Curve radius question ?

Model Railroader Layouts and layout building
1

When measuring the radius of a curve are you measuring from the outside rail, inside rail, or center of the rails ?

Thanks.

Ron

2

Center

Smile,
Stein

3

Thanks for the quick response. On center was what I was thinking but I wanted to make sure. My benchwork is only 2’ wide so I am making templates to draw the curves onto the layout.

Ron

4

Templates work. If you have a camera tripod and a yardstick you can use that, too. I drilled a hole in a stick to fit over the mounting screw on my tripod, then drilled holes at various radii along the stick to hold a marker. Pretty simple and quick.

–Randy

5

The ole nail with string works along with a template. Just measure the string and put a pencil on the end of it. Tie it to a nail and use the pencil to draw the curve. Quick and easy.

6

Ron, just don’t forget to allow for easments ( easing your equipment into that radius).

7

I use that system, too, but I use small decorative chain instead of string. String can stretch.

8

When using the method I also start by laying a small piece of roadbed down and measuring to the edge. That measurement is used for the line so that the roadbed can be lined up. To get a 30 radius for the track the line is drawn with about a 29.5.

9

Great idea, Randy!

10

I used curved Atlas code 83 snap track as templates to lay out most of my curves. I bought three different sizes. 15 inch, 18 inch, and 22 inch. I use the 15R for some industries. Anything larger than 22R you can use flextrack and pin it down temporarily. For easements on 18R, I used the 22R.

11

Thanks for the info all. The old pencil on a string wont work, because my benchwork is 2’ x 4’ modules open in the center, but Randy had a great idea using a camera tripod and a yardstick. I have some 1/4" plywood that came as packing material and have been trying to figure out a use for it, (I hate to throw away anything) and thought that it would be great for templates.

Now can anyone tell me how long should my easement into the curves be?

Thanks

Ron

12

An easement is a small offset “to-the-outside” at the end of your curve radius. Easements are actually tangents to the curve. Easements are sometimes hard to describe in words to give you that word-picture.

So, here are (3) past easement curves threads providing answers from just about “any angle” you can think of…

Easement Thread #1 – Easement Thread #2 – Easement Thread #3.

13

Not to make this too complicated but there are also increasing and decreasing radius curves(actually one is also the other, depending on direction) in the real world and on my layout. Understanding the origin of each radius and blending along with the easements make for some real engineering. This concept is particularly useful if you don’t have an exactly symmetrical area to put your curve. I try to map it out on graph paper to a reasonable scale and then scale up for the layout. CAD is nice too. In addition to the many great ideas posted here, I would suggest ribbon rail which is a tool that can be inserted between the rails to help you maintain a radius as you lay the track. Shinohora also makes a wide variety of larger radius curves as I recall.

http://www.walthers.com/exec/search?manu=170&category=Track&split=30

Richard