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But what about a gage of 36.5”? Three-foot-gage was very common, and obviously a whole number. In railroad building, there is always an advantage in having a gage that is common to other railroads, if not for interchange, at least for the probability of obtaining used equipment in the same gage. So, if you are building so close to the extremely common 36”, why would you add .5” and thus eliminate the availability of probably any used equipment? Certainly .5” would not make any practical difference in hauling capacity.
There is an assumption that 36" = 36" +- 0" in your statement. I made the same error for many years. The tolerenece might be say +-2.5% which would mean a window of 1.8" or a gauge range of 35.1" to 36.9" as acceptable for a NOMINAL 36" gauge. Without tolerences, nothing can be maufacturable AND interchangeable. This is going back to blacksmithing each item individually. This goes for electronics, metal working, or anything else.
"The first full-scale working railway steam locomotive was built by Richard Trevithick," [
en.wikipedia.org]
The story goes that he built the first demonstration locomotive to 4' 8" gauge. He had troubles keeping it on the track so he widdened the gauge by 1/2" and the derailments went away.
That is why PRR's 4'9" gauge was just as much Standard Gauge as the 4' 8.5" - it is within the machining tolerence. Now then, the PRR had its rolling stock built to 56.5" but the track gauge was 57". Assuming that the track gauge and the rolling stock gauge is the same is usually correct but not always.
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It is a natural assumption that for any railroad operation, track gage and equipment gage are the same. There needs to be some free play between the fit of the wheel flanges to the track, but this is typically accomplished in the profile of the flanges and the location of the wheel gage line in relation to that profile.
When specifying gauge for rolling stock, you specify track gauge. The flange gauge is calculated from there.
HO gauge (for instance) is the HO track gauge. Wheelsets for HO gauge (flange to flange) are narrower than the track gauge.
On a practical tangent, there was a radar speed indicator manufacturer near where I worked. They tested some of the devices there and displayed the radar reading of the car driving by to the driver.
One car I owned had a speedometer reeding of almost exactly the radar reeding. One car I owned read 10% high - if the reading said 45MPH, the radar said 50 MPH. The other car I owned read 8% low. If the reading on the speedometer was 45MPH, the radar said 41MPH.
My surveying teacher in college said that the exact distance between two points was the average of an infinite number of measurements. Anything else was an approximation - in otherwords there was an error - the real question was is the tolerance small enough?
FWIW
Doug vV
Edited 2 time(s). Last edit at 11/25/2015 06:59AM by dougvv.
