Drafting Board Base

The invention relates to a drafting board base which is used to support a working surface, for example, for drafting or drawing purposes. The base includes an upright column which supports the drafting or drawing board proper in a load relieved manner. Conventionally, the board forming the working surface is adjustable in the three directions of space to take up different elevational positions as well as different angular positions relative to the horizontal and also different rotational positions relative to the vertical. In each of these positions, the board may be locked after proper adjustment.

The rigid locking devices which have been employed heretofore are subject to damage if the board should be exposed to excessive loads.

In view of the foregoing, it is the aim of the invention to achieve the following objects, singly or in combination:

to construct a base for a drawing or drafting board wherein the adjustment mechanism may not be damaged even if heavy loads should be applied;

to provide an adjustment mechanism for a drafting or drawing board which is of simple and light construction and which permits a rapid adjustment;

to include in the adjustment and safety or locking mechanism slipping means such as a slipping clutch which will protect the adjustment mechanism against overloads; and

to substantially improve the useful life of a drafting apparatus according to the invention.

According to the invention there is provided a base for a drafting or drawing board which base comprises an upright column for carrying the board in a load relieved manner. The board is adjustable and securable in its elevational position. Further, the board is rotatable and tiltable relative to that portion of the upright column which is adjustable in the elevational position. Brake elements are provided for the securing of the elevational position of the board. Further brake elements are provided for securing the position against rotation about the vertical, longitudinal column axis. Third brake elements are provided for securing the board in its tilted position after the board has been tilted about the horizontal rotational support. These brake elements are so adjusted or adjustable that a slipping of the brake elements is made possible even before a permissible load is reached especially when the board is subject to a load or stress not normally intended and hence improper.

The combination of three brake mechanisms which respond to excessive loads by a slipping action results in an especially simple structure of the drafting board base while simultaneously protecting the structure against overloads.

In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates the drawing or drafting board base according to the invention in a vertical, axial section, whereby the board is shown in its lowered down position;

FIG. 2 illustrates the upper portion of the base and parts of the board whereby the latter is in its elevated position;

FIG. 3 is a longitudinal section through the horizontal tilting bearing of the drafting board or table along the section line III--III in FIG. 1;

FIG. 4 is an elevational view of an arm of a pedal for operating the present mechanism including a sectional view through respective brake elements;

FIG. 5 is a horizontal sectional view through the upright column shown in FIG. 1 along section line V--V; and

FIG. 6 shows the tilting bearing element of FIG. 3 in a perspective view for tilting and holding a drawing board or the like.

Referring to FIG. 1 there is shown an upright column 1 secured to a pedestal forming together the base proper. The upright column 1 comprises a hollow sectional member inside of which there is arranged a hollow column 4 carrying at its top the table or board 3. The hollow column 4 is adjustable in its elevational position and secured against rotation by guide means inside the upright column 1. The guide means comprise two longitudinal guide grooves 5 arranged in the hollow column 4 at two oppositely positioned longitudinal edges thereof. Adjacent corners of the hollow column 4 form corner guide grooves 6 which receive balls 7, whereby the inner hollow column 4 is guided without any play. Two brake plates 9 rest against the hollow column 4 which is adjustable in its elevational position. These brake plates 9 make it possible to block the hollow column 4 relative to the upright column 1 when the hollow column 4 is in its extended position. The brake pressure is exerted by means of a spring bail 8 having a U-configuration. The bail 8 is constructed as a brake pedal. The bail 8 is provided at its upper end with legs 8' into which there are inserted pressure bolts 18 forming the tilting axis of the bail 8. The pressure bolts 8 extend through a respective bore in the bearing plate 39. The bearing plates are guided in openings 17 arranged opposite each other in the outer hollow upright column 1. The spring elastic legs 8' of the bail 8 press the bolts 18 against the brake plates 9 which in turn rest against the inner hollow column 4. Conical discs 19 are arranged on a bearing plate 39 below the pressure bolts 18 and on the outer surface of the upright column 1. In operation, when the bail 8 is tilted toward the upright column 1, that is in the direction of the arrow A, the bail legs 8' are spread apart and the brake plates 9 are relieved from the brake load. Thus, the elevational position of the drafting board 3 is possible. Upon release of the bail 8, the latter simultaneously tilts back into the original position due to its inherent spring characteristic, whereby the brake plates 9 are again subjected to the full brake load. Incidentally, in FIG. 1 the brake position of the bail 8 is shown in full lines and the release position of the bail 8 is shown in dash-dotted lines.

As best seen in FIG. 2, the drawing or drafting board 3 which is rotatable about the vertical axis X--X, shown in FIG. 1, reaches with a vertically extending, conical brake piston 10 into a respectively shaped conical recess formed in a support member 11 which is rigidly secured to the hollow column 4. The conical brake piston 10 is secured to the board 3. The axially upwardly facing end of the brake piston 10 is provided with an axially extending recess 20. A spring element 12 functioning as a clamping disc is located in the recess 20. A clamping screw 21 extends through the spring element 12. The spring element 12 is effective against the bottom of the depression 20 of the brake piston 10 through the head 21' of the clamping screw 21 and through the axial bearing 12'. The conical brake piston 10 is thus pressed into the hollow conical recess in the support member 11, whereby the brake pressure is produced. The brake pressure may be adjusted as desired by adjusting the clamping screw 21, whereby a slip-type clutch function is accomplished so that the drafting or drawing board 3 may be rotated about the vertical upright column axis X when the resistance of the slip clutch arrangements is overcome.

As shown in FIGS. 3 and 6 a horizontally extending support pipe 13 is rigidly connected to the conical brake piston 10. The support pipe 13 has conically tapering ends 15 which reach into respectively shaped hollow conical recesses in brake bushings 36 secured to the surfaces of supporting sectional members 34 which surfaces face each other.

A pull rod 22 extends axially through the support pipe 13. A locking member 23 is located at one end of the pull rod 22 and rests against the leg 35 of the supporting sectional member 34. The locking member 23 is tiltable about a journal bolt 23' so that the locking member 23 may extend in the direction of the rod 22 for inserting the rod 22 from one end through the support pipe 13. When the rod 22 extends entirely through the pipe 13, the locking member 23 is tilted into the position shown in FIG. 3 whereby withdrawal of the rod 22 with from the pipe 13 is prevented. Set screws 40 may extend through the locking member 23 to bear against the leg 35 when the locking member 23 is in the locking position shown in FIG. 3. Thus, it is possible to arrange the cocking lever 14 selectively on the left side or on the right side of the structure. An eccentric member 25, forming part of the actuating lever 14, is rotatably secured by means of a journal bolt 26 at the other end of the pull rod 22. The eccentric member 25 is effective for cooperation with a spacer member 24 which rests against the outer surface of the leg 35 of the support sectional member 34.

As long as no excessive load or stress is applied to the board 3, the brake pressure produced by the eccentric member 25 prevents a tilting of the drawing board 3 about the support pipe 13. The flexible leg 35 of the support sectional member 34 bends slightly intermediate the clamping position and the non-clamping position. Said flexible leg 35 extends approximately at a right angle relative to the drawing board 3. The spring flexible leg 35 of the support sectional members 34 tends to pull the two brake bushings 36 with their conical recesses into their position in which they do not provide a brake clamping action when the eccentric member 25 is released.

As shown in FIG. 1, a piston cylinder arrangement 29 is located inside the hollow column 4. The piston cylinder arrangement 29 rests on the pedestal 2 to which the outer upright column 1 is secured, for example, by a bushing 2'. The piston 30 of the piston cylinder arrangement 29 is spring supported and operatively connected to the support member 11 with its conical recess. Since the latter is connected through the conical bearing member 10 to the board 3, which in turn is also connected to the inner hollow column 4, the piston cylinder arrangement 29, 30 provides a support also for the inner column in the manner of a gas spring. Thus, the gas spring support of the just described components provides the load relief required for an effortless elevational adjustment of the drafting board 3. The load relief could be achieved by other well known means not necessarily of the gas spring type as just described. A disk spring element 31, for example of the Belleville type, serves as an end stop for limiting the stroke of the drawing board 3 in the downward, lowered direction.

In operation, the above described brake plates 9 secure the inner hollow column 4 against an elevational displacement except when the vertical force applied to the board 3 exceeds the frictional force between the brake plates 9 and the hollow tube 4. The clamping disk spring element 12 and the clamping screw 21 secure the board 3 against rotation about the vertical axis X--X, except when the respective forces applied to the board 3 exceed the force determined by the disk spring element 12 and the friction between the conical member 10 and the conical surface of the recess in the support member 11. The third braking action is accomplished by the friction between the tapering ends 15 of the support pipe 13 in the conical recesses of the brake bushings 36 in cooperation with the eccentric member 25. This third braking action prevents a tilting of the board 3 about the horizontal axis of the support pipe 13. Here again, a slippage is provided when the applied force exceeds the braking force.

Although the invention has been described with reference to specific example embodiments, it is to be understood, that it is intended to cover all modifications and equivalents within the scope of the appended claims.