Easements

[Anonymous]

Hey. I am trying to plan a HO scale layout. I am using a HO Scale Template made by CTT Inc. of Dallas, Texas. (the template is 1:12) The problem I am having is trying to make an easement. I have heard all sorts of things like tangents, and none of it makes sense to me with grade 8 math. I have heard about using flexible sticks and really long combinations of like a half inch of this radius ect. Thanks for your time, if it helps any the radius of my turns will be no less than 26" and no more than 32"
Thank you,
Morgan

[Anonymous]

Morgan,

The simplest way to do an easement is full size on you layout as you go. Draw you radius, then pick the point where the tangent track (straight) will depart the curve.Drawn your straight track from this point, but offset (to the outside of the curve) by 1/4 to 1/2 inch. Then pick two points - one down the stright track about 4 - 6 inches, and one on the curve about 4 - 6 inches in the other direction. Join these two points with your flexible stick to see your easement.

What you should end up with is the straight track transitioning through a slight "spiral curve" into the constant radius curve. Repeat for the other end of the curve!

Andrew

[Adelie]

Morgan, if you are trying to depict the easments on the plan I would not get too exact. Easy for me to say, I use CadRail which does depict them exactly, but for pencil and paper the important things to know are the offset between the curve and its adjoing straight section and the length of the easement between the two.

In the range of radii you are describing, you will wind up with an offset of about 1/2", and an easement length of about 18" total (9" on either side of the point where the curve and straight would join, known as the "point of tangency"). So, lay out your curves where you want them, join them with straight sections. Then draw a parallel straight 1/2" (to scale) outside of that. This will be the location of the actual adjoining straight section.

Once you do that, measure 9" either side of the point of tangency between the curve and the first straight line and carry it out to the offset straight line. If you then erase the first straight line and everything inside the two 9" measurements you just made, you will have the curve, the actual straight and the gap in between is the start and end point of the easement.

If all your curves are the same, you could make a template from that, but I'd be more likely to hand sketch in the joint between the two from there. I think it is easier to build them on a 1:1 scale than try to on a 1:12 scale.

[bogp40]

For a simple approach, use a pine spline (3/8x3/4). Pin it on the centerline of the staight and flex it to the desired radius. Works good enough as long as the pine selected if fairly clear/ straight grain. Not as exact as a cad program or drawn geometrically, but how exact do you need to be. Will set the easement automatically for any radius.
Bob K.

[Anonymous]

Thank you all. So I should be good then making my plan with no easments, it doesn't seem to me that they will be very big. Thank you all,
Morgan

[Sperandeo]

Hi Morgan,

I basically use the bent stick method of drawing easements that Bob Knapp described, except that I used that method to make illustration board templates for easements into my most common curve radii. You can see more detailed exp-lanations of the bent-stick method, including diagrams and dimensions, in the book "Track Planning for Realistic Operation," by John Armstrong (Kalmbach Books), and in the Novemeber 2001 "Model Railroader," pages 124-125.

As far as drawing easements on the track plan, I follow a recommendation from John Armstrong's book and simply offset the tangent (straight) track from the circular curve by the width of a pencil line. Since the actual offset on the layout is only 1/2" (or less, depending on your radius) for HO scale, that's sufficient to allow for the easement in planning. You do need to allow for the length of the easement to extend back into tthe tangent, as Mark explained. Basically, the tangent will be shortened by half the length of the easement, and you want to avoid locating any turnouts or crossings in that length unless you plan to build them by hand.

Good luck with your layout,

Andy

[Anonymous]

Here's an easier method for easements.

For the first 12" of your curve, use a curve that's TWICE the radius that you want for the main part of the curve. For instance, if you want a 22" curve, make the first 12" or so of it a 44" curve. Same thing as you go out of the curve.

The net result of this method is that you'll add approximately 1" to the effective radius of the curve.

The easement will smoothen out even more as you bend your flex track around the curve. You'll actually have troubles identifying exactly where the curve starts, which is what you're looking for.

Mark in Utah