track work

[Anonymous]

what do track layers mean by easements, as associated with turnouts ect.

[selector]

An eased curve is one where the curvature is not constant as soon as the curve is initiated. Instead, in order to spare sensitive cargo, like humans, on hi-speed turns, and to minimize damage or derailments, the track is eased into the curve by generating a spiral until the desired trajectory is met to get the curve to the next straight. Think of a curve that starts with a wide radius of 60", then shrinks to 40", and finally to the desired 30". A train entering the curve will hardly notice the accelerating laterally toward the outside of the curve as the loco follows the curve in the opposite direction. As the loco moves along the curve, the curve radius shortens, the curve tightens, and the loco begins to feel a bit more acceleration outward, as will its cargo. Eventually, at the apex, the acceleration stops because the rate of curvature is stable, and loco then progresses to an eased exit of that same curve...which would serve as a easement into the curve for a loco coming from the opposite direction.

[Anonymous]

Great explanation Selector!

The other issue with easements is executing them... There are many methods, ranging from eyeballing it to using advanced calculus.

I'm from the eyeball camp, myself. I typically start the curve about 1/8" for every 45 degrees of curve, further "out" than the exact radius would call for. That means you'll ease about 1/4" for a 90-degree curve and 1/2" for a 180-degree curve. You can make them bigger, but I didn't find it to be helpful or visually appealing. You can do less, but at that point you quickly start to defeat the purpose (IMHO).

Then I bend it evenly until the center of the track is exactly on the radius line to about 45 degrees of curve (or half the arc of the curve if less), continuing "on radius" from that point until it's time to start easing back "out" of the curve. Now, that means on a 90-degree curve or smaller, the whole thing is essentially 'eased' and that works just fine. On a 180 degree turn, you'll have about half your curve "easing" in-and-out (45 degrees on each end) and about half "on radius".

Of course, I use flextrack and a large compass to draw out my radius lines, which is a large help toward this end...

[tomikawaTT]

Another, as yet unmentioned, reason for using a spiral easement is to minimize the side thrust of body-mounted couplers. Long cars that would be pushed sideways off the rails at the start of an un-eased 30" curve can be babied into taking 24" by a long, gentle easement. This also keeps the diaphragms on passenger cars lined up.

[Anonymous]

THANK YOU FOR THE REPLIES IT NOW CLEAR TO ME WHAT REQUIRED TO CURVE THE TRACK.
REGARDS
PATRICK O'NEILL

[Don Z]

Okay....I guess I'm having a dense day or something, because I just don't get it! I've read and re-read the responses, and it doesn't make any sense....let's just say that I wasn't in school the day the math teacher talked about tangents and all that.

Can somone explain it in simpler terms so I can have a 'light bulb moment'? Am I supposed to start my curve outward before it starts turning in to round the bend? If so, how does turning the opposite direction help the train get around the curve?

Confusedly yours,

Don Z.

[tomikawaTT]

Don,

To create a spiral easement:
1. Lay down the centerline for your curve.
2. Lay down the centerline of your straight track so that it misses the closest point of the curve centerline by 1/2 inch.
3. Find that closest point. It will be where the curve diameter is at a 90 degree angle to the straight track.
4. Measure from that point 25 times the offset distance along the straight track line.
5. Fasten something that will spring uniformly along your straight track line, starting at the last mark you made. Anchor at least 6 inches of it (working away from your curve.)
6. Working from the opposite end, pu***hat flexible item until it can be matched up to the curve you want. The total length of the outward spiral should be about 50 times the offset you found in step 3. It should cross the point of tangency (that's where you measured the offset) halfway between the curve centerline and the straight track (AKA tangent) centerline.

A 36 inch length of flex track with a free-sliding rail (Atlas, in my case) will form its own spiral if laid as described above. Also, if you are going to superelevate your curves, the outer rail begins to rise at that point 25 times the offset from the point of tangency, reaches 1/2 superelevation at the point of tangency and full superelevation at the point where the true curve begins.

Try this with a length of Atlas flex on a piece of plywood. It's easier to do than to explain.

[Don Z]

QUOTE: Originally posted by tomikawaTT

Don,

To create a spiral easement:
1. Lay down the centerline for your curve.
2. Lay down the centerline of your straight track so that it misses the closest point of the curve centerline by 1/2 inch.
3. Find that closest point. It will be where the curve diameter is at a 90 degree angle to the straight track.

Okay, here's where I get confused...if I have a straight track leading into a 30" radius 90 degree curve, why would the centerlines of the straight track and the curve NOT be in line with each other? In step 2, is the straight track supposed to miss the centerline of the curve to the outside of the curve? I'm sorry I'm not getting it at all.....

I appreciate the explanation, but maybe it's going to take someone showing me before I understand it. I did my track design with XTrkCad, and had the easement button set to broad. Does the program automatically adjust my curves so if I trace the full size printout, my easement worries are in my imagination?

Anybody need benchwork built in trade??? [:D]

Don Z.

[selector]

To see an eased curve, place a thin slat of cedar or some flexible wood in a vice so that about 1/6th of it is anchored by the jaws. Then placing a finger against the free end, deflect that end sideways along one of the flat sides of the slat. If you can, bend it about 6" sideways. Look at the curve from the jaws to the tip. See how the curve begins at a shallow angle, and then gets much sharper toward your finger? That curve is eased.

[CascadeBob]

The explanation of how to do a curve easement that I've found most useful can be found in "Track Planning for Realistic Operation", Third Edition by John Armstrong. This is a Model Railroader book. The descriptions can be found on pages 75 and 78. And a description of how to layout an easement can be found on page 116. I think you'll find the layout procedure on page 116 to be very clear. I've used this method in the past on my own layout and it works well. I've used a section of flex track to create the easement section from the straight track to the circular curve.
Hope this helps.
Bob

[Don Z]

Thanks to all who have tried to help me understand the easement. I looked through my collection of books last night, thinking I owned the John Armstrong book Bob mentioned. SInce I couldn't find the book, it's on order from Amazon.

I did find a drawing of an easement curve on trackplanning.com's website, so at least I know what the curve should look like now.

Thanks again!

Don Z.