I've posted this question on several other forums and have not gotten any definitive response. Please keep in mind that I am only asking how the length of the LEAD in a switch is determined. Back when they first started building and designing track switches, how did they know how much distance to keep between the point of the frog and the points of the switch. What is the formula to determine that? Perhaps I should be asking someone who actually builds these things, but I don't know how to locate him. Rick
Venturing an answer, seems to me it would be the size of the switch. For a number 6, it would be six times the track guage. For a number 10...ten times the track guage.
Why are you asking? If it is for data to build your own turnouts, one of the best places to start is the NMRA Recommended Practices page: http://www.nmra.org/standards/consist.html#standards This is arranged by scale and by turnout #. You are looking for RPs numbered 12.X Some people who build their own turnouts use longer leads than the NMRA recommendations because of the look or because they feel they operate better. If you are building in place, you may vary the leads as you like. Some templates like the Fast Tracks line allow one to build turnouts at the bench, but I don't think it's possible to vary the lead length. The Fast Tracks are based on the NMRA specs, I believe. http://www.handlaidtrack.com/ I have seen a number of prototype data sheets for turnout construction and each specified a different length for the lead of the same numbered turnout. These differences are slight and often the lead length is given as a minimum. The prototype engineers would often build longer leads as necessary to avoid putting the points in a grade crossing, bridge, or in a spot that interfered with other trackwork. So the length seems to be trial and error or an individual engineering department's preference and may have varied over time. Just as an example, here are lead lengths for a # 6 turnout. PRR (1909) 45' 11 3/4" C&O (1913) 53' 6" nominal; 50' 0" minimum NMRA 43' 5" So the NMRA specs are a bit shorter than either of these two prototype examples, but offer a compromise of functionality and appearance vs. the space required on the layout. Other info sources include a set of generalized prototype (A.R.E.A 1926) dimensions scaled for model use: http://www.prototrains.com/turnout/turnout.html Also, you might want to look at David Honner's useful Excel-based turnout calculator, which can be found a ways down this helpful page: http://www.urbaneagle.com/data/ Another reference is Tony Koester's articles in the Dec 1989 and Nov '98 issues of Model Railroader. Handlaid Code 40 turnouts in N scale were covered in the Sept. '98 MR. Regards, Byron March/April newsletter online http://www.modelrail.us/news
