Yeah, its a dumb question. Everyone else knows what it is. Except…me. I feel like it is one of those things that is often discussed in the hobby but goes with the general assumption that everyone knows what it is. The reason I’m asking is I see that it is supposed to visually improve something about trains and curves, and I am all about that. So…what is it and why is it used?
An Internet search for “model railroad easement” will yield lots of results, many of them useful. Here’s one from our hosts:
http://mrr.trains.com/how-to/track-planning-operation/2017/05/easy-easements-for-model-train-track
The horizontal easement is basically a spiral curve transitioning from straight track to the desired curve radius. Easy with flextrack or handlaid. Longer easements work best, but even a short one helps. I try for a length at least equal to the length of the longest car or locomotive – more if there’s room.
Edit: One also needs vertical easements when changing grade. The steeper the grade and the longer the cars, the longer the vertical easement.
An easement is a gradual adjustment vertically or horizontally to change depth, height, grade, or radius to a smoother transition.
Think of it like this,… If only the roller coaster was just a little bit more of a smoother ride. You probably wouldn’t want to go on it anymore, but trains love this.
Imagine 2 pieces of sectional track, one straight, one an 18" radius curve.
There is an abrupt change, there is no easement.
Now imagine you have a wooden yardstick. Instead of a normal yardstick, this one is only 1/3 the usual width, so it bends without snapping.
Bend it into a curve. It is a different shape than the curved sectional track. At first the diameter isn’t as much. It increases to match the desired radius. You don’t see the lurch as your train hits the curve.
John Armstrong explains it here:
You know what I never understood is easements are only considered in curves or radius. Easements should also be considered in grade adjustments. Adjusting from Flat (level) to the start of a hill. There is an easement in the beginning of a grade as well.
Vertical easements are considered by thoughtful designers – but ignored in many (most) published speculative plans.
Forgot I had made this graphic
My bad, I only think in one plane at a time. Given what I read in an unrelated thread, I have to take responsibility for this omission being the beginning of the end of the hobby. [:D]
That’s true. But it’s not just the visual part. Your trains will run better, too.
Here’s one reason: Grab yourself a couple of 89’ trailer flats, either really or just in your head (really is better). Now, wander over to some trackage where some straight track meets a (non-eased) curve. Put the two cars on the track, one on the straight section, one next to it, on the curve.
You will see some pretty impressive off-setting of the couplers. This ain’t just visual. And it ain’t just the couplers. It affects the whole car as it goes from the straight to the curve, compared to its neighbor.
What an easement does is change from straight to full-curve gently. And, in doing that, it lessens the amount of offset of the car ends and the couplers.
A longer easement is always better than a short one. My buddies all like a 12" one, because that’s the length of a passenger car. Or a trailer flat.
On my trackage, I stretched that out to 18", because it was easy to do, under the circumstances. It looks great. And it works great. Zero derailments.
Ed
Those green things are vertical curves, not easements. Ideally, the beginning and end of each vertical curve will have an easement. Note my useage of the words “beginning” and “end”. Yup, an easement at each end of those three green curves is appropriate.
Is
Are real easements necessary here? Probably not, if the curves themselves are gentle enough.
Ed
Ed, it is both. It is surely a vertical curve, but it also qualifies as an easement. It serves as an easement into and out of a constant grade (there is no lurch we need to worry about). We are concerned only with the secure grips of the couplers and the lower lips of the pilots on the locomotives. Well, I guess the trip pins as well.
It’s a vertical easement that keeps things from being suspended (spinning drivers), separated (couplers) or grounded (trip pins or low pilot leading edges).
Tom,
I see how you can say that putting those curves in so that there isn’t a “corner” could be an easement. 'Cause it certainly eases things compared to having an angle.
But it’s not the kind of easement we’re talking about. THAT kind of easement has a gradually decreasing radius of curvature. Which is not noted in the example. As far as I can see, it’s a simple curve of a single radius.
I certainly agree that having the curve at all is a HUGE improvement. And I again assert that a true easement is likely unnecessary.
Ed
Think of it this way if you’re going to go to a steep 4 degree grade from level. You would start from a zero degree grade to a 1 degree grade to a 2 degree grade to a 3 degree grade to your 4 degree grade all gradual.
If you go from a tangent into a radius the same thing applies. Instead of jumping right away into a 24 radius curve. Start with a 30 adjust to a 28 go to a 26 to get to your 24 radius curve.
Gradual gradual gradual[;)]
The term “vertical easement” is used fairly widely in the hobby for spiral curves leading into and out of grades.
Edit: I think I drew them as spiral curves with a CAD program. It would be pretty hard to bend that plywood into a true circular curve in any case – ½" or thicker plywood forms its own (near) spiral curve when bent (if properly supported).
Technically, those green things are called vertical curves, and they are parabolas, not spirals. They form smooth transitions to and from the forward and rear tangents. Calculations are based on the specified (or desired) length of curve and the algebraic difference between the grades of the tangents and a special constant called the k value.
Robert
If you say so, I’m certainly not a mechanical engineer (nor do I play one on TV). In actual practice, bending thick plywood roadbed (just like bending a stick for a horizontal easement) forms a reasonable approximation of a spiral curve – and most importantly, it works great. Folks have been calling it a vertical easement for a long time in the hobby.
Edit: I think that the most important thing is that these vertical transitions (by whatever name) are necessary for smooth operation, even more so with steeper grades and/or longer cars. The majority of published speculative track plans don’t include them, which effectively makes the grades shorter and steeper (sometimes comically so) than claimed.
Now that the replies have made the answer to the question crystal clear [(-D], I am reminded of the Supreme Court considering the issue of pornography. As one judge remarked, “I can’t define it, but I know it when I see it.”.
I am in the middle of building a new layout, and my desired minimum radius on curves is 32". I have a number of Ribbonrail track alignment gauges with a 32" radius that I fit into the sections of flextrack that make up the curve. What I have noticed is that the beginning and end of these curved sections are actually broader than the 32" radius in the middle of the curve.
So, in my observation, the broader radius at the beginning and end of the curve “eases” the locomotive and trailing cars into the 32" radius in the middle of the curve instead of doing it abruptly. That said, I still can’t define an easement.
Rich
as a corollary to this discuss of vertical easements, if you are using the WS incline system, is the vertical easement built into the system?
Oct. 1969 MR has an article about easements and includes fold-out templates.