Practical tools for measured work
Printable Curve Template Generator
Print a full-size circular curve template for one or two tracks, with chord, sagitta and radial tick marks.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Centre-line radius of the innermost track.
Width drawn around each track.
Centre to centre. Use the curve clearance calculator for long cars.
Radial guide lines. Enter 0 for none.
Print at 100% or Actual size, join the tiled pages, and check the 25 mm square. Trace the blue centre line onto the subroadbed.
How it works
Geometry: the template is a true circular arc. Arc length is radius × angle in radians. The chord is 2 × R × sin(angle ÷ 2) and the sagitta, the gap between the chord and the arc, is R × (1 − cos(angle ÷ 2)). The chord and sagitta let you mark the curve with a straight edge and a tape if you prefer.
Double track: the second track is placed on a concentric arc the entered spacing further out, so both tracks share one centre and stay parallel.
Printing: the pages tile at full size. Set the printer to 100% or Actual size, never Fit to page, then check the 25 mm square before using the template.
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
- Scale
- HO (1:87.1)
- Curve radius
- 24
- Arc angle
- 90 °
- Roadbed or template width
- 1.5
- Tracks
- Single track
- Track spacing (double)
- 2
- Tick marks every
- 15 °
Primary result: Arc length (inside track): 37.699 in.
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 template is a plain circular arc with no easement, and templates that need more than 80 printed pages are not offered. For large radii, mark the curve with a trammel or a flexible batten using the chord and sagitta. Rail and roadbed lines are nominal and do not replace the manufacturer's track template for turnouts.
Frequently asked questions
Can I print curves larger than a table?
Yes, up to the page limit. The pages are tiled and numbered so they can be joined edge to edge. For very large radii a trammel or batten is often easier.
Should the curve have an easement?
Tighter curves usually look and run better with easements. Use the spiral easement template to draw the transition into the same radius.
Related tools
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