The WWSL
Polson Canyon is a prototype scene of the right of way along the St Paul River. See Polson Canyon xxx.
Project Process
Polson Canyon is a series of cosmetic reverse curves. There will be 23 elements in its construction:
Pic
- easement - simple curve - easement - Bridge N4 (tangent)
- easement - simple curve - easement - North tangent -
- easement - simple curve x2 - easement - Bridge N3 (tangent)
- easement - simple curve - easement - Rock wall (tangent)
- easement - simple curve - easement - Bridge N2 (tangent)
- easement - simple curve x2 - Tunnel 1 (the left half of a turnback curve)
1. Pre-Installation Process - Track Preparation. See 4.2.3 Straight Track for the standard track preparation process.
Rail end checks. No changes or additions.Tie spacing. I do not change tie spacing on curves. There is no significant visual difference between WWSL Standard 1 and Standard 2 on curved track.
Track cleaning. No change or additions.Individual spare ties. No change or additions.
2. Installation Process
Easement. The easement on the cosmetic Reverse Curve is a 5 inch 28 inch radius between the tangent (straight) track and the 26 inch curveSuper-elevation. On the WWSL there is no requirement for super-elevation on these curves.Join Track Sections. There are several changes or additions when laying out curve track. Getting a smoothly flowing connection between tangent (straight) track and the curved track is difficult. The outward pressure of the rail at the joint often creates a kink.To minimize this difficulty I measure the curve circumference and, at the workbench, I take the required lengths of flex track, insert the rail joiners and solder each section together (without a gap) forming a single long, straight section. This is the only instance where I recommend soldering rail joiners. Be sure that its the best soldering job - blobs will interfere with the inward moving through the tie platesI place the moveable rail on the inside of the curve.I used Ribbon Rail curve templates to form the desired radius. If the curve is a compound curve, the appropriate Ribbon Rail curve radius template is added to the curved flextrack section. I then take this piece to the layout to install on the curve. I do an initial fit to see what works and doesn't work. This usually involves shifting the full curve template outward to meet the point of tangentcy.Glue Down. I layout the curve using the foam board curved track template instead of a straight edge. The curved template is fastened by a screw into the subroadbed. (another reason why I don't use a center line for roadbed layout lines).Tie Gaps. Fill those gaps at the rail joiner with the replacement ties.Rail Gaps. There are NO rail gaps in the simple or compound curve. The rail gaps are located on the straight sections several inches on either side of the curve.
Construction
Construction of the Polson Canyon Reverse Curve beginss at both ends and finishes in the middle along the roack wall
Laying out a cosmetic curve
Join Track Sections. There are several changes or additions when laying out the reverse curve track. Getting a smoothly flowing
connection between tangent (straight) track and the curved track is difficult. The outward
pressure of the rail at the joint often creates a kink.
I install the turnout per 4.2.5 Turnouts. I place the moveable rail on the outside of the divergent turnout track.
the traditional reversed curve
An example:
Two alternatives to model
1. simple curve has three elements: simple curve - tangent - simple curve
2. compound curve has seven elements: (easement - simple curve - easement - tangent - easement - simple curve - easement
Modeling Information
The use of tangent track between the two opposing curves the length of the longest piece of rolling stock usually solves the problem.
S curves also occur in rail yards. They often take care of themselves if you’re using #6 or larger turnouts.
Reverse Curves (also called S-curves) A reverse curve is two curves turning in opposite directions, generally not having a tangent track between them.
Reverse curves are undesirable. The problem with the reverse curve in railroad modeling is coupler alignment, and it shows up at its worst on long rolling stock and tighter radius curves. The instant a car is leaving one curve and entering the other, centrifugal forces arc acting in opposite directions on its two ends at the same time.
I spent alot of time trying to use my curve template tools to create the S-curve. Alot of time. It didnt work. I decided it would be easier to use the Ribbonrail track tools I had to create the S-curves in the canyon. I had 5 and 10 inch straight, and 26, 28 and 30 inch radius tools to shape the track and then make a paper template for this portion the the WWSL roadbed.
From the ROW design decision for an 8 inch wide roadway through the canyon, I cut a partial roll of brown paper 8 inches wide to create the cosmetic curve and tangent canyon template.
- On the 8 inch brown paper I laid out the maximum tangent lines at 1 in,, 4in. and 7 inches.
- In the middle of a 36 in. piece of flex track, I placed a 10 in. straight ribbon rail tool.
- On either side of the 10 in. straight tool, I laid a short 28 in. tool, a short 26 in. tool, another short 28 in. tool and a 5 in. straight tool.
- I identifed the mid-line of the 10 in. straight tool at the 4 in. tangent line.
- I adjusted the 3 radius tools on each side inward or outward until the 5 in. straight tools are parallel to the maximum tangent lines previously laid out.
- I then traced along both edges of the tie line, marked the mid line of the straight section, the two points of tangency, the points of curve for each of the radius tools,and the outside point of tangency.
- Once I had the tracing, I cut it from the brown paper and then moved to the styrofoam roadbed and layed out the S-curves along the right of way space.
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