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How to Calculate a Railroad Curve

The typical model railroad will feature at least one train that can run on a loop, and this means putting in curves or bends. Calculating curves is partly a matter of knowing what the minimal curves are for the scale you are using. If the curve is too tight a train can look cluttered, run poorly or derail. Manufactured curves in segments can solve the problem, but if you are using flexible track or laying your own rails, it is important to learn how to mark your base properly before laying in the road bed.

Things You'll Need

Pencil
Measuring tape
Tack or nail
String

Instructions

- 1
  Determine the minimum curve for the scale of railroad you are building. The conventional minimum radius is 24 inches for HO scale and 9 inches for N scale.
- 2
  Determine the point where you want your train to begin its curve; mark that spot on your base with a pencil. This will represent the inner part of the curve and mark the rail bed edge, not the center of the track.
- 3
  Measure out the appropriate radial distance and mark that point with a pencil to create the center point. For example, an HO scale center point would be 24 in. from your first mark.
- 4
  Press a tack or drive a nail into the center point.
- 5
  Tie a string to the nail or tack.
- 6
  Stretch the string to the first mark and tie your pencil to the loose end of the string so that the pencil point rests on the first mark.
- 7
  Swing the pencil in a circle out from the center point with the string taut at all times to create the inner curve line of the track.
- 8
  Lay your track bed along the curve mark.

Model Railroads