The helix has 6.75 loops and has an approximate 2.05% grade. The initial plans called for a single track but we built the helix wider and accomodated two tracks.

The outer radius is 21.5" and the inner is 20.5". With the two tracks, some redesign has been done to the layout since I want to stay away from two parallel tracks going into and out of the helix.

Testing the up the hill run.
I've had quite a few queries about how the helix was constructed. Well here goes.

Bob Davis was the big help in putting this together. It is made up using 3/8" plywood. We first cut a full circle to use as a template. From that, it was determined that segments which amounted to approximately 1/6" of the circumference would be cut which maximized the total number of cuts we could get from the plywood sheet.
To get the final width, the segments were then run through a band saw. The ends of each segment were cut so that the proper diameter would be obtained when we butt the segments together.
Following that, each end segment was lapped, glued and stapled together.
The uprights are cut from #2 white pine. Each was marked as to where the center of the sandwiched plywood should be. A sheetrock screw was then drilled through the pine into the center of the segment at the upright. Since the two layers of plywood made a 3/4" think segment, only four upright are used as there is plenty of stability - which is what I wanted.

I will be adding some thin cardboard stock around the segment in case there is a derailment. I hope this helps those who asked about the construction and other that might.

The outer loop leaves on the lower level making a turn
to the area under the upper yard. The radius here is 18".
Cardboard has been added to the helix sides to protect against
equipment hitting the floor if and when there is a de-railment.
Here we go around the wall. The board with the blue markings is at a wall corner.
The view is towards the back of the masonite backdrop.
Here we look at the front side of the unpainted masonite.
Another view of the run down to the lower level. This run has a 2% grade.
Here the inner loop begins to exit the helix to the left side of the lower level.

Return to Dispatch