Digging for information continues, and I have had my head buried in many old documents of late, a year’s worth of newspapers in the last three weeks actually, and that will continue for some time.

A few weeks back, at Terry Smith’s prompting, I dug out my copy of the 1888 Scientific America article on the B&SR and referenced a change in my layout design with respect to superelevation of the rails. At the same time I located a later article pertaining to the use of narrow gauge railroads on the front lines during war time. The B&SR was once again referenced.

Like the first (1888 Sci Am), the 1920 Proceedings of the American Society of Civil Engineers article references tight radii, at least per standard gauge standards. Scientific America mentions a radius of 20 degrees and the ASCE article states, on page 664, a radius of 36 degrees was in use on the alignment, in addition to the 20 degree, as well as an average speed of greater than 20 MPH.

The 36 degree curvatures has not, to date, matched any markings on the Valuation maps or the Harrison surveys, so I am thinking that this may have been the radius of the curve (or curves) into the Forest Mills facility. I am not sure if this spur constitutes “the alignment,” as the author states, if such references the main line only. The Harrison survey includes radii of less than 20 degrees, including a 23 degree radius as part of the Y compound curvature departing Bridgton yard and 25 degrees in the proposed village yard.

Looking at the Valuation map V2-1 and map obtained from the Registry of Deeds, the radius of the ROW preceding the Forest Mills spur is about 14.5 degrees and, if the map is even close to being accurate, the radius departing the main line is sharp. Quite frankly, it looks tighter than 36 degrees, however I have not pulled out the drafting equipment yet to approximate the radius.

For those still pondering the question of how tight of a radius is OK for a 2-footer, the following real world examples may help, with approximate scale radii, keeping in mind that the tightest verified radius on the main line was 23 degrees:

  • 16 deg = 358 ft = 89″ (O) = 49″ (HO)
  • 20 deg = 286 ft = 72″ (O) = 40″ (HO)
  • 23 deg = 249 ft = 62″ (O) = 34″ (HO)
  • 25 deg = 229 ft = 57″ (O) = 32″ (HO)
  • 36 deg = 159 ft = 40″ (O) = 22″ (HO)

There is anecdotal information that locomotive #7 had to back into the Harrison corn shop spur due to the tightness of the curvature. Whatever radii you choose for your line, make sure you don’t have to run Billerica and Bedford cab-forward, unless that’s your preferred style.