This clinic outlines a method for building an open center helix that has been featured in Model Railroader.
[Editor's Note: What is a helix? A helix is a climbing or descending curve of track which turns around an axis like a corkscrew. They are sometimes used on multilevel layouts to allow trains to go from one level to another in a relatively small space.]
Parts and Tools List
| Description | Note |
|---|---|
| Threaded rod | 5/16" preferred, but may be 1/4" or 3/8" |
| Appropriate size washers and nuts | (for the threaded rod) |
| Base brackets | (may be metal angle or wood) |
| Support brackets | hardwood preferred |
| Plywood for sub-roadbed | 4-ply or more |
| Roadbed material | 1/8" thick shelf cork or other desired material |
| Track | |
| Wrenches | |
| Wood glue | Weldbond or Elmers carpenter type |
| Clamps | Lots! |
Construction
Initially, the system will appear unstable - rods will flop about a bit. By the time the second level is in place, rods will be firm and the entire system will be solid. By leaving the rods sitting on the base brackets, the entire helix may be lifted off should it be necessary to relocate. My two track helix has 4 loops and contains close to 100 feet of track on a minimum 26" radius. Power is fed to the rails on opposite sides. I used 7 rods and they're spaced from 18" to 36" apart.
A helix can be sized to produce a desired grade - thinner materials produce a lower grade, or as in my case, I had a defined area I could use, so the grade is what it needs to be to maintain the spacing between levels.
- Lay out approach track to determine the start point of the helix structure.
- Determine maximum radius if working in existing open space benchwork; or calculate the space required to achieve the desired grade and build appropriate open space benchwork. Cut sub-roadbed segments from plywood.
- Find the center of the helix to keep helix elements properly aligned. Lay out segments on sub-roadbed material and cut pieces.
- With segments laid in place, determine locations of base supports around the outside of the helix. Drill holes in base supports and install in desired locations - maximum distance is probably about 3 feet, but 2 is better. Keeping the brackets outside the helix will provide unrestricted acces to the track for cleaning or other maintenance from the inside.
- Run a nut onto the threaded rod, add a washer and another nut. Put a washer on the base support and drop rod in place. Anchoring nut is not needed - just let it sit there.
- Cut a support bracket sized to reach under the sub-roadbed - first level brackets need not be beveled. Drill clearance hole in bracket, place a washer onto the rod, drop the bracket onto rod and add another washer and nut. When nut reaches bracket, tighten finger tight.
- Apply glue and clamp sub-roadbed to bracket(s) and clamp 'til dry. Sub-roadbed segments should bridge two brackets and can be glued end to end using scrap pieces of sub-roadbed or other material to maintain integrity between segments.
- Remove clamps, apply sub-roadbed and lay track.
- Proceed around helix adding support brackets (bevel cut as indicated in pictures) with nuts and washers, segments, roadbed and track. Tighten nuts against brackets - threaded rod allows for fine adjustment. Get into the helix and eyeball it.
- Use NMRA Track Gage to determine spacing between levels, setting gage on the track and support bracket spaced to touch top of gage.
- Continue to desired end-point.
- Complete wiring of track according to your methodology. You may want to consider installing feeder wires as you build the helix, and then connect them to appropriate bus wires.
Conclusion
Using this approach to helix construction allows any errors to be easily corrected by adjusting the brackets up or down of the rod. Sitting in the middle and eyeballing is a good way to make adjustments. When happy, tighten nuts against brackets. Open center permits access for cleaning.
Fred Wintsch
Presented January 9, 2010