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The Ornamental Turning Lathe
The ornamental-turning lathe begins as a simple wood- turning lathe. It differs in the wealth of attachments that make possible decorative embellishment not feasible with an ordinary lathe. The primary attachments are an indexing plate and a slide rest. The indexing plate, on the front of the pulley, contains rows of holes into which a fixed pin can be inserted to stabilize the lathe mandrel in a given position and keep the work from turning. This allows the turner to make cuts in the precise locations he or she chooses. The slide rest holds the cutting tool in position and provides a mechanical means of moving it from one position to another. In addition to these two attachments, numerous auxiliary apparatuses provide the means for making the ornamental cuts. All of these attachments are discussed in more detail later in this chapter.
Four basic types of motion are possible with an ornamental lathe:
A fifth type of motion may be obtained with a rose engine lathe, which has a rocking headstock.
The mandrels of the ornamental lathe are of hardened steel and run in hardened steel bearings. There are no ball or roller bearings, as are found in modern plain-turning lathes. Norman Tweddle commented on this anachronism, saying, "Provided they are kept freely lubricated they seem to be everlasting. No provision is made for taking up wear. The thrust must be carefully adjusted so that the mandrel turns easily by hand without any end shake whatever. On being properly adjusted it should be possible to spin the stepped pulley for at least a dozen revolutions on being pulled round by hand."
Power for the ornamental lathe is provided by a foot treadle operated from beneath. The treadle activates a flywheel, which in turn activates the belts that extend from the flywheel to the stepped pulley in the headstock as well as to the overhead drive. The modern ornamental turner invariably motorizes his lathe, creating problems that are not found in the foot-treadled lathes. The higher and more sustained speeds at which the motorized lathe can be run create a problem in oiling the main bearings. Because the lathe was built to run at slow speeds, only the amount of oil needed to run at these speeds reaches the main bearings. At faster speeds, too little oil reaches the bearings, and they freeze. This problem can be solved with the installation of oil drip cups. I learned this the hard way when the main bearing in my headstock froze. Fortunately I had a friend who was an expert toolmaker, and he was able to unfreeze the bearing, repolish it, and install an oil drip cup that solved the problem.
Types of Ornamental Lathes
One of the earliest ornamental lathes was described by Joseph Moxon in his 1703 book Mechanick Exercises or the Doctrine of Handy-Works. This, the swash plate lathe, produced many eccentric shapes. The swash plate lathe, can be seen only in museums, but other lathes, described below, are all used by turners today.
SIMPLE ORNAMENTAL LATHE. This lathe has a nontraversing headstock mandrel that carries the chucks that hold the work just as an ordinary lathe does. With attachments, it can do all the ornamental cutting actions the average turner may need. It cannot cut screw threads.
SCREW-CUTTING ORNAMENTAL LATHE. This lathe has a headstock with a traversing mandrel. The mandrel is activated laterally through the bearings by means of screw guides, which provide for the pitch of the threads to be cut. Most Holzapffel lathes were of the screw-cutting type.
Screw threads can also be cut on the simple ornamental lathe by adding a spiral apparatus, which consists of a gear train that connects the mandrel to the end of the slide rest. It should be noted that the pitch of the Holtzapffel thread on the nose of the mandrel and in the chucks that fit on the nose are not of the standard pitch used today. Rather, pitch is based on the Strasbourg inch of Holtzapffel's day, 9.45 threads to the inch. The set of wheels that make up the spiral apparatus contains wheels that provide 9.45 threads to the inch.
ROSE ENGINE LATHE. The rose engine lathe exemplifies the epitome of the ornamental-lathemaking skill. The following definition of rose engine is taken from volume 30 of the Cyclopaedia of Abraham Rees, London, 1819:
Rose Engine, Rose Lathe, or Figure Lathe, in the Mechanic Arts, is a machine used for turning any articles in wood, ivory or metal, in the same manner as a common lathe, but it has additional parts, by which the surface of the subject which has been turned, can afterwards be engraved with a great variety of patterns of curved lines, which, in general, are denominated from the French rosette, from a slight general resemblance which they have to a full-blown rose, and hence the machine is called a rose engine.
The Rose Engine Lathe (as we prefer to name it), therefore, is a tool having the main characteristics of an ordinary lathe and in addition a device or devices for reciprocating the headstock both to and from the operator as well as longitudinally in line with the bed of the lathe, either one movement at a time or both together.
The British Science Museum has records of rose engine lathes made as early as 1740 by a German shop. Hulot & Fils made one in 1768, and another French rose engine was made in about 1800. Holtzapffel made improved versions of the rose engines, but only twenty were made by his company.
Norman Tweddle owned a Holtzapffel rose engine lathe and used it extensively, with great skill. A note in the S.O.T. Bulletin stated that he produced work "deeply cut and in appearance very much akin to the daintiest flowers, the rose, the violet, the daisy, the four leaf clover, the shamrock, the fine tracery of maidenfern and even the butterfly which designs, repeated around the edge of a plate, made a perfect enrichment of the pattern."
Tweddle's rose engine lathe was Holtzapffel #16, made in 1797. At the time of this writing, it is in the possession of Geoffrey Roberts of Roxborough, Massachusetts. The last true rose engine made by Holtzapffel is in the possession of Warren Green Ogden, Jr., of North Andover, Massachussetts. It is reputed to be the finest such lathe ever made by Holtzapffel. It is #1636 and was first sold on December 20, 1838.
OTHER ORNAMENT LATHES. Other types of ornamental-turning lathes were rarely made, mostly on special order. One was the medallioncopying lathe, which copied in bas-relief a previously made master medallion that served as a template. Others were based on the lathes described above but were fitted with special apparatuses for special purposes. Some of these were made on order, but most were made experimentally by machinists and toolmakers and were never offered in the marketplace. Those that still exist are collector's items.
Basic Attachments to the Ornamental Lathe
No single attachment converts an ordinary lathe into an ornamental lathe, and it is difficult to discuss them in any sensible order of priority. The slide rest is probably the most important in terms of being able to cut even the most basic ornamental patterns, however, and so it is discussed first.
SLIDE REST. All metalworking lathes have slide rests, while few ordinary woodworking lathes have them. The slide rest, a device that fits on the lathe bearers, can be moved laterally from left to right to any desired position. It supports the cutting tools at the desired angle to the work. The slide rest can move the cutting tools back and forth across the bearers at any angle up to 90 degrees to the bearers. The tool rest on an ordinary woodworking lathe is merely a stationary metal rest on which the cutting tool or chisel is supported.
The slide rest carries a receptacle that holds the cutters. This receptacle or tool box, as it is commonly known, is activated by a lead screw, which extends the working length of the slide rest. This arrangement permits the slide rest to be maintained in a fixed position on the bearers while the cutter is moved laterally along the length of the lead screw. These movements are basic to all metalworking lathes.
The slide rest on the ornamental lathe is similar in principle to that of the metalworking lathe except that it is lighter in construction and is more flexible. It is not called on to do the heavy cutting that is common to metalworking and therefore can be adjusted to lighter types of work that are performed in the delicate cutting operations of ornamental turnery. My Holtzapffel lathe is equipped with both the metalworking and the lighter ornamental-turning slide rests. They are interchangeable.
The ornamental slide rest has a much greater throw -- the distance the cutter can be moved from left to right by the lead screw without moving the rest—and this contributes to its greater flexibility. An elevating screw in the base of the slide rest allows for easy adjustment so that the cutter aligns with the exact height of center of the work, a very important matter in ornamental turnery.
A number of variations to the basic slide rest on the ornamental lathe have been designed and made by mechanically minded turners as well as the lathemakers themselves. Among these is the oval slide rest described by S. G. Askey in the February 1950 issue of the Bulletin of the Society of Ornamental Turners; only three oval slide rests are known to have been made. The spherical slide rest is another variation; the Reverend C. C. Ellison's private notebook states that he bought one in 1884 for £70. These slide rest variations are among the more exotic attachments to the ornamental lathe. The average turner will never need one.
INDEXING PLATE. The indexing plate is not really an attachment to the lathe but is an extension of the headstock pulley. The headstock contains a step pulley, the face of which contains several rows of evenly spaced holes that accept an index pin. An indexing plate makes it possible to fix the work in position so that it does not move while the whirling cutter produces the pattern. Moving the index pin to the next or desired hole will rotate and hold the work a fixed distance from the previous position. This may be repeated all the way around the work to produce an evenly spaced pattern.
Different lathes have different numbers of rows of holes in the indexing plate. My Holtzapffel lathe has four rows of 96, 112, 144, and 360 holes. A fifth row of 120 holes is sometimes desirable. Some lathes, such as the Evans, have so many rows of holes that it is easy to put the pin in the wrong hole, sometimes with devastating results to the cutting pattern. Using an indexing plate requires close attention and patience in placing the pin.
The shank of the pin for the indexing plate has a vernier screw in the stem or at the base that allows for infinite adjustments in the division of the pattern.
OVERHEAD DRIVE. The most obvious attachment to the ornamental lathe is the overhead drive, which powers cutting tools held in the slide rest and enables them to turn. This overhead drive is not found on modern metalworking or woodworking lathes but is peculiar to the ornamental lathe.
Historically the overhead drive has undergone a number of variations. Lathes made before the nineteenth century did not have an overhead drive, as it was a Holtzapffel development to replace former methods of activating the cutters. The motive power for the overhead originally came from a secondary belt running from the treadle and flywheel under the lathe. This belt turned the cylinder on the overhead, which had another belt that extended to the receptacle holding the cutter. The second belt could move across the overhead cylinder to follow the position of the cutter in the receptacle so that the cutter could move laterally. Tension on the belt that runs to the tool box has taken a number of different forms. A bow-and-spring arrangement was used on early overhead drives, but this proved to be inconvenient and was replaced with an arm with a counterbalance weight, which has greater flexibility.
My lathe, made in 1853, evidently originally had an overhead bow-and-spring arrangement on vertical posts rising from the frame of the lathe, since the indentations on the leg supports still show. At some point, some owner replaced it with a single post rising from the left end of the lathe frame. This post supports a cross member in a swinging position, counterbalanced with an iron ball on the outside end of the member. The inside end of the member holds permanently graphited wheels, which carry the belt from a motor mounted on the upright post to the cutting frame in the slide rest. This has proven to be a most convenient arrangement with easy positioning of the overhead belt to meet any desired position of the cutter. Ordinary dental belts can be used quite successfully in the overhead drive.
CHUCKS. The active ornamental turner never has quite enough chucks. Thirty-four different chucks came with my lathe, and at the time, there seemed to be enough of them to serve several workers. They all seem to get used sooner or later, however. Among the most frequently used chucks are the faceplate chuck and cup chuck, which are available in a range of sizes and are made of heavy brass. Probably the most used of all the chucks that came with my lathe is a four inch Cushman 3jaw self-centering chuck adapted to fit the mandrel nose. It has both inside and outside jaws. Other useful chucks include eccentric chucks, driver chucks in two sizes, metalholding as well as wood and ivory-holding chucks, spiral chucks, and elliptical chucks.
Some very complicated chucks, particularly the elliptical, geometric, epicyclodial, and rose engine chucks, have been designed and made for the lathe. These may be considered exotic attachments, made either to satisfy the creative instincts of a master toolmaker or to resolve a particular turning problem and probably never used again.
CUTTING FRAMES. Cutting frames hold the cutters in the receptacle or tool box on the slide rest. The tool box contains a groove, into which the 9/- inch-square shanks of the cutting frames fit. Some shanks are solid while others are drilled longitudinally to accept a revolving stem. This device cuts circles of predetermined radii on the work and can implement many interesting designs. The barleycorn pattern is made with this cutting frame.
Basic ornamental turnery requires only three cutting frames to do a wide range of work: the vertical, the horizontal, and the drill. Both horizontal and vertical cutting can be done with the universal, which can be positioned at all angles through 180 degrees -- 90 degrees to the right and left.
Other cutting frames are the side cutter and, for the more exotically inclined, the elliptical, the epicyclodial, and the rose cutting frames. These are not necessary for the average ornamental turner. All are described in the Holtzapffel volumes.
SPIRAL APPARATUS. The spiral apparatus consists primarily of three parts: a special chuck, a banjo arm, and a series of gear wheels, plus special fittings for its assembly.
The spiral chuck screws onto the inner end of the headstock shaft, or mandrel nose, and has a secondary nose that carries the work. It also carries the first of the train of gear wheels. It has a special indexing wheel with a spring-loaded arm with four teeth that engage the ninety-six teeth on the chuck's indexing wheel, thus taking the place of the ninety-six holes in the main index on the face of the pulley. This limits the indexing of spirally turned pieces to divisions of ninety-six.
The banjo arm is a heavy brass arm that fits on the face of the headstock surrounding the base of the spiral chuck. The arm extends out toward the turner and has a slot that accommodates the fittings that hold the other wheels
in the gear train. It is fastened solidly to the headstock but can be moved up and down to accommodate different sizes of gear wheels on the arm. In use it is locked in position.
The spiral set consists of sixteen brass wheels of increasing sizes. The smallest wheel has 15 teeth; the largest has 144. The train itself can consist of either three or four wheels, with a fifth idler wheel added when the direction of the spiral must be reversed. With the various gear wheel settings, it is possible to cut spirals or threads with as many as forty turns to one inch or as few as one turn or thread in approximately seven inches -- the slow spirals used to decorate vases, candlesticks, and the like.
CURVILINEAR APPARATUS. This apparatus permits the decoration of curved surfaces, either straight or spiraled. It consists of posts mounted on either end of the slide rest that support a bridge that spans the entire length of the rest. Mounted on this bridge, a template governs the route to be taken by the cutter to decorate the curved surface.
To do this the tool box is freed from the collar that fixes it to its control screw. This permits it to move freely in and out, guided by a handle connecting the tool box with the frame of the slide rest. Mounted in the top of the tool box is a rubber, which has a shaped end that rubs against the curved edge of the template mounted on the bridge. Thus, the cutter follows the exact curvature of the template.
STEADYREST. On many occasions it is necessary to support the outer or tailstock end of the work when the tailstock cannot be used to do so. This happens particularly when end-boring or hollowing is being done. Holtzapffel made a boring collar which contained a series of holes spaced around the circumference to permit the entrance of a boring piece. However the largest hole in this piece is 13/4 inches in diameter, and in many cases a hole is needed to accept a greater bore in the piece being worked. The Holtzapffel boring collar does not provide this. Furthermore, the adjustment of that boring collar to the exact height of center is sometimes quite difficult.
The answer to this problem is a steadyrest. It is an octagonal metal frame -- placed over the work piece after the surface is trued -- with four pins spaced equidistantly around the circumference of the frame. The pins slide through holes in the frame until they rub the surface of the work. which is centered within and protrudes slightly from the frame. The pins are then locked in position. The inside diameter of the frame is slightly greater than five inches, large enough to accommodate most turnings. The steadyrest is very easy to mount. First, the workpiece, supported by the tailstock, is plain-turned to create a true surface that will accept the ends of the pins. With the work turning slowly and the tailstock in place, the pins are dropped into position on the surface of the workpiece. The pins are locked and the tailstock removed; the piece is now supported accurately on a centerline.
One of the most troublesome problems facing the ornamental turner is compiling a reasonably complete set of cutters. To illustrate: one turner in recent years bought a lathe only to discover that exactly one cutter came with it. On the other hand, a well-equipped lathe will have a hundred or more cutters.
TYPES OF CUTTERS. The cutters are tiny chisel-shaped tools that actually cut the patterns. They fit in the tool box receptacle in the slide rest and are not hand-held as are chisels in plain turnery. They come in different sizes, widths, lengths, and contours. Among the infinite variety of cutters are square-end, convex, concave, single-angle, double-angle, quarter- hollow, half-round (in matched pairs), and double-concave cutters, drills in most of these shapes plus drills in a stairstep pattern, thread cutters (in matched pairs), side cutters in various contours, plus many others. Each of the shapes comes in as many as twelve or fifteen widths. You can see how quickly a "complete" set of cutters can add up to many hundreds. In addition I have a small mahogany box fitted with fifty-four specially ground cutters in molding shapes. Who cut them? I don't know, but the box is obviously from the nineteenth century.
Holtzapffel made special mahogany boxes with drawers and hinged covers to hold the cutters. The boxes themselves are collector's items. Along with the cutters came special handles into which the cutter can be inserted and fastened with a brass thumbscrew. These handles allowed the turner to transform ornamental-turning tools into plain-cutting tools. Holtzapffel even included a special pair of tweezers for plucking the cutters from their nests.
SHARPENING THE CUTTERS. When I obtained my lathe, the friend in England who found it for me suggested, "Now that you have your lathe, I recommend two things. First, retire, and second, teach your wife to sharpen the cutters." Only the first has come about; the second is still a somewhat onerous task.
The standard sharpening device for ornamental cutters is called a goniostat. It is essentially a three-legged device of which the cutter forms the third leg. The two fixed legs move on a fixed surface while the cutter moves on a sharpening stone or a metal plate charged with lapping compound. The tool leg can be adjusted through angles of 54 degrees right and left for double-angled cutters and can be adjusted through 70 degrees in the other direction to accommodate the rake of the tool. The latter is normally fixed to a predetermined rake angle and not moved.
Another sharpening device, designed by the Reverend G. A. Grace, is similar in principle but takes a round-ended tool and rocks it back and forth on the stone, with excellent results.
Because delicate turned cuts cannot be finished with sandpaper, the cuts normally create the finished surface. This means the cutters must have razor- sharp edges. This is normally accomplished by the use of hard Arkansas stones.
Concave tools are sharpened with an appropriately sized cone. The cones come in sets of progressive sizes to accommodate all the diameters of the concave shapes. A device that fits on the slide rest of the lathe accepts and revolves these cones, which are charged with lapping compound for sharpening. There are two sets of cones: brass for first sharpening and iron for the final grind. Lapping compounds range from 120 to 1000 grits.
Sometimes it becomes necessary to pause in the middle of a cutting operation to resharpen the cutter. It is important to very carefully reposition the cutter in the cutting frame after sharpening it. Otherwise the design will be moved slightly out of position; this mistake may be surprisingly visible in the finished piece.
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