229
We close the vacuum frame and the exposure can be made. The
punch holes are oblong (6x4 mm) and the studs in the glass plate
are circular (4 mm diam.). Consequently, small differences in dimen
sional stability of the sheets will be adjusted automatically in the
best way, because the space between the stud and the outer edges
of the punch hole permits small displacement with respect to the
fixed position of the studs (see fig. 4).
Fig. 4. The oblong punch hole with the circular stud (28).
The four little studs on the glass plate are not placed symmetri
cally with regard to the centre of a map sheet. So it is impossible
to make a mistake by laying the sheet in left-reading position on
the glass plate when we want the right-reading position.
On the other hand one uses a glass plate with studs in left-reading
position when a face-down exposure is wanted.
Fig. 5 shows an image of the cylinder with plunger and some
other details as pointed out in the legend of this figure.
We used thick steel upper- and base-plates, resp. and 2J cm
to prevent bending of the plates. Otherwise the distances between
the four punch holes will not remain constant. The maximum bend
ing of the two plates does not exceed 0.2 mm. The resulting alter
ation in the distances between the punch holes is completely
negligible.
The heavy, very well flattened plates ensure also a good punch
alignment which is essential for a close register of map components
and also for a long life of the punches.
The weight of the upper plate is 88 kg and the loading for each
cylinder with plunger is 23,3 kg.
The diameter of a plunger is 6 cm, and the air-pressure must be
in total atm.
...At
