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Location: St. George, Utah, United States

Jan 25, 2009

12 The Helix

The first big (and we mean BIG) project was to construct a helix for the railroad.

If you are a model railroader you know what a helix is and its purpose. For the rest of you that may read this blog let's explain a bit.

The Ascape Tennsion & Sulphur Gulch Railroad is a bit like a stage play. There is the main stage where the action of the play takes place and then there are the wings or staging area where actors wait until it is their turn to appear on the scene and play their parts. Well a model railroad is similar. On the part of the railroad which the visitor sees, trains enter to deliver their freight cars to various industries and then leave the scene on their way to some distant unseen destination. A train enters at one location, travels across the visible part of the railroad, and then exits at the other end of the visible portion of the railroad.

Where do the trains come from and where do they go? Like a stage the model railroad has a staging area where the trains wait until it is their turn to enter the seen railroad and play their part, that is make their trip, deliver their goods or passengers, and then exit back to the staging area.

On the AT&SG the staging area is at a lower level under the town of Ascape. This staging area consists of a large rail yard where trains and rolling stock (freight cars and locomotives) can sit waiting for their turn to run on the railroad. On the far end of this staging area on the AT&SG there is a loop that can be used for turning trains. So when a train enters the staging area it goes around the loop and then into a siding in the yard ready for its next turn to enter the railroad.

On the other end of the staging yard is the helix. A helix is a spiral of track that allows trains to raise from the lower staging yard to the level of the main line of the railroad. The staging area of the AT&SG is about 10 inches below the main part of the railroad hidden under the scenery (or what will be scenery). When a train is ready to enter the railroad it enters the helix at one end of the yard travels around the spiral about 4 times until it is at a level where it can enter the main line of the railroad.

The journey across the AT&SG takes a train over the railroad on a lower level and then returns at a higher level back over the railroad. After completing its journey is enters the helix at a higher level and returns to the staging area having completed its work.

The remainder of this post is for those who are interested in how the helix was constructed. For the casual reader you may want to exit at this point.

Constructing the helix was an engineering challenge for the construction crew of the AT&SG. The challenge is a very smooth surface, a minimum grade sufficient to raise the trains to the appropriate level, and sufficient clearance between levels so that the trains have space to travel.

The construction crew decided to construct the helix from 3/8" plywood. Two complete circles of plywood 5 inches wide were cut from each of two 4x8 sheets of plywood. The outside diameter of each circle is 24 inches making the track radius 22 1/2 inches ( a rather tight radius, but since the AT&SG is circa 1937 most of the equipment is small with short 40 foot cars. There are a couple of 60 foot passenger cars but they can navigate these curves as well.) Using the remainder of the plywood 3 more circles were pieced together in sections.

The circles were then cut at one point to enable a spirial. The second section was attached to the first section using 1/4 in dowel pins with a piece of 1/8 Masonite glued to the underside to provide more stability at the joints. When all the joints were completed there was a spiral of 6 1/2 loops of continuous plywood ramp. This spiral of plywood loops was then secured to a framework base that raises the bottom of the helix to match the staging yard.

The next engineering challenge was how to support the spiral of plywood loops. The construction crew decided to use threaded rods and secure the loops with a nut and washer below and above each level. The original intent was to drill the holes in the plywood loops themselves but keeping the holes in line turned out to exceed the capabilities of the construction crew so an alternative method was devised. The posts were placed outside the plywood loops and a thin piece of fir (left over from ripping 2x4 studs for legs) were used under the plywood loops as shown in the illustration.

The tedious part was threading each of the 12 rods with 12 nuts and washers inserted between the supports. When the rods were all finally threaded with a nut and washer below and above each support the rods were secured into the platform framework to hold them securely in place.

The next step was to carefully raise each support to the correct level to promote a smooth upward spiral with a grade of 3% and a clearance between levels of 4 inches. When each support was at the correct level the nuts were secured both top and bottom of each support. When all was secured, the elevation checked, and the clearance checked then the plywood spirals were hot glued to the supports to provide stability.

When all was completed the helix was secure, stable, and ready for track and being connected to the track from staging and from the main line. It was critical to complete the helix before installing roadbed for either the staging yard of the main line. That is next. Check back for progress on this next phase of this project.


OpenID Roger said...

I love being able to check on the progress of the Ascape, Tennsion, & Sulphur Gulch Railroad from afar. The combination of engineering and artistry is remarkable. We look forward to checking progress in person before too long ...

Blogger tkcollette said...

I never knew the complexity of putting together a large scale HO train set! This is quite the remarkable endeavor! Incredible!


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