3.18.
EQUIPMENT
What equipment do you need to put stringlining into actual practice in the field? To mark off the stations
and measure the ordinates, you need a tape at least 31 feet long, graduated in feet. Any such tape will do,
provided the same tape is used to measure all the stations on a curve. You also need a strong string, 62 feet long
or longer, marked at the 62-foot point. A ruler, graduated in inches and eighths of an inch, is required for
measuring ordinates. One graduated in inches and tenths will do, if a similar rule is used for all lining of a
particular curve. However, in this discussion, all ordinates are expressed in eighths of an inch. You also need a
notebook, a pencil, and a heavy crayon. A pair of wooden blocks, 1 by 1 by 2 inches, known as offset blocks, are
helpful. To mark the distance the track is to be moved, you need wooden stakes, surveyor's tacks, and a ruler or
tape.
3.19.
MARKING OFF STATIONS
The first step in stringlining is to divide the entire curve into 31-foot lengths. This is
known
as marking off the stations. You start at some point on the tangent, marking it with a heavy
crayon on the web of the outside rail, as shown in the sketch. Then you measure 31
feet
toward the curve with the tape and mark this point in the same way. Each of the
points
you mark is known as a station, and you number them consecutively from the first
point to the end of the curve, as shown in the sketch.
Let
us
assume that you marked two stations the first time you stretched the tape;
the
first
is
numbered station 0 or Sta. 0, and the second Sta. 1. Mark their
numbers
on the web at the station marks, and enter them in a column
in
the left margin of your notebook. Now measure 31
feet beyond Sta. 1, and mark and record Sta. 2.
Continue this all around the curve, until you are out
on the other tangent. In practice, it is a good idea to start far enough down the tangent to have 10 or 15 stations
on the tangent, and to have 10 or 15 more beyond the curve on the other tangent. Why? Because the straight
track at the approaches to a curve is likely to be disturbed by the passage of trains around the curve, and its lining
should be checked.
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