I had a helix installed, but it was only temporary to connect the end of track on the first level back to the staging yard. [There is about a 5 inch difference from the east end of level one and the west end.] What I need for the finished layout, is actually two helices. I need one that connects the west end of level one to the east end of level two, and another to connect the top currently at the west end of level two back to the west staging yard
As I mentioned in my post of February 12, 2010, while I was at the Hartford Convention, I attended a clinic by Bob Hamm on Helix construction. Bob uses threaded rod and laminated plywood roadbed to support his helices. I had done that in my earlier temporary helix. The big difference in construction was the subroadbed on my temporary helix was a polygon formed by straight sections with an angle cut allowing for a complete circle when laminated together. Bob does some calculations and then uses what he calls "banana cuts". The outer radius of the roadbed is also used for the inner radius, moving the center of the circle so the inside off-set outer radius curve lines up with the expected inner radius at the ends of 90 degree sections. This results in a roadbed segment that is wider in the center than on the ends and does, sort-of, have a banana shape. I cut the sections from 1/8" luan plywood, "ganging" about 4 or 5 together to cut them. I laminating them together with about a 30% off-set so the joints are not over previous joints. I had scribed the curves in the seal on my driveway and just assembled the helix subroadbed on the ground. As I continued around, I placed waxed paper between the levels to keep them separated. The inside "top-to-bottom" helix is about 6 1/2 turns. This became somewhat complicated but I just kept laying more wax paper and kept laminating until I had enough turns.
The real complication is that the outer helix that goes from level one to level two, while only 2 1/2 turns, actually turns the opposite direction. That is the inside one rises in a counter-clockwise direction when viewed from the top. The outside helix rises in a clockwise direction. I have jokingly called this counter rotational. the complication comes when you put in the threaded rods and sub-roadbed supports. The helices cross each other's plane twice per rotation so reaching through from the inside to the outside is complex. This may be necessary if, or maybe I should say when, there are derailments in the helix. Eventually, access will be limited to the inside only, once scenery hides the helices.
Here are a few photos of marking and cutting the banana curves.
Here are photos of laminating the helices on the driveway.
And here are the completed laminated helices in position with a few of the threaded rods in place but before the helices were erected.
I will post some more soon on the actual assembly of the helices to make them usable.