I am having some trouble understanding how to make easements. I’m planning the next stages of my layout expansion, and would like to include easements.
And it seems like it would be a pretty easy way to do easements : if I understood what he was talking about. Does anyone out there have drawings that could explain the before and after of what the auther means? For example, what the trackwork looks like w/o the easement and what it looks like with? That may help me understand… Or maybe someone can come up with a more step by step process that shows how to lay easements out?
Thanks in advance for your help!
Will be happy to clarify my question(s) if need be
Take a compass and draw a half circle. That is what an un-eased curve looks like. The problem, for a fast mainline, is that at each end of that curve will be a straight piece of track. If you are running tight radius curves, say 18", and put those on your main, the loco leaves the last straight piece of track, and accelerates nearly instantly sideways into an arc. That is not much dissimilar to being t-boned at an intersection. You are going straight, and wham, buddy’s car accelerates you really fast sideways, but you are also still moving forward, so in a tight curve. Now, that effect would be generated only by a train moving at over 120 scale mph entering an 18" radius curve, but the dramatic outcome would be nearly as bad…crash.
An eased curve looks sort of like a parabola. It starts off with very little curve, but the curve changes all the time, getting tighter, until, at the bottom of the parabola, it is in a tight curve that would have hurled the passengers sideways without it. An eased curve on a railroad is somewhat like that, but not nearly so flat and long on the ends of the curve.
Basically, an easement is a slow acceleration into a curve, or a change in direction. No easement, and the change of direction begins hard and can do damage; there is much greater force due to no real acceleration.
Thanks for that post. It helped quite a bit. Basically, it looks like you’re supposed to take a bit of the curve and straight out of the mix and blend the straight into the curve… I guess it’s a “slurve” or something.
One thing I’m unclear on, still. When you talk about the “offset”. If you have a 21" radius, and the offset is 3/8", assuming you’re making a full circle, would the straight sections of track on either side of the full circle (diameter) then be 42.75" apart from eachother? If that is the case, I could see where potentially this could be a space limiting problem for some, or at least maybe confusing when laying out track. I suppose you could gradually swing out your track 3/8" and then into the easement…
I suppose I should grab some track and practice this a bit
The centerlines of the straights would be 42.75" apart, so you are right on target. If space is tight, you would get better performance from eased 21" curves than uneased 22", or eased 20" than uneased 21".
The book “Track Planning for Realistic Operation” by John Armstrong, published by Kalmbach, has a good section on easements. That book is a “must have” for designing a layout. A lot of people find the “bent stick” method of laying out an easement the easiest and I’m surprised no one mentioned it so far. I’ll try to describe it. Here goes. Draw your two straight tracks at right angles to each other so that they form two sides of a square. Then draw the half-circle of your curve, but pull it back so that it is inside the square on both sides by the amount of the offset. That would be 3/8" for an 18" radius curve. Make marks on the straight track at the points directly opposite the centre of the curve. The easement is divided equally on both sides of these points. For an 18" radius, the easement should be 12", so the easement starts 6" before this point and ends 6" after it, at both ends of the curve. Now, take a thin flexible stick, and hold it in place with nails on both sides of it at both ends so it can slide, bend it around the curve. It should touch the straight track at the begining of the easements and touch the curve at the end of the easement and will follow the curve in the middle. In between those two points, the stick will take its own shape, and that will be the easement.
Looking over what I’ve written, it looks pretty confusing. Get the book. It’s got pictures. There was also an article in the “Back to Basics” column of MR about doing this, but I can’t remember which issue it was in.
If you connect a circular curve to a straight line, the place where they meet is the point of tangency or PT. The easiest way to do an easement is to just offset the PT by 1/2 in, so if the curve is 24" radius, then the straight part is 24 1/2" away from the center of the curve. Then start about 6-8 in on either side of the PT and bend a smooth curve in by eye.
While the resulting curve won’t comply with any engineering formula, it will look just as good and nobody will be able to tell the difference. If somebody whips out a ruler and starts measuring offsets, two or three good whacks with a baseball bat will discourage that.
Something you may find helpful after you practice making easements…I use 1/8" doorskins but masonite or illustration board would do., is make a pattern. I do it with a 6" tangent at one end of the easement, and 6" to 12" of desired radius at the other end. cut it just outside the line and finish it by sanding right to the line. Make one for each different radius you need. That way you can take it to any part of the layout and draw a centerline for your roadbed and track. To reverse the direction just flop it over.
Another point - if you can fit 22" radius uneased curves, you probably are FAR better off doing 21" radius with easements. Refer again to Track Planning for Realistic Operation (is there ANYTHING John Armstrong couldn’t figure out?) and see how the ‘lurch’ and coupler offset is LESS for a 18" radius curves with easements than it is for 22" radius curves without easements. Amazing! Also note the section of turnouts and substitution radius. In most cases, having a turnout lead into a curve automatically provides an easement effect as even a #4 turnout has a more than 18" substitution radius.
I was thinking about easements for my next layout and I thought I would bring this topic back to life instead of starting a new one for my question:
How much radius can safely be traded off for easements? In my current plan, I have stuck to a minimum 24" radius everywhere but have not used easements. I would like to operate 6 axle diesels and 50’ freight cars but no passenger cars (at the moment at least).
I did a little what-if study (I use 3rd Planit software so this quite easy) on one particular curve and found this. The original radius of the curve is 24" and it spans 100 degrees.
Using short easements, this changes as follows: the radius drops to 21.75" with easement lengths of about 5" on each side of the constant radius section.
Is this a fair trade off? I had to use really short easements to keep the radius even at this level. How much more radius could I trade off by using a longer easement?
There must be some kind of SEVERE hiccup in the 3rd Planit software, unless you have turnout points close to the point of tangency of the uneased 24" radius. For normal spiral easements, 1/2 inch offset, the curve diameter is only reduced by the offset - 24 inches becomes 23.5 inches.
Running short cars (longest is about 65 scale feet in US HO) I use a 10mm offset and extend the spiral 250mm in each direction from the theoretical point of tangency. Unless you are running Acela at prototype speed, 1/2" offset and 12.5 inches length in each direction should be sufficient for most US HO purposes.
Spiral easements also make it easy to widen track centers from tangent to concentric curves. Just make the outer spiral a “normal” spiral and make the inner spiral “longer” by making the offset ‘normal plus additional track center width.’ In both cases, the spiral is 50 times the length of the offset, half on either side of the theoretical point of tangency. The inner curve track peels off early.
Chuck (modeling Central Japan in September, 1964 - with spiral easements)
If you cannot find your handy/dandy 10-1969 Model Railroader — check out these three forum easement links and look for the words “bent stick” and MR’s Andy Sperando comments about how he uses the bent stick technique, and some other sage advice…
