Yet Another Helix Design
I needed a helix to get between levels on my layout but I had other requirements besides
diameter and grade. The helix is at the end of a peninsula and I wanted to have track and
scenery on both levels on the outside of the helix. This meant the helix needed to support
a smooth backdrop as well as upper foam benchwork, track and scenery. Finally, splice
plates weren’t feasible because of the grade and the required vertical spacing.
The track radius in the helix 28” with a rise of 3.75” between laps (2.13%). I’m using ½”
plywood for the sub-roadbed, giving 3 ¼” vertical clearance. I’m not using any other
roadbed because of the tight clearance. I’m not concerned about reducing noise in the
helix since that will give operators a clue that the train is still moving. The track is glued
directly to the plywood with Woodland Scenics Foam Tack glue.
Since I wanted a smooth surface on he outside of the helix, I cut circular segments from
plywood and used a glued lap joint to join the segments. I used Cadrail to figure how
many segments I could squeeze in then laid out the pattern on plywood sheets. Each
segment was 5 ½” wide to allow clearance for vertical spacers and range in length from
225 degrees of a circle to fairly short segments. I was able to get all five laps of the helix
from only two 4’x8’ sheets of plywood.
To join them I used a router to mill a 2” wide notch on each end, exactly ½ the depth of
the plywood. I was surprised how much sawdust you can generate doing this! Once all
the notches were milled, I assembled multiple short segments together to form larger
segments about the same size as the biggest pieces. I used Tite-Bond III to glue the joints.
The smaller segments were sandwiched between two larger segments to make sure they
were nicely circular. The joints were clamped overnight to allow the glue to develop full
strength. . Aluminum foil was used between layers to prevent the sandwich from gluing
Note: I did a small test case prior to assembling all the pieces to see how strong the joints
were. After setting overnight the joint itself was stronger than the plywood. When I tried
to break the joint, the plywood delaminated before the joint gave way. Tite-Bond III is
The helix was assembled a lap at a time. I screwed down a segment to spacers on the
segment below using thin washers as shims to ensure the helix had a very slight super
elevation. All the track joints are soldered to make sure no kinks develop. Next I glued
the track in place and used masking tape to hold it in alignment.
I placed the next segment in position at this time and glued spacers on top of it. The
vertical spacers are staggered so I could glue and screw them from below and above. The
spacers also hold the shelf brackets for the upper foam benchwork as well as ¾” standoffs
for the backdrop.
After allowing the Foam Tack and Tire-Bond to set overnight, I lifted off the next
segment and screwed the spacers on from below for strength. The holes for the screws
were slightly countersunk so the screw heads would not cause alignment problems.
The track masking tape was then removed and the track was wired and tested. I ran bare
copper 12 gauge wire on both the inside and outside of the helix track to connect DCC
feeder wires. After ensuring the track was electrically and mechanically perfect, the next
segment was begun.
The final helix section has an increasing radius to allow the track to transition to the foam
benchwork on the outside upper level. The grade of this section levels off to meet the
Finally, the shelf brackets and backdrop supports were added to the vertical spacers. The
backdrop supports are ¾” thick so that most of the shelf bracket did not protrude through
the back drop. Notches were cut in the Masonite backdrop to clear the brackets with
drywall tape and spackle covering most of the bracket that was visible.
The finished helix is very strong and stable. It’s a shame it’s hidden by the backdrop.
People can still climb into the middle to see all the construction if they desire. If I ever
decide to have a dispatcher, the center of the helix will make a nice four foot diameter
office hidden from the view of the operators.
Director of Everything, The New Great Western Railway
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