50 links per inch chain


Schuyler Larrabee
 

I’ve been thinking about the use of 50 links per
inch chain for the linkage between the brake
cylinders and the rod leading to the end-of-car
brake wheel. I thought I’d do some math.



50 links per inch works out to an individual link
.0.020” long. I took a look at some prototype
drawings I have, from ACF via the St Louis
Merchatile library. Specifically, these drawings
were for the RI Autobox car, the 2016 Shake’n’Take
car. Those drawings depicted the linkage with the
links “relaxed,” that is not under tension, so
therefore the position they would be in with the
brakes released. (Or at least, not engaged by the
brake wheel.)



The main links as drawn in that chain scale out to
be very close to 3” long, 3” at HO scale is
0.034”. 1/.034 = 29.41, round off to 30, so a
chain with 30 links per inch would be accurate to
scale.



Bur there’s more to consider here: at either end
of three links in the middle of that connecting
chain on the RI car, are two longer links, which
scale out as drawn in the drawing I have as being
4½” long. 4½” at HO scale is .052”. 1/.052 =
19.23, round off to 20 links per inch.



The ACF drawings I obtained for the ERIE car, the
2018 Shake’n’Take project, show the chain
stretched taut, and are not informative as to
varying lengths of the links. But a photo of the
prototype car clearly shows not the two links at
the ends of the chain, but one longer link in the
middle of the chain.



On both the RI car and on the ERIE car I modeled,
I did this: For the RI car I use two links of 20
lpi chain at either end of three links of 30 lpi
chain and fastened those longer links to the rod
and clevis. Cutting the link is easily done with
a razor blade, For the ERIE car, I used a single
link of the 20 lpi chain between several links
(three each end as I recall) of 30 lpi chain,
which I fastened to the rod to the end of the car,
and to the brake cylinder’s clevis. .



It appears to me that 50 lpi chain isn’t really
necessary for freight car brake chain.



One other point: scale chain links are typically
round; prototype brake gear chain links are not,
they are oval. Given the limited number of links,
I’ve >>gently<< squeezed the links to get them to
be less round and closer to oval.



After all, if we’re going to go to the effort of
doing what I describe above, why not?



I will post (perhaps not tonight) some images from
the drawings and the image of the ERIE car.

Schuyler





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