric within the crank arm, and on said shaft, a lever having a
4. A table according to claim 2 wherein said shaft comprises a spindle portion of rectangular section and two plates with pointed screws, the discs of the first set having a central rectangular aperture disposed on
5. A table according to claim 3 wherein said discs are provided with lugs, the lugs of the discs of the first set being disposed in a recess in the board and the lugs of the discs of the second set being disposed in a recess in said orientation means.
Description:
BACKGROUND AND NATURE OF THE INVENTION
The invention also concerns various improvements in the above mentioned drawing tables. The improvements concern the arresting of the vertical movement of the support arm on the column, actuation of the arresting means, adjustment of the horizontality of the support arm, arresting of the rotary movement of the support arm on the column, and arresting of the inclination of the board with means for controlling same.
Briefly, the vertical movement can be arrested, in accordance with the invention, by the engagement on a vertical threaded rod which is rigidly fixed to the column, of a portion (for example less than half) of a nut which is slidable transversely under the action of a spring in the shaft carrying the support arm.
Briefly, in accordance with the invention the arresting of the vertical movement can be controlled by a flexible cable which moves said nut portion away from the threaded rod, and the flexible cable control handle is slidable in grooves in the lower edge of the board.
Briefly, adjustment of the horizontality of the support arm can be effected, in accordance with the invention, by at least one vertical threaded pin which is screwed in the support arm, thrusting against a thrust bearing supported on the end of the shaft.
Briefly, in accordance with the invention, arresting of the rotary movement of the support arm can be effected by the mutual friction between two alternate sets of discs, some of which are rigidly fixed to the shaft while the others are mounted in the support arm on a screw, the screwing movement of which tightens the discs against each other.
Briefly, in accordance with the invention, arresting the inclining movement of the board can be effected by the mutual friction between two alternate sets of concentric discs, some of which are rigidly fixed to the board while the others are rigidly fixed to the board orientation means, the discs being tightened against each other by a ring in which there is transversely pivoted an eccentric adjustment shaft, and by a crank arm between said eccentric and an eccentric on a shaft which is pivotable transversely at the end of the inclining shaft, under the action of an arresting lever, the handle of which is displaced under the edge of the drawing board.
The invention, and embodiments thereof, will be described with reference to the following drawings given by way of non-limitative examples:
FIGS. 1 to 10 are diagrammatic plan views showing the table according to the invention with the board in various positions relative to the support means;
FIGS. 11 to 13 show an embodiment of the invention, FIG. 11 being a diagrammatic elevational overall view, FIG. 12 being an elevational view perpendicular to the view of FIG. 11, and FIG. 13 being a plan view;
FIG. 14 is a detail in cross-section of the region comprising the article of furniture and the arm of the embodiment shown in FIGS. 11 to 13;
FIG. 15 is a plan view with part broken away, FIG. 16 is a front elevation, and FIG. 17 is a rear elevation: these three Figures situate on the drawing table the improvements according to the invention;
FIG. 18 is an axial section of the means for arresting the vertical movement of the board according to the invention;
FIG. 19 is a cross-section taken along the line XIX--XIX of FIG. 18;
FIG. 20, which is similar to FIG. 19, corresponds to the released position of the arresting means shown in FIGS. 18 and 19;
FIG. 21, which is similar to FIG. 16, FIG. 22 which is similar to FIG. 18, and the detail shown in FIG. 23, illustrate the means for controlling the above mentioned arresting of the vertical movement, in accordance with the invention;
FIG. 24 shows a vertical section of the means for adjusting the horizontality of the support arm according to the invention;
FIG. 25 shows a vertical axial section of the means for arresting the rotary movement of the support arm according to the invention;
FIG. 26 is a cross-section taken along the line XXVI--XXVI of FIG. 25;
FIG. 27 is an axial cross-section, and FIG. 28 is an end view, of the means for arresting the inclining movement of the board, with the actuating means thereof, in accordance with the invention.
The advantages of the planetary table according to the invention will be clearly apparent from FIGS. 1 to 10 which are diagrammatic plan views showing various positions of the drawing board relative to the support means, the direction of work on the board being indicated by an arrow F; for example the board 1 can be turned so as to face towards the right, and positioned against the desk 2 (FIG. 1), or in front of the desk 2 (FIG. 2), or to the right in front of the desk (FIG. 3), or to the right beside the desk 2 (FIG. 4); the board 1 can likewise be turned to face towards the left, against the desk 2 (FIG. 5), which is a position in which it takes up the minimum amount of space, or beside the desk 2 (FIG. 6), or it can be turned to 90° on one side (FIGS. 7 and 8) or the other (FIGS. 9 and 10). Thus, the user of the drawing table can position the board as he wishes, irrespective of the conditions of his environment, such as the direction of the light or lights.
Referring to FIGS. 11, 12 and 13 which show a drawing table according to the invention, and to the detail view shown in FIG. 14: the article of furniture 2 is preferably provided with a ballast weight 3 in order to stabilise the article 2 in spite of the cantilever weight of the board 1 and the weight applied thereto by the user who might rest thereon. Close to the angle adjacent the angle in which the ballast weight 3 is housed, the article of furniture 2 is provided with a height adjustment means which can be of any known type: for example it can comprise a telescopic shaft 4 which is mounted on rollers in the column 5, compensated by a pneumatic spring 6, and actuated by a motor 7 and transmission 8. At its upper end the height adjustment means is provided with a pivot assembly 11 with vertical axis 12; the pivot assembly 11 can comprise a spindle portion 13 which is rigidly fixed with the shaft 4, and two discs which are rigidly fixed to the radial arm or support arm 21, one disc 14 being at the top and the other disc 15 being at the bottom; the disc 15 can be knurled on its lower face which bears by way of plastics washer 16 on the upper knurled face of a non-rotatable portion 17 of the shaft 4; a hand control lever 18 locks the radial arm 21, by tightening the above described assembly. At its other end, the radial support arm 21 carries the board 1 by way of per se known orientation means 22 with control hand lever 23 and inclining means 24 with control hand lever 25.
With reference to the three FIGS. 15, 16, and 17: these figures show the drawing board 1, the support arm 21 and the column 5 which is rigidly fixed to the article of furniture 2: improvements according to the invention will now be described, namely the means for arresting the vertical movement of the support arm 21 on the column 5, the means for controlling the arresting means, the means for adjusting the horizontality of the support arm 21, the means for arresting the rotary movement of the support arm 21 on the column 5, and the means for arresting the inclining movement of the board 1 with the actuation means thereof.
With reference to FIGS. 18, 19 and 20, which show the means for arresting the vertical movement of the board: between two side plates 31 the columns 5 carries a threaded rod 32; the telescopic shaft 4 which is slidable vertically with the support arm 21 relative to the column 5, is provided with a bush 33 in which a portion, for example a little less than half, of a nut 34, is transversely slidable. A spring 39 urges the nut 34 against the threaded rod 32, which ensures precise arresting without play (FIG. 19). To permit the vertical movement, the nut 34 is moved away from the threaded rod 32 (FIG. 20) by a flexible cable 35 of the known type referred to as a Bowden cable, the movement of the nut 34 away from the rod 32 being limited by a stud 36 which is fixed to the nut 34 and which is slidable in an elongate aperture 37 in the bush 33. When eventually the threaded rod 32 shows signs of wear in its portion which is in contact with the nut 34, it has only to be turned about itself, for example by means of a recess 38 in its head and a screw-driver. The threaded rod 32 preferably has a triangular thread, which contributes to ensuring that arresting occurs without play, positively and irreversibly. The efficiency and the simplicity, as well as the economy, of the means used, will be noted.
Referring to FIGS. 21, 22 and 23, which show the means for actuating the vertical movement arresting means described above: the flexible cable 35 ends in a sleeve 41 having lugs 42 (FIG. 23) which are slidable in grooves 43 in the lower edge of the board 1; the handle 44 of the sleeve 41, which actuates the cable 35 and the nut 34, is thus movable along the lower edge of the board 1 (FIG. 19), and is always immediately accessible.
Referring now to FIG. 24: this figure shows the vertical shaft 4 (which is slidable vertically relative to the column 5), with its spindle portion 13 on which the support arm 21 is pivoted. Horizontally of the radial arm 21 is ensured by one (or more) vertical threaded pins 46 which are screwable at 47 in the radial support arm 21, thrusting against a thrust bearing 48 supported on the end of the shaft 4. This adjustment of the horizontality of the support arm 21 makes it possible to set the upper and lower edges of the drawing board in a precisely horizontal position, which is essential for the good operation of conventional drawing equipment.
Referring to FIGS. 25 and 26: the support arm 21 is pivoted, on the spindle portion 13 of the vertical shaft 4, by a roller bearing 51 on which it is a force fit, and by a ring 52 made of self-lubricating material. The rotary movement of the support arm 21 on the vertical shaft 4 is arrested by the mutual friction when tightened together, between the faces of two alternate sets of discs 53 and 54; the discs 53 which have a rectangular central aperture are mounted, by means of two plates 55 and pointed screws 56, on a rectangular part of the spindle portion 13, so that they are non-rotatably secured on the spindle portion 13 which is also non-rotatable; the discs 54 are held in the support arm 21 by a gripping screw 57 which is screwed in a ring 58 fixed to the arm 21; the arresting action is applied and released by operating a removable key (not shown) which is inserted into a recess 59 in the screw 57 when the user wishes to change the orientation of the support arm 21 and the drawing board.
Referring to FIGS. 27 and 28: inclination of the board 1 by rotation about the shaft 24, is arrested by the mutual friction when tightened together between the faces of two alternate sets of concentric discs 61 and 62. The discs 61 are fixed to the board 1 by lugs 63 which are housed in a recess 64 in the support 65 of the board. The discs 62 are fixed to the support 66 (of the means 22 for orienting the board 1), by means of lugs 67 which are housed in a recess 68 in the support 66; the discs 61 and 62 are tightened together by means of a ring 71 which is slidable on the shaft 24 and in which a shaft 72 forming at the centre an eccentric 73 is transversely pivotable. The eccentric 73 is connected by a crank arm 74 to another eccentric 75 of a shaft 76 which is pivotable at the end of the shaft 24 under the action of a control lever 77. A basic adjustment being effected by means of the eccentric 73, the inclining movement of the board 1 is arrested and released by means of the eccentric 75, actuated by the lever 77. The handle 78 of the lever 77 (FIGS. 15 and 16) is displaced below the lower edge of the board 1, close to said lower edge and parallel to the board, so that operation thereof is practical and is also immediately accessible.
The invention also concerns various improvements in the above mentioned drawing tables. The improvements concern the arresting of the vertical movement of the support arm on the column, actuation of the arresting means, adjustment of the horizontality of the support arm, arresting of the rotary movement of the support arm on the column, and arresting of the inclination of the board with means for controlling same.
Briefly, the vertical movement can be arrested, in accordance with the invention, by the engagement on a vertical threaded rod which is rigidly fixed to the column, of a portion (for example less than half) of a nut which is slidable transversely under the action of a spring in the shaft carrying the support arm.
Briefly, in accordance with the invention the arresting of the vertical movement can be controlled by a flexible cable which moves said nut portion away from the threaded rod, and the flexible cable control handle is slidable in grooves in the lower edge of the board.
Briefly, adjustment of the horizontality of the support arm can be effected, in accordance with the invention, by at least one vertical threaded pin which is screwed in the support arm, thrusting against a thrust bearing supported on the end of the shaft.
Briefly, in accordance with the invention, arresting of the rotary movement of the support arm can be effected by the mutual friction between two alternate sets of discs, some of which are rigidly fixed to the shaft while the others are mounted in the support arm on a screw, the screwing movement of which tightens the discs against each other.
Briefly, in accordance with the invention, arresting the inclining movement of the board can be effected by the mutual friction between two alternate sets of concentric discs, some of which are rigidly fixed to the board while the others are rigidly fixed to the board orientation means, the discs being tightened against each other by a ring in which there is transversely pivoted an eccentric adjustment shaft, and by a crank arm between said eccentric and an eccentric on a shaft which is pivotable transversely at the end of the inclining shaft, under the action of an arresting lever, the handle of which is displaced under the edge of the drawing board.
The invention, and embodiments thereof, will be described with reference to the following drawings given by way of non-limitative examples:
FIGS. 1 to 10 are diagrammatic plan views showing the table according to the invention with the board in various positions relative to the support means;
FIGS. 11 to 13 show an embodiment of the invention, FIG. 11 being a diagrammatic elevational overall view, FIG. 12 being an elevational view perpendicular to the view of FIG. 11, and FIG. 13 being a plan view;
FIG. 14 is a detail in cross-section of the region comprising the article of furniture and the arm of the embodiment shown in FIGS. 11 to 13;
FIG. 15 is a plan view with part broken away, FIG. 16 is a front elevation, and FIG. 17 is a rear elevation: these three Figures situate on the drawing table the improvements according to the invention;
FIG. 18 is an axial section of the means for arresting the vertical movement of the board according to the invention;
FIG. 19 is a cross-section taken along the line XIX--XIX of FIG. 18;
FIG. 20, which is similar to FIG. 19, corresponds to the released position of the arresting means shown in FIGS. 18 and 19;
FIG. 21, which is similar to FIG. 16, FIG. 22 which is similar to FIG. 18, and the detail shown in FIG. 23, illustrate the means for controlling the above mentioned arresting of the vertical movement, in accordance with the invention;
FIG. 24 shows a vertical section of the means for adjusting the horizontality of the support arm according to the invention;
FIG. 25 shows a vertical axial section of the means for arresting the rotary movement of the support arm according to the invention;
FIG. 26 is a cross-section taken along the line XXVI--XXVI of FIG. 25;
FIG. 27 is an axial cross-section, and FIG. 28 is an end view, of the means for arresting the inclining movement of the board, with the actuating means thereof, in accordance with the invention.
The advantages of the planetary table according to the invention will be clearly apparent from FIGS. 1 to 10 which are diagrammatic plan views showing various positions of the drawing board relative to the support means, the direction of work on the board being indicated by an arrow F; for example the board 1 can be turned so as to face towards the right, and positioned against the desk 2 (FIG. 1), or in front of the desk 2 (FIG. 2), or to the right in front of the desk (FIG. 3), or to the right beside the desk 2 (FIG. 4); the board 1 can likewise be turned to face towards the left, against the desk 2 (FIG. 5), which is a position in which it takes up the minimum amount of space, or beside the desk 2 (FIG. 6), or it can be turned to 90° on one side (FIGS. 7 and 8) or the other (FIGS. 9 and 10). Thus, the user of the drawing table can position the board as he wishes, irrespective of the conditions of his environment, such as the direction of the light or lights.
Referring to FIGS. 11, 12 and 13 which show a drawing table according to the invention, and to the detail view shown in FIG. 14: the article of furniture 2 is preferably provided with a ballast weight 3 in order to stabilise the article 2 in spite of the cantilever weight of the board 1 and the weight applied thereto by the user who might rest thereon. Close to the angle adjacent the angle in which the ballast weight 3 is housed, the article of furniture 2 is provided with a height adjustment means which can be of any known type: for example it can comprise a telescopic shaft 4 which is mounted on rollers in the column 5, compensated by a pneumatic spring 6, and actuated by a motor 7 and transmission 8. At its upper end the height adjustment means is provided with a pivot assembly 11 with vertical axis 12; the pivot assembly 11 can comprise a spindle portion 13 which is rigidly fixed with the shaft 4, and two discs which are rigidly fixed to the radial arm or support arm 21, one disc 14 being at the top and the other disc 15 being at the bottom; the disc 15 can be knurled on its lower face which bears by way of plastics washer 16 on the upper knurled face of a non-rotatable portion 17 of the shaft 4; a hand control lever 18 locks the radial arm 21, by tightening the above described assembly. At its other end, the radial support arm 21 carries the board 1 by way of per se known orientation means 22 with control hand lever 23 and inclining means 24 with control hand lever 25.
With reference to the three FIGS. 15, 16, and 17: these figures show the drawing board 1, the support arm 21 and the column 5 which is rigidly fixed to the article of furniture 2: improvements according to the invention will now be described, namely the means for arresting the vertical movement of the support arm 21 on the column 5, the means for controlling the arresting means, the means for adjusting the horizontality of the support arm 21, the means for arresting the rotary movement of the support arm 21 on the column 5, and the means for arresting the inclining movement of the board 1 with the actuation means thereof.
With reference to FIGS. 18, 19 and 20, which show the means for arresting the vertical movement of the board: between two side plates 31 the columns 5 carries a threaded rod 32; the telescopic shaft 4 which is slidable vertically with the support arm 21 relative to the column 5, is provided with a bush 33 in which a portion, for example a little less than half, of a nut 34, is transversely slidable. A spring 39 urges the nut 34 against the threaded rod 32, which ensures precise arresting without play (FIG. 19). To permit the vertical movement, the nut 34 is moved away from the threaded rod 32 (FIG. 20) by a flexible cable 35 of the known type referred to as a Bowden cable, the movement of the nut 34 away from the rod 32 being limited by a stud 36 which is fixed to the nut 34 and which is slidable in an elongate aperture 37 in the bush 33. When eventually the threaded rod 32 shows signs of wear in its portion which is in contact with the nut 34, it has only to be turned about itself, for example by means of a recess 38 in its head and a screw-driver. The threaded rod 32 preferably has a triangular thread, which contributes to ensuring that arresting occurs without play, positively and irreversibly. The efficiency and the simplicity, as well as the economy, of the means used, will be noted.
Referring to FIGS. 21, 22 and 23, which show the means for actuating the vertical movement arresting means described above: the flexible cable 35 ends in a sleeve 41 having lugs 42 (FIG. 23) which are slidable in grooves 43 in the lower edge of the board 1; the handle 44 of the sleeve 41, which actuates the cable 35 and the nut 34, is thus movable along the lower edge of the board 1 (FIG. 19), and is always immediately accessible.
Referring now to FIG. 24: this figure shows the vertical shaft 4 (which is slidable vertically relative to the column 5), with its spindle portion 13 on which the support arm 21 is pivoted. Horizontally of the radial arm 21 is ensured by one (or more) vertical threaded pins 46 which are screwable at 47 in the radial support arm 21, thrusting against a thrust bearing 48 supported on the end of the shaft 4. This adjustment of the horizontality of the support arm 21 makes it possible to set the upper and lower edges of the drawing board in a precisely horizontal position, which is essential for the good operation of conventional drawing equipment.
Referring to FIGS. 25 and 26: the support arm 21 is pivoted, on the spindle portion 13 of the vertical shaft 4, by a roller bearing 51 on which it is a force fit, and by a ring 52 made of self-lubricating material. The rotary movement of the support arm 21 on the vertical shaft 4 is arrested by the mutual friction when tightened together, between the faces of two alternate sets of discs 53 and 54; the discs 53 which have a rectangular central aperture are mounted, by means of two plates 55 and pointed screws 56, on a rectangular part of the spindle portion 13, so that they are non-rotatably secured on the spindle portion 13 which is also non-rotatable; the discs 54 are held in the support arm 21 by a gripping screw 57 which is screwed in a ring 58 fixed to the arm 21; the arresting action is applied and released by operating a removable key (not shown) which is inserted into a recess 59 in the screw 57 when the user wishes to change the orientation of the support arm 21 and the drawing board.
Referring to FIGS. 27 and 28: inclination of the board 1 by rotation about the shaft 24, is arrested by the mutual friction when tightened together between the faces of two alternate sets of concentric discs 61 and 62. The discs 61 are fixed to the board 1 by lugs 63 which are housed in a recess 64 in the support 65 of the board. The discs 62 are fixed to the support 66 (of the means 22 for orienting the board 1), by means of lugs 67 which are housed in a recess 68 in the support 66; the discs 61 and 62 are tightened together by means of a ring 71 which is slidable on the shaft 24 and in which a shaft 72 forming at the centre an eccentric 73 is transversely pivotable. The eccentric 73 is connected by a crank arm 74 to another eccentric 75 of a shaft 76 which is pivotable at the end of the shaft 24 under the action of a control lever 77. A basic adjustment being effected by means of the eccentric 73, the inclining movement of the board 1 is arrested and released by means of the eccentric 75, actuated by the lever 77. The handle 78 of the lever 77 (FIGS. 15 and 16) is displaced below the lower edge of the board 1, close to said lower edge and parallel to the board, so that operation thereof is practical and is also immediately accessible.