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(Use AnyRail
to show track/roadbed design.)
You might think it's time to lay track, particularly if you have
a table top layout. But take a look at a real railroad and you'll
notice that the track isn't laid directly on the ground (well some
early and not very successful railroads were built this way, but that's
another story) but on a bed of gravel. This bed of gravel is
called "roadbed" and a model railroad should have this even if built on
a table top.
Many materials have been used for roadbed but today the overwhelming
favorite is
split
cork roadbed. The cork roadbed can be nailed or glued.
On open grid benchwork a sub-roadbed must be used. This is
typically 1x4 lumber or plywood (or other similar material) cut to
shape and installed on the grid structure.
Cork roadbed looks sort of like gravel at least in the smaller scales
and many model railroaders will leave the cork roadbed as
finished. But others will glue loose pieces of material onto the
cork roadbed to better simulate real roadbed. This is done after
the track is laid and is not discussed further here.
To make an accurate representation of a track plan with the roadbed
several methods are possible. One is to make a full size template
and bend the roadbed to fit. Another method is to transfer
control
points off the track plan to the layout. A modification of this
method involves using some type of flexible wood and pinning it to the
roadbed and letting it form a natural curve to serve as a template.
Real railroad curves have easements which uses a gradually increasing
radius between the straight (or tangent) section and the final
curve. This is equivalent to the way a car is driven; you don't
instantaneously go from straight driving to the desired radius of a
turn. Instead the steering wheel is gradually turned from
straight to the desired degree of curvature. This is actually an
easement. Easements can be simulated with sectional track by
using sections of different radius.
References:
http://www.nmra.org/beginner/track.html
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