A Strong Foundation
First we built a c-channel strut framework, with two sections in back that are bolted into the floor and ceiling. Two additional struts in the front are bolted only to the floor. A horizontal box frame was bolted to both sets of vertical struts and carefully leveled. This is an important step as you really want a level base for the helix. A 3/4″ plywood tabletop was then built that rests on the horizontal framework:
A reverse loop around loop will be laid on the table, which also serves to anchor the base of the helix to the lower level of the benchwork.
In the photo below, the CADRail design documents are being validated against the as-built table. The strut nearest the computer and the other gold colored strut on its right are the short struts. The two silver colored struts are anchored to the ceiling as well as the floor. The edge of the innermost horizontal struts can be seen on the inner edge of the table:
Two cross-struts are placed on the long axis of the table and then a box frame (like a picture frame, only out of C channel) is built on top of them. The box frame is bolted both to the base horizontal struts and to each other. 3/4″ plywood is bolted to the box frame to make the table. From underneath, you can clearly see that this structure is solid:
Holes were drilled in the plywood to position the threaded rods that will be used to suspend the helix and the rods are bolted into place. Each rod is held with two nuts below the plywood and one above. Washers are used everywhere to make sure things are tight and don’t move around.
Some quick work with the jigsaw and we have a nice rounded table top with the threaded rods extending upward:
Too much fun with Plywood
We tried to save some money by carefully cutting as many sections of helix as possible from each 4’x8′ sheet of 3/8″ plywood. We had several different shapes of plywood because our helix isn’t a circle. The idea was to overlap the plywood in two layers so that the joints of one layer would always overlay unjointed plywood in the other. This means that unique pieces of plywood were cut and then glued up in a very specific order.
Saving money by cutting a lot of small pieces of plywood was a mistake!We probably only saved a few of sheets of plywood, but it took four many multi-hour work sessions over the course of SIX weeks to assemble the helix. It also took a long time to glue up all the small sections in pairs and then glue up the pairs into bigger sections and so on.
If we had it to do over again, we probably would have wasted some wood, and saved at least a month of construction time.
Here you can see one pair of pieces that have been clued up and are now clamped waiting for the glue to cook. Not only was the work tedious, but we were often held up because we ran short on clamps!
Once several small sections were glued together, holes were drilled in them and they were placed on the threaded rods and roughly positioned. Each time a new section was added, the overlapping area had to be glued and clamped. Here you can see the first and second sections in place and being glued up.
This photo shows a detail of the bolt and plywood arrangement. Homasote is glued to the plywood and a double track mainline is laid on the homasote. Each layer of plywood has nuts and washers above and below it. The lower nut is used to set the height of the plywood while the upper one is tightened to keep the assembly from moving. Also visible in this picture is the wire bundle that circles the inside of the helix carrying DCC power. On the helix we have a power drop on each piece of flex track.
Below is another view of the first and second sections being glued together in place. Notice how the laminate of the upper half of the second section is not complete as the overlapping plate will be on the third section and so forth.
Eventually we got tired of doing one section a week, so we glued up three quarters of a turn of the helix. We also solved our clamp shortage by actually using drywall screws as temporary clamps — you can see the last layer of the helix resting against the wall behind what has been built up.
Here you can see the entire helix, from above, except the last 3/4 turn, which is still sitting on the wall, curing. Notice the level on the second layer. We have a member who owns a digital level that will read out the grade in percent. This level came in very handy when leveling the helix, which is at an average of 1.9% slope.
The helix is slightly super-elevated, although not as much so as the glue bottles below make it appear. In the corner on the right you can see the drill press we used for drilling holes in the plywood section.
Here Dave and Dave work on leveling the helix. Two levels are used. The digital level is placed along the direction of the helix and rise and run is read from it. A smaller bubble level is placed across the direction of the helix and superelevation is set using it. Once all the turns of the helix were in place, the exercise of leveling it went surprisingly quickly.
We’re an operations club, so as soon as there was track on the helix, we inserted a shoo-fly on the upper level and ran trains up and down the helix, even though the ramp at the bottom wasn’t there yet. In this view you can see the straight sections. Notice that on each straight section there are re-railers. It’s an interesting insurance policy and we’ll have to see how it works.
Here is another view of the helix, showing a train near the top. We kept the fan in the middle because it gets hot working in there! Eventually, we’ll hide the helix behind a curtain, but it will always be easy to get at for re-railing if necessary and possible, although not trivial to get at the inside for any maintainance.
We have the connection from the top of the helix to the upper level of the benchwork done, but still need the ramp that will connect the bottom of the helix to the lower level. To reduce the number of turns and grade necessary, we extended a ramp from the bottom of the helix along one arm of the benchwork.