[quote="kleaverjr"]... The prototype uses degrees to calculate the radius of their curves somehow (I still don't understand that myself how that works!) ...
Ken, et al,
Actually, "radius" is mostly a modelling thing. Most twelve-inch-to-the-foot railroads aren't drawn up using turn radii because (a) the radius changes as the track eases into the turn (easements) and (b) the "center" of the hypothetical circle would be too far away, and probably too inaccessible to do any kind of arc scribing. Imagine trying to pound a stake into solid rock 1000 feet into a mountain to get that 1000 foot radius turn in a narrow gorge.
What really happened was that surveyors would measure curves in "degrees per chain." A chain is a surveyor's tool -- quite literally a chain 66 feet long (ever wonder why an acre is the size it is? 2 chains x 5 chains = 1 acre) and the surveyor would have his assistant pull the chain tight to 66 feet "straight ahead." Looking through his transit (a small scope with a compass beneath it,) he would then have the assistant go a set number of degrees to the left or right of the point and drive a stake. Curves along the Right of Way might start out at some fraction of degree per chain, and get progressively tighter, say to two or three degrees per chain, and then ease back out to straight on the other end of the turn. The advantage here is that if you knew you had to make 30 degrees of turn, you could spread that out over a certain number of chains without needing much more than the transit and chain.
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