Curved Turnouts

[doggeface]

Having no access to computer aided design I sat down to draw out a curved turnout. The outer radius to be 1400 mm and the minor 1200mm. I found the nose angle to be 1:10 and the overall length (to the median parallel track separation distance of 25mm i.e. total separation of 50mm) to be 680 mm.
This gives a need for 1360 run to accomodate a curved crossover (1 LH mating to 1 RH).

I would be very grateful if someone could spare the time to confirm my results.

Best Regards

Peter

[grovenor-2685]

Just measured my curved crossover, which is 1:10 although the radius is a bit tighter than yours, it measures 800 mm toe to toe.
When I have a few more minutes I'll run your numbers through Templot.
Regards
Keith

[grovenor-2685]

Peter,
I think there is something wrong with your frog angle of 1:10
I have run some checks on Templot.
With a main line radius of 1400 and the turnout to the inside of the curve the minimum radius of the turnout road is as follows:
Switch, Crossing, Min.Radius,
B, 1:10, 890mm,
C, 1:10, 1001mm, Length of crossover toe to toe, 50mm track centres is 820mm.
D, 1:10, 982mm,
E, 1:10, 960mm,
C, 1:12, 1025mm,
D, 1:12, 1096mm,
E, 1:12, 1071mm,
D, 1:14, 1116mm,
E, 1:14, 1152mm,
F, 1:14, 1139mm,
D, 1:16, 1116mm,
E, 1:16, 1211mm, Length of crossover toe to toe, 50mm track centres is 1280mm.
F: 1:16, 1197mm,
Note that for each crossing angle there is an optimum switch length, shown in bold, these are called natural turnouts.
To achieve your desired minimum radius of 1200 you have to go for the E16, which is not far from your estimated length for a crossover.
Note this length assumes using an E16 on both turnouts, as the turnout road on the inner track will have a larger radius than the 1350 of the main track you can use shorter switches here and save some length, you can come right down to a B switch (B16 turnout) and save 188mm in the toe to toe length.
Regards
Keith

[doggeface]

Thanks for those numbers Keith - they are very useful. I agree with your remarks regarding the nose angle. Now that I have inked in the design the angle is more evidently 1:16. I can reduce the length overall by bringing the inter track clearance (distance between outer rails) to 30mm which seems to be prototypical. I shall be very glad when these track plans (or more to the point - turnout plans) become readily available!

Peter

[grovenor-2685]

Standard double track spacing is 6ft between outsides of rails which adds up to 4'8.5" +6'0" + 5.5" = 11'2" centre to centre, near enough to 45mm for us.
Reducing the spacing to this figure will save you 5 x 16 = 80mm. This should still leave enough passing clearance with your radii but if you are using vehicles with large overhangs, eg big pacifics or 70ft coaches it would be sensible to check.
Regards
Keith