Dennis Storzek <destorzek@...>
--- In STMFC@..., "Tony Higgins" <earthman92853@...> wrote:
The spring plank is/was a channel section that runs between the bottom
of the side frames, each end located directly under the spring seats.
These were sometimes made from structural channel, sometimes from a
steel pressing, and were originally a wooden plank, thus the name.
In the old time swing motion trucks this plank actually hung free of
the truck frame and held the springs the bolster was supported by.
When swing motion freightcar trucks fell out of favor (too much
complexity, too many wear points) the spring plank was retained with
so called rigid frame trucks, which is what almost all cast sideframe
freight trucks are. The purpose for retaining the spring plank was to
keep the bottoms of the sideframes in line. However, improvements to
the form and fit of the gibs that hold the bolster in the sideframes
made the spring plank unnecessary, and the use was dropped shortly
before WWII again to reduce weight and complexity.
Most one piece model trucks don't attempt to model the spring plank
between the sideframes, due to the complexity it would cause to the
part. Typically, only the ends are modeled where they show under the
springs on the outside of the sideframe; both the Accurail
"Bettendorf" and Andrews trucks have this detail. One could, of
course, fit the spring plank between the sideframes, but then getting
to the truck screw would be problematic.