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Full text of "Modern Mechanical Engineering Vol-I"

26                   DRAWING-OFFICE   ORGANIZATION
and if new prints are sent out in place of any recalled, a red chalk-mark
should be added to draw the attention of the shop foreman to the modification.
Time-book.—Each draughtsman keeps a time-book in which he
should enter up the time he spends per day on each job. Generally the
complete job number will be held sufficient, as few offices do more than
make an overall calculation of time spent on any individual contract.
Record of Alterations.—An experienced section leader will keep a
list of the alterations made during the course of the job, with a note of the
authority from whom he received instructions to make the changes. This
practice not only keeps him right in the case of disputes later on, but is
necessary, as a set of correct tracings of the job as finished may be required.
In this set of finished tracings alterations made outside the office, sometimes
without office sanction and at the request of a surveyor or inspector, are
expected to be incorporated. This will mean that a few journeys to the
ship or site may be necessary and a note of these alterations taken. The
working drawings should be altered accordingly in red.
Key Diagram.—In large arrangement work it is usual for the section
leader or his most experienced man to make outline key arrangements, and
sometimes what may be called a connection diagram. This diagram would
show in end vertical column the sources of power, and on top horizontal
column the auxiliaries to be driven. In the square common to each put
a circle with the bore of the connection. By this means a complete tabular
statement of all connections can be given. Such a diagram is the key by
which the section leader will check subsidiary drawings and orders.
Such a key diagram is shown herewith, dealing with auxiliary connections
for a large marine-engine installation. It is quite possible that the same
item shall appear on upper horizontal as well as on left-hand vertical column
heading. To show how it is worked, take the item " Steering Engine " in
vertical column. We find a circle with the size 2\ in. under the heading
" Reduced Steam ". This means that steam to steering engine is not taken
direct from boiler, but from a reducing valve. Of course the lead to the
reducing valve itself will probably be taken direct from the boilers, but this
does not affect the key diagram. Similarly, it will be evident that exhaust
steam from steering engines must be arranged by a suitable arrangement of
valves and connecting pieces to go either to main or auxiliary condensers,
feed heater, atmosphere, or L. P. turbine. This connection diagram is very
often translated with a key sketch actually showing the place of main engines,
boilers, and auxiliaries, and lines drawn connecting them. This is not really
necessary, as the connection diagram shown should give all that is necessary,
but the diagrammatic sketch makes it clear to juniors. It is understood that,
in column marked " Makers ", the name of the makers of any auxiliary
machinery should be inserted, simply as a convenience to the section leader.
It is usual in large contracts to send such key drawings and diagrams,
as well as the principal drawings, to the owners for approval. It is highly
desirable to get this approval at an early date, so that material can be ordered
early The usual plan is to send two thin prints of each, one of which will