At a recent Wednesday meeting the demonstrator, Lloyd Walton, showed how to insert a spiral of copper wire as decoration around a turned article, in this case a drop ear-ring. Lloyd did a great job of saw-cutting the groove for the wire "by eye" which is no mean feat as the result was quite spectacular.
In the trade of pattern making it is often necessary to mark out helical lines on cylindrical work when making patterns for worm wheels, conveyor screws or marine propellers, usually to precise dimensions and specifications.
Here is one way to do it.
1 Turn the required cylinder.
2 Cut a paper template which will wrap neatly around the cylinder and draw a diagonal line.
3 Wrap the paper template around the cylinder and the diagonal line will accurately create a helical line or "helix" on the surface
If you want a "double start" helix, ie .two helical lines of the same pitch on the cylinder, mark out the template like this.
Wrapped around the cylinder, this creates two equi-spaced helices.
Alternatively, you could use the original template and index it around the cylinder to mark as many helices as required.
In these examples the helices shown are "right handed. For left hand helices mark the diagonal ines in the opposite direction. Note that the "hand' of the template cannot be altered by changing the template end for end.
The method shown could be used for carving barley-corn twists on turned work.
There is nothing new about all this, the Greek mathematician Archimedes discovered it in about 200 BC when he invented the famous "Archimedean Screw".