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Full text of "Modern Mechanical Engineering Vol-I"



such as thickness, &c., but to make the drawings show similar views in
similar parts of the drawings, and to make all the drawings of exactly the
same size and style. For many classes of work it will be found very good
practice to take a sheet of double elephant drawing-paper and divide it in
four equal parts by drawing both vertical and horizontal centre lines. In
each quarter thus made one standard may be put, complete in all its details.
This sheet after being traced will be photographed, so that four standards
will be on one sheet. After photographing, each standard may be cut up
into a sheet by itself, and perhaps a dozen or twenty of them bound in one
book, the covers of which may be formed of stiff drawing-paper, stitched
with strong twine.

An example will make the above procedure clear.    Most drawing offices
have to use steam or water valves in some part of the work.    These
either globe pattern or L pattern, high pressure or low pressure, and
of cast iron or gun-metal.   It is obvious here that six standard books will
made up, showing valves, say, from i|-in. bore to ic-in. bore or thefeabojut,
rising in the smaller sizes by J in. each time, and from 3 in. to 7 in. bj^ An
and thereafter by i in.   The outer cover would be marked, for instange


220 lb. per square inch



For standards such as the above, which are in everyday use by a number ^N *'
of men in the office, it is usual to have several sets of each standard, which
will be kept in the safe and given out on the requisition of a section leader.
On no account should the tracings leave the safe, nor indeed any other
tracings, unless for photographic work or for modification, for the loss or
misplacement of a tracing is a serious matter entailing considerable work
and annoyance in having to be remade, as such may perhaps cause very
serious inconvenience at a very busy time, say when a telegraphic request
is received for a photograph of some important part which has to be repaired
or replaced immediately.

Circulation of Drawings.  It is important to have a fixed routine
for the circulation of drawings. Each department may have only a small
part to do on any one drawing, but it is general and even advisable to issue
the complete finished drawing in each case. It is general practice to do so,
because it saves the preparation of several drawings  an important point
both as regards time saved and the reduction of error, for the preparation
of each fresh sketch or order-form involves risk of error, particularly as
such subsidiary sketches would be left for juniors to make. Not only so,
butjt is a false notion of efficiency to show a craftsman only the little por-
tion of a job he must do. A better job is done because of the knowledge
he has of the whole and its general purpose, and he may be in the position
to save some part of the process by his practical knowledge when he knows