I like the "bent stick" thing, and if the layout builder is anal about a specific radius, then a little bit can be added to the benchwork, to accomodate the "bent stick" easement, with out any problems.
If that creates problems with the isle way dimensions, than a compromise is going to have to be made.
It seems like this easement thing, which is so easy, can get too technical in it's explaination.
Bent stick it is, which is what I did, without knowing it was called the bent stick, I just wanted to work as easy as I could into the 24"r. on each end of my layout.
Mike.
My You Tube
If you look at the lobe in the upper middle of the track plan, the centerline on each side swings back down and toward the interior. In that case the maximum radius can be used and the easement moved down where it can be placed past the maximum width of the benchwork, lower down.
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As I think Jim mentioned, When the benchwork depth is fixed but length is available, a slightly larger-radius end curve of more than 180° can be used if the track is brought back in narrower after the curve for the desired clearance.
I used the original poster's 57-scale-foot figure to come up with an easement (and tangent) length of 12½" for 1½ car lengths in HO. When curves are very short, as these are in bringing the track back to parallel, a broader radius is much more space-efficient than trying to fit in easements.
Edit: Oops, I goofed. There's no need for 1½ car lengths on the tangent. 1 car length should be fine. But I won't take the time to rework the diagram.
Byron
Layout Design GalleryLayout Design Special Interest Group
A picture is worth a 1000 words.
It takes a 1.5 increase in width from the normal width 29 x 2 = 58 inches to accomodate the 18 inch long easement (1 to 1.5 car lengths, 2?). A 30 inch minimum would require a diameter of about 61.5 inches. Not that OP was concerned about a 30 inch diameter curve.
If I work backwards, with 60 inch diameter benchwork and leaving 1.5 inches from the edge on each side (skimpy, IMO), that leaves 57 inches for the diameter of the total curve, or bout 55.5 inches using the radius at the apex. OP should plan for a 27.75 inch radius using a standard 1 to 1.5 car length, maybe 2 car length, easement.
3 inch buffer on each side would reduce the minimum radius to 26.25.
- Douglas
ROBERT PETRICK cuyama Doughless The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space. That's not a spiral easement. I’ve observed a significant difference when a real easement is used. A "bent-stick" easement of 1-to-1½ car length seems to help a lot and doesn't take up much room*. This approximates a true mathematical spiral easement, the complexity of which doesn't seem to add much benefit in the model. * But there's no free lunch, there is some tangent (straight) track lost to the easements. The trade-off is often worth it. Byron I agree. No free lunch, you gotta pay the piper. Consider a full 180-degree horse shoe curve, with an easement into the curve and an easement out of the curve at the far end. And remember our 60-inch width constraint. Whether you use the fake pseudo easement mentioned above (a short 30-inch radius piece followed by the main prevailing 29-inch radius piece) or an official spiral transition (derived using complex mathematics), the point of curvature will slide along the tangent, making the whole curve longer than you think. But more importantly, the radius of the middle piece of the curve will become less than 29 inches, and depending on how long the transition easements are, it could become considerably less than 29 inches. Math is hard. Robert
cuyama Doughless The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space. That's not a spiral easement. I’ve observed a significant difference when a real easement is used. A "bent-stick" easement of 1-to-1½ car length seems to help a lot and doesn't take up much room*. This approximates a true mathematical spiral easement, the complexity of which doesn't seem to add much benefit in the model. * But there's no free lunch, there is some tangent (straight) track lost to the easements. The trade-off is often worth it. Byron
Doughless The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space.
That's not a spiral easement. I’ve observed a significant difference when a real easement is used.
A "bent-stick" easement of 1-to-1½ car length seems to help a lot and doesn't take up much room*. This approximates a true mathematical spiral easement, the complexity of which doesn't seem to add much benefit in the model.
* But there's no free lunch, there is some tangent (straight) track lost to the easements. The trade-off is often worth it.
I agree. No free lunch, you gotta pay the piper.
Consider a full 180-degree horse shoe curve, with an easement into the curve and an easement out of the curve at the far end. And remember our 60-inch width constraint.
Whether you use the fake pseudo easement mentioned above (a short 30-inch radius piece followed by the main prevailing 29-inch radius piece) or an official spiral transition (derived using complex mathematics), the point of curvature will slide along the tangent, making the whole curve longer than you think. But more importantly, the radius of the middle piece of the curve will become less than 29 inches, and depending on how long the transition easements are, it could become considerably less than 29 inches.
Math is hard.
Robert
I agree, but I think you are describing a situation where you want to keep the entire curve within the confines of the current benchwork plan. The gentler and more you lengthen the spiral easement, the more the radius at the top of the egg has to get narrower, so to speak.
I think the question is, in order to keep the radius at a minimum 30 degrees, how much more benchwork will you need to have "proper" spiral easements. (the term "proper" being a variable of course). IMO, its going to take more than 1/2 inches of benchwork, which I think was the suggestion. Quite a bit more than 1/2 inch by simple intuition, not actual math however.
You can have a 60" constraint and still have easement. How? You make the curves more than 180 degrees so they bend inward. The easement can be there.
ROBERT PETRICKBut more importantly, the radius of the middle piece of the curve will become less than 29 inches, and depending on how long the transition easements are, it could become considerably less than 29 inches.
I don't think so. It's the offset that determines the width of the overall turnback curve (and thus, in this hypothetical, the radius of the curve), not the length of the easement.
Math may be hard, but bent sticks are easy-peasy.
LINK to SNSR Blog
DoughlessDescribing it as a spiral easement of 1 to 1-1/2 CAR LENGTHs makes more sense to me. The longer the cars you plan to run lengthens easement generally needed.
And longer is better, if one can spare the room. But often, my clients' desires to get the absolute most out of a given space mean we go for the shortest easements that still help.
cuyama Doughless The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space. That's not a spiral easement. I’ve observed a significant difference when a real easement is used. A "bent-stick" easement of 1-to-1½ car length seems to help a lot and doesn't take up much room*. This approximates a true mathematical spiral easement, the complexity of which doesn't seem to add much benefit in the model. Prototype easements are often used to transition to-and-from super-elevation, so they need to be longer. * But there's no free lunch, there is some tangent (straight) track lost to the easements. The trade-off is often worth it. Byron
Prototype easements are often used to transition to-and-from super-elevation, so they need to be longer.
Thanks Byron. I think the real reason we want the kind of easements we build in modeling is to help equipment operate better, as to not lurch directly into a curve. That was probably more of a problem in Armstrong's day when curves were tighter, but it could still be a problem today with longer cars.
Describing it as a spiral easement of 1 to 1-1/2 CAR LENGTHs makes more sense to me. The longer the cars you plan to run lengthens easement generally needed.
OnewolfThat's exactly what a (spiral) easement is?
Not exactly. A true spiral easement (or the "bent stick" approximation) goes from tangent (straight) to the desired radius.
OnewolfThe objective is no 'lurching'.
Agree. It also helps longer equipment negotiate tighter curves.
Doughless But for modeling the prototype, I really don't see the point of avoiding lurching into a 29 inch radius curve from tangent by first lurching into a one inch long 30 inch radius curve from tangent. I'd think you'd want to start off with something like an 84 inch radius and then spiral down from there over the course of a few feet.
But for modeling the prototype, I really don't see the point of avoiding lurching into a 29 inch radius curve from tangent by first lurching into a one inch long 30 inch radius curve from tangent. I'd think you'd want to start off with something like an 84 inch radius and then spiral down from there over the course of a few feet.
That's exactly what a (spiral) easement is? And that's how I have (tried) to lay my track. The objective is no 'lurching'.
Modeling an HO gauge freelance version of the Union Pacific Oregon Short Line and the Utah Railway around 1957 in a world where Pirates from the Great Salt Lake founded Ogden, UT.
- Photo album of layout construction -
DoughlessThe example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space.
riogrande5761 Onewolf Doughless I don't understand the need for easements either, depending on the radius. Of course I run all of my trains at 25 mph or less. But our layouts all have terribly sharp curves compared to the prototype, so I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius. Speed exacerbates the sway, not the nominal difference in radius. JMO. Seems to me to really gain the visual effect, easements are going to have to be pretty long and space consuming. I think having easements makes a huge improvement in the visual effect of running model trains specifically because the curve radius is so much smaller than the 'real' world. I don't see any downside to using easements other than the slightly more space required. Me neither. After I had devoured my copy of John Armstrongs book in the mid to late 1980's, it was a no-brainer to include easement in my first 16x19 layout and I've been doing it every since. The slightly more space of about a half inch isn't so space consuming as some suggest.
Onewolf Doughless I don't understand the need for easements either, depending on the radius. Of course I run all of my trains at 25 mph or less. But our layouts all have terribly sharp curves compared to the prototype, so I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius. Speed exacerbates the sway, not the nominal difference in radius. JMO. Seems to me to really gain the visual effect, easements are going to have to be pretty long and space consuming. I think having easements makes a huge improvement in the visual effect of running model trains specifically because the curve radius is so much smaller than the 'real' world. I don't see any downside to using easements other than the slightly more space required.
Doughless I don't understand the need for easements either, depending on the radius. Of course I run all of my trains at 25 mph or less. But our layouts all have terribly sharp curves compared to the prototype, so I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius. Speed exacerbates the sway, not the nominal difference in radius. JMO. Seems to me to really gain the visual effect, easements are going to have to be pretty long and space consuming.
I don't understand the need for easements either, depending on the radius. Of course I run all of my trains at 25 mph or less. But our layouts all have terribly sharp curves compared to the prototype, so I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius. Speed exacerbates the sway, not the nominal difference in radius. JMO.
Seems to me to really gain the visual effect, easements are going to have to be pretty long and space consuming.
I think having easements makes a huge improvement in the visual effect of running model trains specifically because the curve radius is so much smaller than the 'real' world.
I don't see any downside to using easements other than the slightly more space required.
Me neither. After I had devoured my copy of John Armstrongs book in the mid to late 1980's, it was a no-brainer to include easement in my first 16x19 layout and I've been doing it every since. The slightly more space of about a half inch isn't so space consuming as some suggest.
Well, its still a brainer for me. I guess its a matter of what the book was calling an easement and what Armstrong was looking to solve. I doubt if he was talking about a prototype easement scaled down to its modeled length. I think Armstrong is talking about avoiding violent lurch to help model trains or toy trains (back in the day) operate at high speeds. Which might be the goal for many.
riogrande5761allow for that half inch when designing the sub-roadbed and draw in the centerlines.
My point was that since you had to plan the centerline before laying the track, the natural tendency of Atlas flex to create an easement provided no value.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
carl425 Onewolf One of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to Yeah but... I lay my track on homasote or cork roadbed, which is laid on plywood cookies. By the time the track goes down, I've already committed to the center line.
Onewolf One of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to
Yeah but... I lay my track on homasote or cork roadbed, which is laid on plywood cookies. By the time the track goes down, I've already committed to the center line.
Here is the thing. All you have to do is allow for that half inch when designing the sub-roadbed and draw in the centerlines. Cork is laid similar to the flex track, you lay the halves on the centerline and they also do a "bent stick" easement through the offset and to the offset tangent cetnerline. Here you can see the centerline on the subroadbed
Since the cork is laid on the centerline which has easements factored in as the above diagram shows, the flex track on top will have easements too.
cuyama Doughless I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius Because of what John Armstrong colorfully called "the coefficient of lurch" in Track Planning for Realistic Operation, the straight-to-curve transition is often the critical point for performance and reliability of specific railcars or coupled combinations. (Which is intuitive.) In my experience, an adequate easement may allow a piece of equipment to negotiate a tighter radius than an un-eased curve. For track plans where a couple of inches of reduced radius makes a difference whether a turnback curve will fit in the room or not, it matters a lot. (And these situations are common.) Testing has been started to measure the actual benefit of a “bent stick” spiral easement in terms of radius. Quick rough tests suggest that it might be the equivalent of a couple of inches of radius for some classes of HO curves. But more work is to be done to characterize the benefit conclusively. Byron
Doughless I'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius
Because of what John Armstrong colorfully called "the coefficient of lurch" in Track Planning for Realistic Operation, the straight-to-curve transition is often the critical point for performance and reliability of specific railcars or coupled combinations. (Which is intuitive.)
In my experience, an adequate easement may allow a piece of equipment to negotiate a tighter radius than an un-eased curve. For track plans where a couple of inches of reduced radius makes a difference whether a turnback curve will fit in the room or not, it matters a lot. (And these situations are common.)
Testing has been started to measure the actual benefit of a “bent stick” spiral easement in terms of radius. Quick rough tests suggest that it might be the equivalent of a couple of inches of radius for some classes of HO curves. But more work is to be done to characterize the benefit conclusively.
Oops, I meant entering a curve with a 1 inch LARGER radius than the prevailing radius.
I understand the principal conceptually. But how much space does it take to do easements properly? There is always a lurch with our tight radius (compared to prototype) layouts, unless we take gobs of space to go from tangent to the prevailing radius. The example given was starting off with an easement of about 30 inches to a prevailing radius of 29 inches to take up the same amount of space. I didn't see much difference, or much of an easement, in that situation. And that application seems to be most likely in our layouts.
I can see where going from tangent to 72 inch radius, to 60, to 50, to 40, to finally 30 eases equipment into the curve, but that takes up at least a foot of linear space on either end of the curve if not more. There is no doubt that "proper" easements take up a lot of space.
Thanks guys, you're always very helpful! :) I will be running a switching layout at slow speeds with 4 axle diesels and longest car is 57 ft (scale equivalent). Time period is the early 90's. I am using atlas flex track so will be putting in the easements.
DoughlessI'm not sure of what real gain there is entering a curve with a 1 inch smaller radius than the prevaling radius
OnewolfOne of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to
In TPFRO, Armstrong explains that an eased curve of a tighter radius performs better that an un-eased curve of a larger radius. So... if you need to reduce your radius by 1/2" to fit in easements, it's worth it.
I think about driving a car down the road at 50 MPH and going into a turn. Unless you're a F1 driver, as you slowly turn the wheel to start the turn you have created an easement which greatly smooths out the transition of the curve. However if you immediately turn the steering wheel from 12 o'clock to 9 o'clock (which is what a train does when entering a curve with no easement) everyone leans and slides to the right.
PRR8259 In the model world it is perfectly acceptable to layout easements by eye. I personally used sectional track on my layout. Using one piece of the next larger radius at each end of a curve gives nearly the same performance, in the model world, as if one actually followed the (simplified) easement geometry in the layout design books, or else "curved by eye" the transition. Personally, if I had a 30" radius curve, I am not sure that I would bother trying to do an easement, because at that radius, unless running high speed passenger equipment, there isn't much of a "sway" affect as what happens in real life when there isn't an easement. I used Kato 26.375" (converted U.S.) radius, with 28.75" radius sections at each end of a curve on my mainline, to provide the "easement effect". Later when I enlarged some curves to 30" or 32" radius I didn't worry about easements or rather just curved them by eye. The long 89' or 92' freight cars do just fine for me...I do recommend laying one out and then, if possible, testing the equipment to see how it looks, before finally gluing or nailing the trackwork down in place. John
In the model world it is perfectly acceptable to layout easements by eye. I personally used sectional track on my layout. Using one piece of the next larger radius at each end of a curve gives nearly the same performance, in the model world, as if one actually followed the (simplified) easement geometry in the layout design books, or else "curved by eye" the transition. Personally, if I had a 30" radius curve, I am not sure that I would bother trying to do an easement, because at that radius, unless running high speed passenger equipment, there isn't much of a "sway" affect as what happens in real life when there isn't an easement. I used Kato 26.375" (converted U.S.) radius, with 28.75" radius sections at each end of a curve on my mainline, to provide the "easement effect".
Later when I enlarged some curves to 30" or 32" radius I didn't worry about easements or rather just curved them by eye. The long 89' or 92' freight cars do just fine for me...I do recommend laying one out and then, if possible, testing the equipment to see how it looks, before finally gluing or nailing the trackwork down in place.
John
gregc IDRick The appropriate easement is 1/2 inch per side. Does this mean the net radium of the half circle is now reduced to 29"? no. the curve widens to 30.5", becoming an ellipse.
IDRick The appropriate easement is 1/2 inch per side. Does this mean the net radium of the half circle is now reduced to 29"?
no. the curve widens to 30.5", becoming an ellipse.
Echo's approx what I posted ealier.
The diagram is basically what John Armstrongs books illustrated; a must read IMO.
Onewolf One of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to as opposed to the much stiffer ME track which must be meticulously bent to form easements.
One of the great things about Atlas flex track is that it naturally forms beautiful easements if you allow it to as opposed to the much stiffer ME track which must be meticulously bent to form easements.
Yet for some reason there are those who prefer the stiff "flex" track. As you noted Doug, Atlas forms it's own easements nicely.
IDRickThe appropriate easement is 1/2 inch per side. Does this mean the net radium of the half circle is now reduced to 29"?
greg - Philadelphia & Reading / Reading
Hi IDRick,
IDRickDoes this mean the net radium of the half circle is now reduced to 29"?
You are correct. What you have to decide is whether or not an easement will make any difference to the appearance of your trains as they go through the curve. IMHO, the difference is related to the speed at which your trains go through the curve. If you are running slowly then the lack of an easement won't be as obvious, but if you are running at higher speeds then the scene will look better with the easement. Your trains won't be suddenly 'launched' into the curve like an O scale toy train on tight radii.
The difference will be subtle, but I much prefer the easement option.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
IDRickadd a half circle of track (30-inch radius). The appropriate easement is 1/2 inch per side. Does this mean the net radium of the half circle is now reduced to 29"?
The radius would be 29 1/2 inch since each 1/2 inch is out of the 30 on its side.
Alternatively you could add it to the outside and your over all width for a half circle would be 61 inches - 30 1/2 inch per side.
Or you could split it so that you reduce your radius to 29 3/4 and widen your half circle by 1/4 inch on each side for a half circle width of 60 1/2 inches.
Paul