I have a 90 degree curve that has a 26" radius. What radius should I use to add a parallel track on the outside of the existing curve? Scale is HO and max car length is 80’. Largest loco is a Pacific.
Thanks,
Use a 28 1/2" for the outer track. This will give you 2 1/2" track centers that will allow clearance for even the largerst pilot/ truck overhang. Of coarse you could check w/ a mock up and may be able to get it down to 28 1/4" (2 1/4" centers). Since this turn separation is so great, you can bring the track center back to 1 3/4 or 2" by adjustment of the easments. Straight track does look much better at that closer spacing.
The NMRA suggestions for track-to-track spacing are often a good starting point. 2 1/2" separation would be safe, but 2 1/4" is likely sufficient for the rolling stock you are describing.
The largest equipment you have today may not be the largest equipment you ever wish to run, of course …
Bruce, I don’t have a lot of time or experience, but so far I can say I have learned to plan for future contingencies. In fact, for about four years now, when people ask for advice about some of the basics, I always include an appeal for the asker to think ahead about what may be coming down the…uh…pike, yeah, that’ll do…that may mean modifications and expense they’d rather do without.
I had good results with the clearances I had built into my steep terraced concentric track curves at each end of my layout. Leaving aside all the warnings about that arrangement, all my various engines and cars were clear and worked fine with the rock cuts ‘right there’. Then, I purchased the Rivarossi Allegheny. Of all things that tripped me up, it was the overflow downspout on the engineer’s side. That thing sticks way out from the truck under the cab, so far that on those end curves, I could hear loud chattering. How I didn’t break off that plastic pipe and flare I’ll never know, but it got me carving right away. And rather than mar that superior engine with all its fine details, I had to go back to scenery alteration.
So, if any of that follows your question, I would say to err on the side of caution and generosity…add the 1/4". Better yet, mock it up and get a good look. You would want a full 3/8" separation between the middle of a passenger car on the outside curve and the cab or pilot overhang on a large steamer.
-Crandell
I am with you on this Crandell. I made the mistake once of not planning ahead and won’t do it again. It’s just better to me to err on the side of too much spacing than too little. Having to go back and rework things is a pain in the rear.
OK, I got that. Now how about when the two curved tracks become side by side in a straight line. eg what is the minimum spacing in a straight line? I could leave the spacing at 2 1/2" but that would waste real estate unless there is a good reason to leave it that spacing.
Two inch “center to center” spacing on straight parallel tracks is usually adequate. Bob Hahn
Well, it depends. Where is the track and what is its purpose? Out on the main, away from turnouts, you could do as Bob suggests. If, on the other hand, you anticipate having to reach between the tracks with fingers to clamp onto cars for some purpose, especially reasonably often, say two or three times a session, you would want to leave room for your fingers. A siding is going to need only 2" centres, probably, but a yard track is likely to be much easier to use with some additional space between it and the next one.
-Crandell
On my two track main I keep the distance consistent at 2-1/2" strictly for visual purposes. I can ever recall seeing a main narrow down after coming out of a curve but thats just my experience it’s strictly for aesthetics