Almost all the pieces I sell are 'plain' turning, made by applying a more or less stationary cutting tool to the spinning wood, making objects that are circular in cross section.
If, instead, the cutter and workpiece move relative to each other in a precisely controlled way, the result need not be circular in cross section. A pattern or shape is made on the wood. For example, six cuts spaced around the workpiece could leave it with a hexagonal cross section. This is 'complex' turning, and it is a very different craft. It is much more dependent on specialised tools and equipment than is plain turning. It is often known as 'ornamental' turning, not because it makes ornaments, but because it applies ornamentation to surfaces.
Great ingenuity has been devoted to developing the equipment. Originating in the late 15th century, the craft later came to be primarily a rich man's hobby. The kit was beautifully made, and priced accordingly. Surviving examples, such as the lathes made by Holtzapffel, are now highly sought after.
Ornamental turning requires a special lathe, tools, chucks and elaborate gearing systems to control the relative motion of the cutting tool and the workpiece. Modern set-ups may be computer controlled. This equipment allows complex, coordinated motions of tool and workpiece, generating ornamentation that sometimes can be baffling to see.
These motions may be any combination of eccentric, epicyclic, radial, elliptical, linear or reciprocating, or they may follow an irregular template or one with a pattern. The cutting tool may move, or the workpiece, or both simultaneously. Cuts are accurately indexed so they start and stop in exactly the right position.
A variety of materials are used for ornamental turning, including wood, ivory, bone and some plastics. The materials must cut very cleanly, as sanding is rarely possible on this type of work. The finish is that left by the tool. This means that few wood species are suitable. Boxwood and African blackwood are the ones most often used. They are hard and fine grained and respond well to cutting tools, leaving a polished surface. The cutter must be extremely sharp, and special equipment is used for sharpening too. Certainly the normal standard of sharpness required for plain turning would not do for complex turning.
Above is a bowl in teak that I made using the principles of ornamental turning. I used a rotating fly cutter with the bowl stationary, but indexed round a few degrees between cuts to form overlapping circles, part of which were then removed by plain turning. Teak is quite coarse-grained and far from ideal for this work. A real ornamental turner would think it very crude! The box below was made in the same way, but the circles are complete and begin to show how complex patterns can be built up. I did not make this box.
The vase of flowers below (not my work!) is a masterpiece of OT. All the numerous parts were machined using complex turning equipment.
An example of an ornamental lathe made by Evans. Note the drum on the overhead holder. A cord wrapped round this, running over jockey wheels, is used to drive rotating cutters.
Below is a Holtzapffel lathe.
Another example of an OT lathe. The cords from the overhead drum can be seen.
Below is an example of a rose engine. Its shaped wheels are templates for an oscillating motion.