I previously used only flex track for my curves. Now I plan to construct a double track mainline with Atlas snap track. There is only one problem. If my inside curve is 18" radius, what is the proper curvature of the outside curve? I think it might be 22" radius, but I’m not sure. To anyone who might read this, I would be grateful for a response.
TheNarrowGaugeMan
you are right on…the outside track would be 22" radius for a double track. if the inside track is 18".
Thanks for the reply.
TheNarrowGaugeMan
If you are going to go with snap track, 18 and 22 radii are your choices. The problem with that is your mainlines will be farther apart than what would be prototypical. Four inches is 29 feet in the real world. Two inches is closer to prototypical rights of way but with tight curves, you need to allow a little more room. I would try to put the mainlines 2.5 to 3 inches apart depending on the length of your equipment. It will look more prototypical that way. Of course, that would force you to use flex track for one of the curves.
Just out of curiosity, why do you want to use snap-track and not flex track? I realize it’s probably less time consuming and labor intesive than flex-track, but also less flexability(pun intended) than flex-track; this discussion on multiple other threads is why I will be doing my layout with flex-track over cork roadbed. Negative past experience with flex-track?
Jim
Good question there, jbloch; I would have ask it if you hadn’t.
Atlas designed the 22 inch radius snap track because it was the largest radius which can be fitted in the 48 inch dimension of a 4 x 8 sheet of plywood. When tacked down it leaves only about one inch from the edge of the tie strip to the edge of the platform; my model railroad career almost came to a screeching halt in 1963 when I derailed my only piece of motive power - which my income in those heady days of yesteryear would almost certainly have prohibited replacement - at this closest point to the table edge, It almost went over the edge onto the concrete floor of my garage. This experience let mt to reduce the radius at the 48 inch end of my platform to 18 inch radius; I never had that close call again. I currently lay my double track at the end of a 4 X 8 platform with 20 inch and 18.5 inch radius curves - and that is in N-Scale.
My advice is that if the poster insists on using 18 and 22 inch radii for his double track that he go at least to a 54 inch wide platform.
What scale?
Knowing that determines the proper track center distance.
I really wish some people would do a little research before they just post anything off the top of their head. According to Atlas, the answer is a 20 1/4" radius curve. This is in chapter 9 called “Designing Your Own Track Plan” in their book “Atlas Custom Line Layouts for HO scale railroads”. This book is an essential reference for people using Atlas snap track.
It is composed as such:
full 22" curve
half section 18" curve
full 22" curve
full 22" curve
half section 18" curve
full 22" curve
full 22" curve
half section 18" curve
full 22" curve.
To get a separation of 2 1/4" between mains on the straights, use a 1 1/2" straight section between the turnouts of a #6 crossover, and a 1" straight for a crossover made with #4s.
Another way simple way to do this is to 18" curves for both tracks. Put a straight section on the outside curve. For each 90 degree section, the length of the straight should be equal to the separation of the two tracks. That is, a double tracks with the same 2 1/4" separation as above, construct the outside curve as thus:
2 1/4" straight
three full 18" curves
two 2 1/4" straights
three full 18" curves
2 1/4" straight
In my opinion this last option looks a bit boxish, but it does actually provide a greater separation for cars with large overhangs.