14 
CARLO TROMBETTI 
This table (figs. 12 and 13) consist of a frame holding the drawing plane 32 
(size 200 X 150 sq. cm) and of two rails 1 and 2, on which beam 3 slides (movement 
X). Along the beam runs carriage 4 (movement Y) with pencil-holder 5. As move 
ments to beam 3 and carriage 4 are trasmitted by synchro-receivers (as we shall 
see), it is very easy to substitute movement Z to movement X or movement Y, in 5- 
order to pass from horizontal to vertical plotting. £ 
The frame stands on legs 6, 7, 8, 9, provided with leveling screws (to allow 
the table leveling) and on the two sides parallel to the beam it has springs 10, 11, 
...21 (allowing the drawing sheet to be fixed) ; the springs can be operated by means 
of levers situated at their base. 
The aforementioned rails 1 and 2, set at the two sides of the table, are held 
each by two arms. The rails hold two punched tapes 22 and 23 (22 is clearly to 
be seen in fig. 14) which, as we shall see, give rail 3 movement X : they are fixed 
by springs at their end. Therefore the two tapes do not move and the beam move 
ment is obtained by means of pulleys 24 and 25 (one for each tape), visible in fig. 
15, provided with balls in their end part to mesh with the tape holes. The two 
pulleys are rigidly connected with shaft 26, passing within the beam. 
Along the beam movement Y is transmitted to carriage 4, holding the pencil, 
by means of punched tape 27 (fig. 16), forming a closed loop. This tape therefore 
moves (contrary to what tapes 22 and 23 do) by means of pulleys 28 and 29, 
and they too are provided with balls. Pulley 28 is visible in fig. 15, whilst 29 is at 
the other end of beam 3. 
The pencil is lowered by electro-magnet 30 held by the carriage (fig. 17), and 
its descent is slowed up by pneumatic brake 31. To obtain a clear marking of,points, 
the pencil is rotated by a small motor. In the pencil place one can insert a mi 
croscope holding a circular reference marking, used to collimate the known points 
on the map for the scaling of the model. The microscope is provided with a cali 
brated distance tube to focus the object. 
Box 33 (which is shown closed in fig. 14 and opened from above and from 
one side in fig. 18) contains the slow and fast synchro-receivers 34 and 35 (for X), 
36 and 37 (for Y) and speed-variators 38 and 39 (for X and Y respectively) whose 
function we have already explained. 
The said box further contains all wheelworks connecting the synchro-receivers 
and the speed-variator with pulleys 24 and 25 (A) and 28 and 29 (Y). The diagram 
of fig. 19 refers to movement X and that of fig. 20 to movement Y. 
The first diagram clearly shows that one turn of the slow-synchro-receiver 
rotor 35 corresponds to 1/75 turns of the fast-synchro rotor 34 and to 40 turns of 
motor 38. One should however remember that it actually is the bipahse motor 38 that 
causes the two synchros to rotate. The same axis that connects the fast-synchro to 
the motor rotates wheels F and D which bring about the 1/2 or 1/4 reductions to 
gearwheel C, according to whether they mesh with wheels G and E respectively. 
The further connection with pulley 24 may be changed in ratio by changing the two 
wheels B and C (visible in fig. 18) so as to attain a certain ratio in movements 
between table and instrument. For ratios between 8 : 1 and 1 : 1 (amplification) 
wheel F must mesh with wheel G at the same time using suitable wheels B and C ;