BigRusty wrote: On my last layout, I pasted one of the easement templates available on poster board and then carefully cut out the edge with the track center line. I then used a a compass based on a retractible tape measure with a centering pin and a pencil at the outer end. I set the point for the radius center at 90 degrees from the tangent with a 1/2 inch offset and drew the curve. Then, I slide the template along the tangent until the curve of the easement intersects the curve. Draw the easement.Goes quickly.
On my last layout, I pasted one of the easement templates available on poster board and then carefully cut out the edge with the track center line.
I then used a a compass based on a retractible tape measure with a centering pin and a pencil at the outer end. I set the point for the radius center at 90 degrees from the tangent with a 1/2 inch offset and drew the curve.
Then, I slide the template along the tangent until the curve of the easement intersects the curve. Draw the easement.
Goes quickly.
I'm trying to get my head around this, so please bear with me.
I assume the template you mention is from the link I posted originally ?
When you say you cut out the edge with the track center line, is that the line marked "center line of track on spiral" on template C ?
If I understand correctly, you draw your tangent on the sub-roadbed and then the intended radius curve that will join the tangent plus 1/2" offset. e.g. with a 30" radius curve, the point for the curve is actually 30 1/2" from tangent track ?
Again, using template C as an example, you then line up the tangent line from the template with the tangent drawn on the sub-roadbed and slide the template until the "center line of track on spiral" curve on the template meets the 30" radius curve you have drawn on the sub-roadbed ? You then draw a curve from that point back to the tangent and you have your easment curve ??
Appreciate your patience in explaining how this works. I really would like to get a better understanding. I have the John Armstrong publication, but still can't quite grasp the concept.
Many thanks again
With all due respect to Linn Westcott, who was a true model railroading pioneer as well as a long-time employee of Kalpubco, unless you are laying out full-scale curves to be used by Acela, TGV or the Shinkansen the techniques and templates in that article are a gross overkill!
Simple, straightforward way to lay out easements (John Armstrong approved, have used it for decades and I know it works.)
1. Draw the centerline of your tangent (straight track) to a point at right angles to the center of the curve. This is the theoretical point of tangency.
2. Measure back the length of your longest car (in HO, an 89 foot humongubox is about 12.5" long.) You have just found the actual point of tangency.
3. Locate the center of the curve, at right angles to the tangent line, and measure radius plus approximately 1/24 the length found in 2 above (for this example, 1/2" is close enough.) The offset point should be marked and labeled theroretical point of curvature. Swing the centerline of the curve.
4. From the radius line found in 3, strike a chord the length found in 2. The point where that chord intersects the curve centerline is the theoretical point of curvature.
5. Find a point half way between the theoretical point of tangency (1 above) and the theoretical point of curvature (3 above.) That point, with the actual point of tangency (2 above) and the actual point of curvature (4 above) gives you the three points needed to establish the spiral easement. This can be drawn using a bent batten (John Armstrong's method of choice) or a limber piece of flex track (Atlas code 100 in HO works for me.)
If you are trying to spread track centerlines going into a multi-track curve, you can simply use a longer spiral easement into the inside track, more offset, and 24X offset for chord length and tangent setback. (Example - tangents 2" apart, curve radii 24" and 26.5". Outer curve as explained in 1 - 5 above. Inner curve offset 1", distance to APT and APC 24", or twice as long easement.)
Chuck (modeling Central Japan in September, 1964 - with spiral easements on all curves)
Hi there
I came across this article in MR http://trains.com/mrr/default.aspx?c=a&id=290 and am wondering if anyone would be able to find the time to answer some questions I have about laying out easement curves.
For example in Part B (d ) Points M and A directly in line with P. Where are points M and A located ?
I have some other questions but was hoping one of you who might be familiar with this article, or have a better understanding than I do, would be willing to assist.
Greatly appreciated
cheers