Handrailing
Also called: handrail wreath, tangent handrailing
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Handrailing is the geometric problem of shaping a continuous rail that twists and rises to follow a stair, so that it is cut correctly at every point along its curve. Several named methods exist for working out those cuts.
Named methods
Square Cut and Tangent are two such methods, and Falling Line a third; Ellis combined all three into a single approach of his own, though this combination is his own way of working rather than standard practice across the trade. A separate approach, the normal sections method, is credited to Mowat for its fuller treatment.
Fixing the cutting plane
One handrailing method fixes the plane of section, the flat plane a cut is made along, by using a triangular prism. It relies on a plain fact of geometry: a triangle's side lengths can only be arranged into one shape, so a prism built to those lengths pins the cutting plane down without ambiguity.