track turns

[Anonymous]

I'm just starting in model railroading and i was wondering how sarp you can make a turn? The scale i'm going to use is HO and the track i'm goig to be using is the flex track. please write back thanks.

[cwclark]

If you are using GP engines (two wheels per truck) you can go as sharp as 15"radius..If you use SD engines or rolling stock with three or more axles per truck then don't go any less than 18" radius...24" and greater is the minimum desired radius...Too sharp of a radius and the train begins to look like a toy train going around the track. not to mention it can bind the trucks on the bigger engines and rolling stock and jump the train off the tracks...Here is a simple way to make your radius...Get a board about 36"-38" long (a small board like a 1/2" x 3/4") Drill a hole in it about 1/2 " from the end of the board...at the hole you just drilled, take a measuring tape and measure out how much radius you want from the hole to the opposite end of the board...i.e....15"....18"....24"....30"...ect....At the measurement , drill another hole...now take a nail and drive it thru the first hole and into the center of the plywood in line but at the opposite end where you want your curve to start... Take a pencil and stick it into the measured hole (the second hole you drilled) at the other end of the board...now...with a circular, sweeping motion, mark the plywood with the pencil in the hole letting the hole in the board be your guide...This pencil mark looking like a semi circle when you are done is the center of the track radius curve you desire...in other words..the center of the track ties will now line up and curve on the circular pencil mark on the layout plywood.

[DSchmitt]

In HO the "traditional" standard minimum is 18" because it fits on a 4 x 8 sheet of plywood most people have traditionally started with. It works for small steam locos 1st and some 2nd generation diesel locos, switch engines, and 40' cars (maybe a few 50's in the mix).. 60' "Shorty" passenger models were common on layouts in the past. There are prototype 60' cars but most of the "shorty" models represented 80' cars.

A Jetrock says in another thread industrial track can be as little as 12" radius.

Our model curves are very tight by prototype standards. Even a large auditorium would not be enough space to model most areas of the prototype to scale.

In general with curves bigger is better, but you should refer to NMRA standards for guidance. http://www.nmra.org/

[Pennsy58]

Through my own experiences, if you and going to run any of the bigger steam locos or long diesels, like sd-80's or Ac4400's dont make radius tighter than around 22" . The front wheels on steamers tend to jump. With the diesels it depends on the mfg. Athearn's with six wheel trucks tend to have truck turning restrictions by design. Without modifying frames etc keep the radius wider if you can. Of course in yards, where you only run switchers etc. the radius can be alot tighter without problems as previously mentioned.
If you absolutely cant make the radius wide, you might have luck if you run the engines around the turns at low speeds. Hit or miss though.
Regardless of the radius when laying the flex track be careful on lining up joints. If the transition from one section of track to the next is not in radius the engines may jump. I have a piece of plastic that fits between the rails and is cut at a given radius to ensure smooth transition to the next section. Tack the track down good or glue it as it will pull out of radius over time if not. Good luck...