PROVIDIUNAL DI DUITIVATION Improvements in or relating to Adjustable Drawing Tables.
Year: 1898

page_text: Date of Application, 28th May, 1898
PROVIDIUNAL DI DUITIVATION
Improvements in or relating to Adjustable Drawing Tables.
I, CARL ALBERT HIRTH, of No. 34, Kanzleistrasse Stuttgart, in the German
Empire, Civil Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to an adjustable drawing table with easily removable
straight-edge.
My invention is essentially characterized by the arrangement of the drawing
table to be adjustable at any desired height and inclination by being supported at
cne side by means of a parallelogram or other rectangular mechanism so that the
table can be adjusted at any desired height and at any angle; straight edge being
suspended at both sides by straps or the like for the purpose of being easily lifted
from the drawing board; said straps running in helical grooves over rollers of
exactly equal diameter, and rigidly attached together; for the purpose of securing
an exact parallel guiding of the said straight edge.
The improved drawing table is adjustable in any desired position or inclination,
because it is attached to one side of a parallelogram mechanism. The latter can
also if desired be replaced by any kind of unequal sided quadrangular guide be-
cause by aid of such a mechanism the same result can be obtained.
The drawing bar in connection with the drawing table can easily be raised
from the drawing surface, being freely suspended at both ends by straps or the
like. The exactly parallel guidance of the said bar is attained by winding the
straps or the like upon rollers of exactly the same diameter, which rollers are
rigidly connected together, and provided with helical grooves for the reception of
the straps so that these will be wound up or down exactly equally.
My machine is preferably constructed as follows;-
Upon the base thereof are fixed two uprights in which a shaft is revolubly sup-
ported. Upon the said shaft are secured two levers connected by a cross piece.
The other ends of the said levers are connected to the bearings placed upon the
frame which holds the drawing table. Along with the aforesaid levers there are
arranged upon the shaft two other levers which are revoluble, and which are also
connected together by means of a cross piece. The hubs of the levers last men-
tioned are divided and provided with bored and threaded projections by means of
which the said hubs, and consequently also the levers belonging thereto, can be
clamped rigidly upon the shaft by means of set screws as soon as the drawing
board has been brought into the desired position. Through the ends of the bear-
ing of the said levers there passes a shaft upon which further levers are revolubly
secured connected by another cross piece. The other ends of the said levers attach
loosely to a bar passing through bearings attached to the bed plate. The last
mentioned bearings are connected together by means of two bars to which the
bed plate for the drawing board is attached. Upon a shaft there is also provided
a lever serving as a counterbalance. The above mentioned parts, together with
the bed plate, constitute together the parallelogram mechanism, and it will be

page_text: is ako secured a.lever. q with.counterweight. q! which balances the drawing board.
The levers de y and table. form together, as may be seen from the drawing, the
parallelogram support, and it is obvious that the same adjustability can. be ob-
tained it instead of a parallelogram any desired unequal four-sided figure be
selected as the guiding device.
In Figure 2 the drawing board is represented in an almost perpendicular position.
If it be desired to bring the same into the position shewn in dotted lines in the
drawing it is only necessary to raise the table carrying the said drawingboard m.
The apparatus is counterbalanced in any position, as already stated by means of
the counterweight q
If it be desired to place the drawing board in a more horizontal position, as
shewn in Figure 3 for instance, the screwbolts e are released so that the levers e
can move upon the shaft into the desired position, and they are then clamped
in this position by turning the screw bolts e
In this manner the drawingboard may be easily and conveniently arranged at
any desired height and slope.
The second improvement consists in that the cross bar t can be easily raised from,
the surface of the drawing, and that the drawing, board can be removed or replaced
without difficulty. This is attained by making the cross bar quite independently
supported with regard to the drawing board. The preferred arrangement is as
follows:-
of
To the table are fixed two bars and bearings in which latter the pivots
the pulleys, connected rigidly together by means of a tube s, are supported (see
Figure 4). Each of the pulleys consists of a wheel r¹ provided with spiral grooves r
and having a smaller pulley. In the grooves are the cords t attached to
the bar t, serving as a straight-edge for the draughtsman. These cords are secured
to the wheel by means of a hole therein (Figure 4). Upon the smaller
wheel there is coiled a cord z provided with counterweight 21 and adjusted to
the required position of the bar t. This cord is attached to the wheel 2 by fasten-
ing it in the hole r. Two loops attached to the table secure the regular coil
of the cords t¹ upon the wheels r¹. As the bar is freely suspended from the ends
of the cords it can be raised (as shewn dotted in Figure 2) at any time from
the drawing board m, whereby the advantage is attained that during
the drawing if it be desired to move the bar upwards 01' down-
wards the drawings need not be touched thereby. The principal advantage, how-
ever, consists in that in consequence of the independent support of the bar from
that of the drawing board, the latter can be removed or replaced at any time, being
freely detachable from the table without rendering the slightest alteration necessary
in the position of the bar t. The weight of the bar t and of the piece connected
therewith can be balanced by other means than those shewn, such for instance as
by means of springs.
T
Figure 5 shews a device of this kind in which the spirally grooved pulley
is provided with a hub 76. Around this is placed a spring box I which contains
the spiral spring 2, one end of which is secured at 3 to the spring box 1, and the
other end of the said spring is attached at the point 4 to the hub r6. In the
wheel is inserted a pin 5 around which the spring box, together with its hub 6,
is revoluble. Between the periphery 7 of the spring box and the bearing o is
placed a lever disc 8, and the projection 9 is rigidly connected to the hand wheel 10.
The spring box hub ends in a screw pivot 11 upon which is screwed a nut 12.
It will be seen that by turning the hand wheel 10 upon the hub of the spring
box 1 the spring 4 can be stretched more or less, whereby a mutual displacement of
the grooved pulley r, and of the spring box is occasioned. When the spring is
sufficiently stretched, the periphery 7 of the spring box is pressed by means of
the nut against the lever disc 8 of the hearing o, and thereby fixed in position.
In the illustrations the bar is shewn as hanging freely suspended from the
cords, it will, however, be obvious that this can be suspended otherwise, as for
instance by means of oscillating levers; further, this method of supporting the bar