Practical tools for measured work
Model Railroad Helix Calculator & Segment Template
Work out helix grade, turns, track length and footprint, and print a full-size deck segment template.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Centre-line radius of the innermost track. This is the steepest track.
Centre to centre. Check it with the curve clearance calculator.
Top of rail to the underside of the deck above. Use your tallest equipment plus a margin for a hand to reach in.
Underside of the deck to the top of the rail above it.
Width of the subroadbed for one track. For double track this is added to the spacing.
Space between the deck edge and the enclosure or wall.
Enter 0 to skip. Used to find the radius needed.
The template shows one deck segment at full size. Print at 100% or Actual size, join the tiled pages, and check the 25 mm square before cutting.
How it works
Rise per turn is the clearance above the railhead plus the thickness of the deck, roadbed and track on the level above. The gradient is that rise divided by the length of one turn on the inside track, 2 × π × radius.
Footprint is twice the outside radius of the deck plus your edge clearance. On a double-track helix the outer track is longer, so its grade is gentler than the inside track.
Segments: most helixes are built from equal plywood segments so each piece fits on a sheet. The template shows one full-size segment, including its arc and centre line. Each segment climbs the rise per turn divided by the number of segments.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Measurement unit
- Inches
- Inside track radius
- 24
- Tracks in the helix
- Single track
- Track spacing (double)
- 2
- Clearance above the railhead
- 3
- Deck, roadbed and track thickness
- 1.25
- Deck width per track group
- 2
- Edge clearance
- 1
- Segments per turn
- 8
- Total rise needed
- 12
- Target gradient
- 3 %
Primary result: Gradient on the inside track: 2.82 %.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
The grade is a plain rise over run and does not include any compensation for curve drag, which reduces the load a locomotive can pull on a tight curve. Clearance above the railhead must cover your tallest equipment, pantographs and any rerailing hand. Check the segment size against your sheet material before cutting.
Frequently asked questions
Which radius do I enter for a double-track helix?
Enter the inside track radius. The outside track is placed the entered spacing further out, and the deck is widened to cover both.
What clearance should I use?
Use the height of your tallest car or locomotive above the railhead, then add enough room to reach in and clear a derailment.
Related tools
Grade Calculator
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Easement Template
Print a full-size spiral easement and curve template for model railroad track, with the exact offset from the tangent.
Curve Clearance
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