Its been nearly 40 years since I last purchased track, and I seem to have forgotten so much. My dumb question is what does the number on turnouts stand for, and what is the difference between a #8 and a #6 ? I am guessing it is the radius but I want to be sure. Also on a double main line how far apart should the track be separated measuring from center to center of the rails ?
Thank You in advance
Ron
The number is a measure of how rapidly the two paths diverge. Smaller numbers are faster divergence, and thus a shorter turnout. It’s better to think of it this way, rather than “radius.” If you look at numbered turnouts, you’ll see that the divergent tracks are generally not curving much at all, but almost straight as they come out.
Atlas makes “snap-switches” which actually use curved tracks as divergent paths. These work too, but you’ll notice that they are not “numbered” like, for example, the Atlas Customline turnouts. I think the snap-switches work out to about a number 4 1/2 turnout.
While a #6 turnout looks luxurious on a model railroad, the prototypes actually use much longer turnouts in general.
Ron,
It is not a dumb question. It is just a very repetitive one, perhaps one of the most asked questions about track.
A turnout’s number expresses how much it will cause a train to diverge when it is thrown. The number is calculated by taking the number of units of forward travel for one unit of divergence. For example, if after traveling eight inches from the point of divergence the train has diverged one inch, then you have crossed a #8 turnout. The smaller the number of the turnout, the tighter the radius of the turnout’s curve. So, for example, a #6 turnout is a tighter radius curve than a #8 turnout and a #6 turnout diverges faster than a #8 turnout because of the tighter radius of the curve.
On a double mailine in HO scale, the track separation is typically 2 inches on center on the straight line portion of track. On curves, the separation is usually between 2 1/4 inches and 2 1/2 inches.
Rich
As noted the number refers to how much distance it takes the diverging leg to separate one unit from the straight leg. That is a #8 diverges 1" for each 8" of length. Curved turnouts like Atlas snap switch are not numbered because the diverging route is curved thus constantly increasing the rate of divergence. They are instead best described by radius, the Atlas snap switch being 18" radius.
Within the a normal turnout there is a radius in the closure rail that affects stiff wheel base equipment such as steam locomotives. This is 15" for a #4 turnout. Because of this many manufactures don’t make a true #4. For example Atlas HO #4’s are really #4 1/2’s.
Here’s the NMRA web page for turnout dimensions for HO http://www.nmra.org/standards/sandrp/rp12_3.html Other scales have their own page on the website
Enjoy
Paul