. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . nd tabular values assume that thetwo switch points (at B and D) are directly opposite. Thiswould always mean that the straight rail {BF) is somewhatshorter than the curved rail from D to F. In the maximum casethe difference is less than 4 inches. Therefore, assuming thatrails are obtainable at even-foot lengths down to 27 feet, or24 feet for a No. 4 frog switch, the system of practical leads neverrequires more than o
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . nd tabular values assume that thetwo switch points (at B and D) are directly opposite. Thiswould always mean that the straight rail {BF) is somewhatshorter than the curved rail from D to F. In the maximum casethe difference is less than 4 inches. Therefore, assuming thatrails are obtainable at even-foot lengths down to 27 feet, or24 feet for a No. 4 frog switch, the system of practical leads neverrequires more than one rail cutting. But even this is some-times avoided by using for the straight-rail closure the samenumber and lengths of uncut rails as are specified for the closureof the curved part. The chief effect of this is that the point ofthe switch-rail will be located a few inches below its normal posi-tion at B and that the gauge at the switch-point will be slightlywidened when the switch is open. This effect is possibly anadvantage rather than a disadvantage. 306. Design for a turnout from the OUTER side of a curvedtrack. Fig, 144 is a diagram of what the construction would be. if the switch-rails were circular throughout. Before the inven-tion of point switches and when stub switches were in universaluse, the lead-rails were considered to be circular, both for straightand for curved main track. If Eqs. 70 and 75 and the corre-sponding Eqs. 77 to 80 are solved for any given frog, it is foundthat the lead, when using straight switch-rails and straight frog-rails, is considerably less than when using circular lead-railsthroughout; also the curvature is considerably sharper. Butstub-rail switches are obsolete and the mathematical solutionsused for them cannot be utilized, even approximately, for pointswitches. If such a diagram as Fig. 144 is Worked out in detail,as has been done in previous editions, it is found that 348 EAILROAD CONSTRUCTION. § 307. (a) the lead (BF) is almost iden
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