for starters use the length of your longest car.  For a simple layout with flextrack, move the center point of the track in the curve away from the center of the curve (center of the circle containing the curve)

This will make the radius of the mid-point smaller but give you a nice and simple easement.

Here's a picture which reduced a 24 inch radius to about 21,5 inches (at the middle) but made a smoother curve.

Great ... what is the offset you used? Like, 1.5" for example? And how did you determine the offset?

In my case, I use masonite spline roadbed and it gives natural easements - so no worries there.

Try this pdf on the Model Railroader site.. it has a nice explanation of easements and using the bent stick method as part of the article about reliable passenger operation:

www.trains.com/mrr/objects/pdf/september_web_reference.pdf

I had decent luck using 1/4" offset in N in the past. You could use 1/8" just fine. My current layout used 11" curves and I let the CAD program draw them in so I am not sure what the offset would be. It has been recommended that you use a car length or more (1.5x being ideal from my reading, not my experience..), about 4"-6" depending on the era. This means half of that comes from the tangent leading to the curve, the other half from the curve itself.

Any easement, even if it is not of ideal length, is better then no easement..

If you can't get that pdf, then try searching google for "bent stick method easement".

Chris

The offset is abut one inch - determined by trial and error mostly - moved it out and tried some cars over the track.The ties in the picture are those of the original 24 inch radius with no easement.  When I found out it did not run well I moved the rails and respiked - not a scenic location so I did  not need all the ties - just added enough to hold the rails..

Art

In N scale, I've had good results with 6" (80 scale feet) length easements up to around 13" radius. That's with about a 1/8" offset. I've mostly let the flex track form the easement, so it's not a perfect spiral easement -- more like John Armstrong's "bent stick" approach.

For more recent eras with a lot of longer rolling stock, you might want to go longer, or if you are depicting a wide open main line out in the country, longer easements will look a little more realistic (if you have the space). Mine are mostly for reliable performance, especially when shoving cars.

In tighter industrial and yard areas, the extra length of the easemented curves begins to come into play in limiting what you can do in a given space, so I tend to go for the shortest easements that do the job.

Submitted by Cuyama on Thu, 10/22/2009 - 16:18.

the extra length of the easemented curves begins to come into play in limiting what you can do in a given space

Just to emphasize this great point Byron mentions here.. when I first started drawing out plans using easements it was a bit of a shock how much length they took up, even in N scale. It doesn't impact the width of a turnback very much (that is, the effective radius) but the length of the turn.

Not sure I am making sense..

What was happening was between two curved segments I had less tangent ("straight track") with which I could work in sidings and what-not. If you think of a 3x6 with a curve at both ends, say 12" R.. you would expect that with 1" of space between the track and the edge of the layout it would take 13"x2 or 26" of your your 72". However, a 6" easement would add 3" to each end taken out of the tangent making it closer to 32". If you have multiple curves in a given area it adds up to even more, each curve taking its little 6" bite of easement track.. I was finding the the cumulative effect of these was really impacting what I could do.

I bring this up because as a beginner (and now as a slightly more experienced beginner..) this was something I did not account for in my sketches and it resulted in a lot of "things not fitting". Just food for thought.

Chris

Back in the 80s there was an article in MiBa which presentet a formula for computing the offset.

it goes like this: f=L² / 24R 

L= the length of the easement

R= Radius of the curve

f=the offsett of the tangent

I have used this one for a  long time, and also use it these days when I need to compute my easement accurately in the CAD program 3rdPlanIt.

You could download the free demoversion of 3rdPlanIt, draw the curves you like with easement and print them out in 1:1.

Like Joe, I have some spline roadbed where it will owrk (open areas) but for towns on plywood I prefer the flexible yard stick. It has never done me wrong. the trick is getting the wife to draw the line when you hold it in place. Thats the problem with only two hands you need a third to hold the pencil.

Another tool is a thin piece of masonite say 6'-8' long.

I'll try with 6" x 1/4" easements - when i get home, that is.... i'll just build a 'test' curve, and experiment with different radii and easements to find out which will allow me to run incident free :)

Martin

Sorry Guys,

     I'm still confused, Is there a web page that could possibly show in two different colors the before and after?

in the same radius, an overlay, so to speak? The description here measures, or only shows the radi is larger in the center of the radi. What happens at the start of the curve? I thought that is where you have to make the changes. I'm modeling in "O" scale two rail and it is very important for me to get it right the first time. Currently I am working with 40.5 inch track. Should I change to flex trax?

     Avis