Newbie question of the day...Curve Radius.

[NewConductor]

Ok, i just can't seem to wrap my mind around this one, but think i'm halfway there, or halfway stupid, take your pick. lol
If i want an 11 inch curve radius, does that mean the inside rails need to be 22 inches apart?

I've read some stuff on curve radius but i've hit a mental block & it just won't gel in my head. Help!!

[n-scale chesapeake & ohio]

it means from the start to the end of half a complete curve it will measure 22 inches in length.

[Desertdweller]

Not really, not if you are talking linear feet.

A radius refers to half a diameter.  The diameter is measured track center to track center of a circle (or half circle) of track of a constant radius.

So: A 180 degree turn of constant 11" radius track will measure 22" track center to track center, measured through a point equal distance from both ends of the curve.

If this is hard to visualize, try this.  Tie a pencil to one end of a piece of string.  Measure 11" from the center of the pencil, and tie a tack to the end opposite the pencil.  You now have a compass with an 11" radius.

If you have a shelf layout 24" wide, measure 1" in from the outside edge.  This is where your track center (the center point between the rails) will fall.  Plant the point of your pencil at this spot.
Stretch the string tight at a 90 degree angle from the layout edge.  Push the pin in when the string is tight.

Keeping the string tight, draw a half circle with the pencil.  Your drawn line will be 22" in diameter (11" radius).

Center your track over your drawn line.

This works.  I have actually built a model railroad with flex track, using this method to lay out curves.

Les

[mrmtox]

Maybe some high school geometry would help.  The circumference of a circle (the total distance around it) is equal to the value of Pi (3.14) multiplied by the diameter of the circle. The diameter is simply twice the radius.  Therefore the total circumference is Pi times twice the radius (2R). Sooo - an 11" radius curve generates a total circle of 69 inches of track that is 22" (twice the radius) wide. One-quarter of a curve = 17.3", one-half a circle = 34.5",  etc.  Pencil and string certainly works but if you're going to do a lot of curve layouts a couple of bucks invested in a simple set of dividers (available at most art supply stores) would sure make your life easier.

[NewConductor]

thanks all. so i did have the idea mostly right then. will use that string solution, seems like a pretty good way to do it.