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| THE CRAFT Definition and Brief History of Ornamental Turning Plain turning is where a transverse section through
any part of the work comprises a plain circle. Ornamental or Complex turning is done on a lathe with
attachments which convert that plain circular section to variants of outline;
these range from a simple series of cuts taken at intervals around the
work (so producing grooves or bumps on the surface) to non-circular movements
whereby the whole of the circular shape is removed to give a completely
different form. Such shapes are achieved by various means, the principal ones
being:- - Cutting with a fixed or revolving cutter while the work
is rotated on a non-radial path, e.g.- eccentrically, elliptically,
epicyclically or, following a path determined by a template or reciprocating
device; - Cutting with a revolving cutter while the work remains
static, then partially rotating the work (using an indexing device) so as to produce a series
of cuts at intervals around the cylinder or surface; - Cutting with a fixed or revolving cutter while the work
is rotated on a radial or non-radial path and the cutting apparatus follows a linear, circular or
non-circular motion, the two motions being synchronised by gearing; Ornamental turning is believed to have originated in
Bavaria in the latter part of the 15th century when it consisted
mostly of rose-work, being done by using a cam or template (called a rosette)
mounted on the lathe spindle and allowing the headstock to rock under tension of
a spring or weight, to follow the contour on the edge of the rosette: also the
spindle was allowed to slide to and fro endwise under tension of another spring
to follow the contour on the face of the rosette.
Thus, as the work was rotated it rocked and traversed so that the cutting
tool produced wavy lines upon the surface.
Cutting tools were generally hand-held or clamped before the end of the
18th century, the slide-rest, although invented c.1480, was not in general use
until much later. It is clear from surviving examples of their work that the
skill of the early turners was highly developed. In response to growing interest by wealthy and great
patrons, including several of the royal families of Europe, two great works on
the art and science of turning were published in France: “L’Art du Tourneur”
by Plumier (1701) and “Manual de Tourner” by Bergeron (1792).
Meanwhile, turning technology was being developed in England where the
practice of arresting the work from point to point (by a division plate) and
applying a revolving cutter (held in an improved slide-rest) was employed.
By the beginning of the 19th century John Jacob Holtzapffel
had established his workshop in London and built a reputation as a maker of
high-class lathes and tools. Many
of his customers were among the monarchs and nobility of Europe.
Other engineers copied or varied his designs and England became the world
centre for ornamental turning. The
Holtzapffel firm continued to make lathes until 1927 by which time they had
produced a total of 2557, serially numbered, many of which were equipped for
ornamental turning. Relatively few of these mechanical marvels survive today and hardly any are complete with all their original accessories. However, the hobby is still kept alive by a small band of enthusiasts, notably the Society of Ornamental Turners, based in England but with members world-wide, who seek to develop the knowledge of O.T. and to restore, maintain and use the old equipment or, adapt modern lathes for ornamental turning. Some are even bringing the hobby up-to-date by building computer-controlled O.T. lathes. The greatest work on ornamental turning is “Turning
and Mechanical Manipulation” by Charles & John Jacob Holtzapffel (5 vols.
1843 - 1897). Volume 5, entitled
“The Principles and Practice of Ornamental or Complex Turning” is considered
to be the ‘bible’ of O.T. but there is much related information in the other
volumes. Other useful books
include: “Ornamental Turning” by J H Evans (1903-4), “The Lathe & Its
Uses” by J Lukin and
“Ornamental Turning” by T D Walshaw (1990).
Reprints of all these books are usually obtainable. The hobby of ornamental turning declined rapidly
following the invention of the motor-car which, by the end of the First World
War, had become the fashionable pastime of the mechanically-minded amateur. The Society of Ornamental Turners
was formed in 1948 with the object to
encourage, develop and promote the study and practice of the art and science of
Ornamental Turning. Its members
meet quarterly in London to display examples of their work, share their
experiences and attend a lecture or demonstration.
Seminars and outings to places of interest are also arranged.
A Bulletin containing articles on all aspects of O.T. and news of the
Society is published half-yearly in March and September and a Newsletter in July
and December. Competitions are held annually for ornamental turning, plain
turning, making equipment, displays at meetings, contributions to the Bulletin
and for advancing the knowledge of the art. Over many years a close association has been formed
with the Worshipful Company of Turners and several members of the Society are
Freemen or Liverymen of the Worshipful Company. From time to time the Worshipful Company holds competitions
which include categories open to members of the Society. Ornamental Lathes and their Accessories This is an introductory treatise which includes a brief history of ornamental turning, pictures of lathes and their accessories with notes on their uses and examples of work. It is divided into 10 parts each of which may be accessed by clicking on the links below: lathes1.pdf lathes2.pdf lathes3.pdf lathes4.pdf lathes5.pdf lathes6.pdf lathes6.pdf lathes8.pdf lathes9.pdf lathes10.pdf To preserve the relationship between the text and the pictures in this publication
they are offered in Adobe Acrobat® format. The size each part is approximately
250Kb.
If you have difficulty accessing from the links above this treatise may also be accessed on the website of the Society of Ornamental Turners - www.the-sot.com Techniques of Ornamental Turning [click here for current techniques] The Heart-shaped Cam for generating Rosettes Heart-shaped cams are used on the Geometric
Slide-rest to generate attractive rose-shaped patterns; rotating the cam several
times to one rotation of the lathe spindle produces the pattern designated by
Holtzapffel as 'F'. Holtzapffel & Co., provided rosettes of several counts, such as: F3, F4, F5, F6, F8. The picture opposite shows a pattern cut by a multiple of 3 hearts, or 'F3'; the effect of spreading out the heart shape in this way gives the appearance of a series of 'Cupid's bows'. This type of cam may also be used on the Geometric Slide-rest to generate rosettes for 'Rocking Headstock' type rose engines. The writer has made heart-shaped cams in plastic by mounting the blank disc on the Eccentric Chuck, cutting 3 curves of different radius on each side, then smoothing the joins by filing and finishing with fine abrasive papers. However, this method is not truly satisfactory. The curves are determined by trial and error after marking out the blank in the manner shown in the drawing below:
The curve on one side of the heart shape is like a logarithmic curve or a Fibonacci spiral. Surely, there must be a simple mechanical means of generating one side of the heart shape, then reversing the process to generate the other side. Here are two theories that might give a clue to how this could be done. If any reader knows the answer or if any reader would care to experiment with these and any other theories, please send an email of your findings to ornamental.turning[at]talktalk.net. Theory #1. If a long rod or beam was fixed across the face of a gear wheel such that, as the lathe spindle rotates the gear also rotates and the rod, starting vertical, swings round towards horizontal, or vice versa. If the top end of a second rod was joined by a swivel joint to the top of the first rod and the bottom end of the second rod was joined by a swivel joint to a horizontal slide, surely the slide would accelerate and decelerate as the relative angles of the rods changed? If this works it should be possible, by changing the relative lengths of the rods and the ratio of the gear to the lathe spindle, to generate a curve suitable for one side of a heart? Theory #2. If, instead of a rod, one were to fix an oval cam to the gear wheel and a rubber to the slide, then as the cam rotates its eccentricity would cause the slide to accelerate then decelerate relative to the rotation of the lathe spindle? If this works it should be possible, by changing the relative sizes of the major and minor axes of the oval and the ratio of the gear to the lathe spindle, to generate a curve suitable for one side of a heart? Or, is there a better way? - If you know - please share that knowledge.
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Last modified: May 02, 2008 |
