Templot Club Archive 2007-2020
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posted: 16 Jul 2007 17:14 from: Martin Wynne
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Dear all, There was a question on the ldsig Yahoo group about how to set out a curve by hand, assuming the usual trammel bar (beam-compass) method can't be used. My answer may be of interest (I used inch figures because ldsig is a USA-based group -- it's much easier working in mm): There isn't nearly enough space between the basement wall and the track to use a 77-inch jig. ..... Is there a method available to calculate the curve's exact location on my benchwork?The easy answer is to use a program to print out curve templates. See for example Templot. If you prefer to set it out by hand, here's a method taken from "British Railway Track", the handbook of the UK Permanent Way Institution: set_out_curve.png  ©PWI(Using suitable rulers and a pencil of course for the model, using string lines and pegs on the baseboard is going a bit far!  )You first need to use your calculator to find a suitable chord length and versine for your radius. For a 77" radius, suitable figures would be chord length C = 10.3/4" versine V = 3/16" (TP in the diagram is then half of C = 5.3/8") The formulae for other sizes are: Versine = half of chord length, square it, divide by radius, divide by 2. Or: Chord length = versine multiplied by radius multiplied by 2, take square root, multiply by 2. These formulae are approximate, but close enough for railway work (where the versine and chord are always small in relation to the radius). regards, Martin. |
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