Definizione

• Pantograph, Die-engraving Pantograph.  A machine for reducing three-dimensional bas-relief designs while simultaneously cutting a steel die. The mechanical engraving machine, which was early called a portrait lathe and later called a reducing machine among other names, eliminates the requirement of manual labor to meticulously cut dies by hand engraving. It had the further advantages that many dies could be cut from one pattern, more than one size die could be reduced from the same pattern, the pattern could be seen complete before being placed into production of diecutting, and the ease of which design errors could be corrected.
  The use of the pantograph in early mints – like the use of the collar, certain other
  blanking and striking techniques – was part of the mystic of coin making. As such, it was part of the technology closely guarded by mint personnel. To safeguard against coin counterfeiting early on the knowledge of the pantograph was not revealed to a general public (in England or America, but was published as coining technology in France and Germany).
  At first the die-engraving pantograph was employed only to cut the main device of a coin or medal design – primarily the portrait and called a reduction punch – where lettering, dates and additional ornamentation was added by punches and hand engraving afterwards. With improved development of its mechanics, later die-engraving pantographs (those of the 20th century) could reproduce the entire design, cutting a finished die, lettering and all, from a complete pattern.
  Hard-surface pattern required.  The machine requires an oversized model as the source of the three-dimensional design – a pattern or master. This must be in hard material (or at least have a hard surface) because a tracer (tracing stylus) must ride over this surface. Early masters were cast or carved in metal (iron, bronze, brass) even cut in stone.
  Early patterns of cast iron were made in both England and America for both coin and medal dies. As such it bore a more rounded detail lacking sharp, crisp edges. Metal casting lacks such edges because of meniscus (where metal does not flow into crevices of the model). Also important was the investment use for the casting. If this was wet sand the surface was not always smooth. An iron cast had to be worked afterwards to smooth all surfaces and sharpen all edges of detail.  
  In the 1850s electrotypy had developed whereby a hard medal pattern could be electrolytically cast in copper or nickel from a model made of wax, clay, plasteline, plaster, wood or other composition. These electrogalvanic casts – called galvanos
  – proved excellent for the patterns used in mechanical engravers and replaced earlier iron patterns.
  Not only were galvanos easy to make but even more reason for their fidelity to the original model in hard metal surface. Also steel tracing points as a stylus, could easily track the copper surface (even without a lubricant). The cutting point was shaped so that it had two cutting surfaces that made two cuts with each revolution (see illustration).
  Die cutting simultaneous with reduction. A steel die block of proper size and trueness is planed to have a smooth face; it is heat treated, annealed, until it is dead soft. This is mounted in the mechanical engraver to be cut into the die. Early reducing machines had a fixed cutter, later ones employed rotating cutters. The stylus (tracing the relief on the pattern) and the cutting point (drilling into the steel) are both mounted on a long bar, pivoted at one end, which transfers the position, degree and depth to be cut into the die block.
  The stylus (tracing stylus or tracing point) starts at the center of the
  pattern, and the cutting point starts at the center of the steel block, both progressing simultaneously outward towards the edge of the design. The tracer plays across the
  pattern’s bas-relief surface from center outwards on most mechanical engravers (only one pantograph [Keller] starts at the edge and transverses inwards – like a phonograph player).
              Dies cut on early pantographs, or later by unskilled operators, often exhibited concentric circles, the trail of the cutting tool on the surface of the die. These lines require removal in the die by smoothing the surface, by BURNISHING or CHASING, a REWORKING of the die. If not they will obviously show on all struck pieces. While such concentric circles are not a diagnostic of cast iron models they were prevalent during the period such iron models were used.
  Modern pantograph’s other options.  The mechanics of the die-engraving pantograph are such that it can cut either incise relief or raised relief (as hubs or finished objects). The modern machines can even regulate the height of the relief, or, amazingly, reverse polarity (a right-facing portrait can be changed to a left-facing portrait). It can also change or add a die camber (shape of the table or background). Further, it can even enlarge as well as reduce a design!
  In addition to these mechanical techniques is a seldom-used technique, these machines can, in effect, become a reproducing machine. They can cut a design into a composition that cannot be stamped, as ivory, bone or plastic.
  Modern history. The most modern medallic engraver was developed by a
  Frenchman, Victor Janvier (1851-1911), and his Janvier reducing machine became the premier die-engraving pantographs of the 20th century. The earliest instruments were merely copying lathes or cameo cutters, but the remarkable contrivance has been called a wide variety of names over the years: tour a reduire, tour a portrait, medallion engraver or lathe, portrait lathe, transfer lathe, reducing machine or lathe, diesinking machine, mechanical engraver, pantographic reducer, medal reducing lathe, medal and cameo reducing and engraving lathe, and, finally, by their maker's name (as Hill, Contamin, or the famed Janvier).
  The products which can be created from dies made by this method are not limited to coins, medals and cameos in all, but also anything coined. Any small object struck in a press from dies, as buttons, emblems, jewelry items, small parts and such, even tableware utensils could be coined. (It was not surprising that the tableware industry early embraced the Janvier and acquired more of these machines than any other industry.)
  But what was so astonishing was the mint officials of the world who had to create high quality coin dies beating a path to the door of Janvier's small Paris factory. In the early 20th century if modern mints wanted quality diecutting and the highest fidelity coin reductions they needed a Janvier engraving machine.
  History of the Die-engraving Pantograph
  Existing records of the earliest known machines which reproduce three-dimensional images were either copying machines or virtual cameo-cutting lathes. These existed in England, Europe and Russia. They could reproduce a design in metal, but nothing as hard as steel.
  The first true die-engraving pantographs were developed independently in France and the Low Lands. They not only had a bar affixed to a fulcrum, which provided the required reduction, but also the ability to cut into steel. These included the Hulot (no other name recorded) whose machine appeared in Belgium in 1766. This early reducing lathe was to have an influence on others who built improved pantographs in a number of countries. One of Hulot's machines still exists in a Brussells museum today as tacit testimony to this early creation.
  In France, Saxton Merchlein, a machinery inventor, developed his reducing machine in 1767; while contemporary with the Hulot, each was developed independent of the other. Merchlein's machine was perhaps the first to be used for engraving coin dies at a mint, the Paris Mint.
  Privately in France, Jean Baptiste Barthelemy Dupeyrat (1759-1834), a young mechanic, had developed a reducing lathe that attracted the attention of Matthew Boulton. Boulton obtained one of Dupeyrat's lathes in 1790 for his Soho Mint in Birmingham.
  Obviously national mints in both France and England became interested in these machines, leading to a second generation of improvements. However, it was the private industry in both these countries that were to do the most to advance the mechanical engraver. Engineering developments in private industry were quickly assimilated in the equipment of national mints; but the technology did not flow in the opposite direction.
  New ideas developed in national mints became closely guarded secrets. Advancement in the field – particularly for medals – had to come from private mechanical engineers working independently outside any national mint.
  Second generation machines were built by Belgium medallist Joseph Pierre Braemt (1796-1864) in 1824 (undoubtedly based on the Hulot machine of his countryman). Braemt's machine still exists in the Brussells Mint Museum. Also the Hulot machine inspired one developed by Benjamin Cheverton, a British machinist in 1826.
  In addition to the private Soho Mint, Dupeyrat's machines were sold to the British Royal Mint, in 1819, to the Karlsrue Mint in Germany, and other European mints about the same time. When James Watt, Boulton's partner in the Soho Mint, retired in 1804 he worked on improving the Dupeyrat lathe, continuing his endeavors until his death in 1819.
  In France in 1820 an ingenuous machinist Ambrose Wohlgemuth built a "medal and cameo reducing and engraving lathe." He used modern principles of reduction but still employed pedal power, as had all previous machines. His lathe still exists and is in the Conservatoire des Arts et Metier, Paris.
  A decade later in Beasancon France, a surgeon who took up sculpture, Jean Baptiste Maire (1787-1859) developed his own reducing machine after creating his first medals in 1834. Perhaps it was used by the Paris Mint since it is in the Conservatoire des Arts et Meitiers alongside Wohlgemuth's machine.
  All first and second generation reducers had a fixed cutter; the work rotated while the cutting point was fixed to the bar. This was a true lathe. Third generation reducers employed the rotating cutting point; in effect transforming the medallic pantograph into a mechanically controlled milling machine.
   
  France's Contamin (again, no other name known, and his dates unknown) working in Paris created an improved machine with a rotating cutter, called a Tour de Médailles. This success led to widespread use of his machine. Probably developed prior to 1834, when Franklin Peale observed it that year. In 1836 Peale obtained the Contamin engraver for the United States Mint at Philadelphia. While not associated with the Paris Mint, Contamin was able to offer his machine to any buyer in any country, thus its influence was widespread.
  A generation later, England's Charles John Hill first developed his machine in 1851 with further improvement in 1856. While he may have seen James Watt's improved diecutter at the Soho Mint, he most certainly had knowledge of the Contamin. Hill's die-engraving pantograph was patented in 1866 and at first he only wanted to do die-cutting reductions, preferring not to let the machine out of his control. It was only when William Wyon purchased Hill's machine, obtaining all rights to it that it could be sold to others. It was built and marketed by George Wailes & Company, a machinery manufacturing firm of Vauxhall.
  Victor Janvier's period of developing his remarkable machine occurred in the 1890s. An accomplished medallist, he formed a partnership in 1892 with Paul Marie Duval to do custom enlarging and reducing, to cut dies, and even to manufacture medals. Undoubtedly his dissatisfaction with existing machines, notably Hill's and Contamin's, led to his experiments to improve the mechanics and to construct his own reducing lathe.
  The problem with existing reducers was the speed of the revolving model and the
  die block. Janvier's solution was inspired. He provided a slow revolving speed of the model at the beginning when the tracer and cutting point were both in the center. At the end he needed just the opposite speed: greater speed of the model and slower rotation of the die.
  He accomplished this by twin cone axis pointing in opposite directions with a belt connecting them. One axle drove the rotation of the model (this was slow at the beginning, increasing in speed as it reached the edge of the pattern). The other drove the rotating chuck holding the die block (it was rapid in the beginning and slower at the end). Neither of these affected the speed of the rotating cutter point (which was driven by a belt in some machines, by a separate motor in others). Janvier’s concept was simple – a mechanical mechanism to effect the change in speeds at different stages of the die engraving progress – simple but highly effective. Janvier build his machines with the quality of a Swiss watch.
  Janvier's improvements created a smooth running mechanism with watch-like accuracy. He was granted a French patent in1899 and he created a second business, Ateliers Victor Janvier, to commercialize on his invention by building and selling his die-engraving pantographs to mints and manufacturers throughout the world.
  Janvier's machines sold but not without some persuasion. For example, the United States Mint at Philadelphia were still using their 50-year old Hill lathe – for portraits and devices as reduction punches – with decreasing satisfaction of the engraving department.
  In New York City at the turn of the century a couple of German brothers who were in the ladies handbag business sent a new employee, French-born Henri Weil, to France to see why the metal decoration of French handbags were better than any other. Weil cabled the Deitsch Brothers, the decoration was made on the best reducing machine manufactured in Paris, a Janvier.
  The Deitschs wired in return: "Buy machine. Learn its operation. Bring to New York." Weil did just that, bringing the machine back with him in 1906. This was the beginning of the Janvier in America and what was to become the Medallic Art Company.
  The Deitsch brothers liked the machine so well they became the exclusive agents for Janvier in America. But it took the intervention of a sculptor, Augusts Saint-Gaudens, and a U.S. president – Theodore Roosevelt – to insist the U.S. Mint buy a Janvier to replace their Hill reducer. It did so in 1906. The Philadelphia Mint had been considering obtaining a new reducing machine for several years. The delay in buying one from Keller Mechanical Equipment Co., or some other, was the indecision by Engraver Charles Barber. The President’s pressure forced their decision to obtain a Janvieer from the Deitsch Bros. in New York City.. Henri Weil, then an employee of the Deitschs, went to Philadelphia to instruct engraving department employees how to operate it.
  Henri Weil and brother Felix were to later acquire the distribution rights of all Janvier's machines in the U.S. as a collateral business to their medal manufacturing (which continued until the 1960s) as part of Medallic Art Company, which they acquired from the Deitsch Brothers in 1909.
  By 1921 Janvier's reputation was widespread and his reducing machines were in 22 countries around the world. The number built and shipped by country are listed in the adjacent box.
                               Number to   Number to       
                                National    Private        
                                 Mints       Firms *      
                                                           
           France . . . . . . .  -            33          
           United States. . .  -            23          
           Austria. . . . . . .    2           14           
           Germany. . . . . . . -            13          
           England. . . . . . .  3            11          
           Spain. . . . . . . .    2              6          
           Italy. . . . . . . .      2              5          
           Belgium. . . . . . .  1              3          
           Netherlands. . . . . 1             3          
           Japan. . . . . . . .     1             3          
           Denmark. . . . . . . 2             1          
           Switzerland. . . . . -              2          
           Czechoslovakia . .2             -          
           Mexico . . . . . . .    -             1          
           Brazil . . . . . . .      1             -          
           Hungary. . . . . . .   1             -           
           India. . . . . . . .       1             -          
           Poland . . . . . . .     1             -          
           Russia . . . . . . .     1             -          
           Siam . . . . . . . .     1             -          
           Sweden . . . . . . .   1             -          
           Turkey . . . . . . .    1             -          
                       Total. .    24         116          
                                                           
   *  Some private firms were agents, who, in turn resold  
      reducing machines to national mints, as in the case  
      of United States. Also, once a mint or firm had one  
      reducer, they often ordered more. Not all the machines
      sold to private firms were used for making coins and 
      medals (as manufacturers of buttons and silverware   
      obtained these machines perhaps in greater numbers   
      than mints, national and private).                   
          Ratios and Restrictions
  Because the center axle of the model cannot be the same as the axle of the cutting tool, a reducing machine cannot cut a one-to-one replica. There must be space between the two axles (enough in fact for the chariots to hold the tooling for each). If the pattern isn't too large a ratio of 1.5-to-one can be cut on die-cutting pantographs. The more preferred ratio, however, is three- or four- or five-to-one.
  Nevertheless, the limit of reduction is about ten-to-one on the more modern pantographs. Some reducing machines have been built, however, to accommodate a model-to-die ratio of as much as 20-to-1. Since most coins are 1 1/2-inch or smaller, their models are most often about 6 to 9 inches in diameter. Medals are somewhat larger; a medal 2 1/2 to 3-inch in diameter would best reduce from a 9 to 18-inch diameter model.
  If the model is inordinately too large – or the desired die too small (as a charm size) – an intermediate reduction is made, cast into a new pattern and reduced again. Since this intermediate step most often is cut in beeswax or paraffin (for quick cutting in a material easily cut into a new pattern), this is often called a wax reduction.
            Action of Pantograph Described
  The diemaker must know the process for which a pair of dies are intended, he receives a work order which states the type of press and a diameter to cut the dies. He is also furnished a metal or epoxy pattern (dieshell) from which to cut the die. He will mount the pattern dieshell in the die-cutting machine (Janvier reducing machine or other diecutting pantograph). He will also mount a die block of proper diameter and thickness in the pantograph (die blocks are cut from roll stock or bar stock and face trimmed on both ends – these two surfaces must be parallel!). A diestock wider than the intended diameter of the medal is chosen (see chart).
  A tracing point (stylus) is set to play over the face of the pattern, dieshell
  hubshell, its bas-relief contour allows the tracing point to rise and fall with the rise and fall of relief. This action is transferred to the cutting point by a long bar to which they are both attached. The distance from the centers of the two – dieshell and diestock – determines the percentage of reduction to effect the desired diameter of the image size, and thusly the diameter of the medal. (The ratio and this distance is critical to obtain the correct diameter image to be cut on the die.)
  The mechanism of the pantograph is such that the stylus travels outward a tiny fraction of an inch while the dieshell is slowly rotating. Likewise the diestock is rotating at the same speed and the cutting point is actually cutting into the diestock the depth allowed by the bar guided by the pattern. Once it reaches its outermost position (to the edge of the relief of the pattern) it will automatically shut off. (Thus once a pantograph is set in motion and is performing satisfactorily it can run unattended by its operator, even into the night, or into the weekend – all machines are set to operate by Friday pm, on Monday morning all work is accomplished!). If cutting was interrupted such as by a power failure or broken tracing point, then entire work often had to be restarted from the beginning.
  Without removing either the pattern or dieshell a second and third cut are performed in much the same manner. With each new setting a finer tracing stylus is used and a finer cutting point is used; thus all the relief in the pattern is reproduced in the die. The last cut – the final cut – is the finest of all and all the relief in its infinite detail should be reproduced in the die.
  The die is then removed from the pantograph, inspected and proven with a lead impression (see proving). If all is satisfactory it is marked for matching obverse and reverse (see die alignment) then hardened by heat treating.
          Other Reducing Machine Functions
  In addition to reducing and cutting dies from oversize patterns, modern die-engraving pantographs can also do other functions. These include the following:
  Height of relief.  By adjusting the pivots the height of the relief can be raised or
  lowered in direct proportion. This produces a slight variance from the pattern, but is often required to accommodate a different press or process. Models intended for medium or low relief medals can sometimes be reduced and relief lower enough to be coined (instead of requiring a sculptor to remodel in coin relief).
  Contraposition.  By adjusting the gears on a reducing machine, the die can be made in contraposition to the model – again in direct proportion. A portrait facing right, for example, can be changed to face left. This is satisfactory for a simple device or portrait, but unsatisfactory for lettering, as it reverses it (called retrograde lettering). The Philadelphia Mint did this in one instant in 1920 for the Manila Mint Opening Medal. The kneeling female figure device employed on Assay Medals from 1882 to 1892 facing right was employed for the Manila Mint medal where the device faces left.  See contraposition for an example in medallic art.
  Die camber.  Because of the requirement of circulating coins to have a rim higher than all relief (to reduce wear) sculptors often prepare coin models on basins (a background plate that slopes very slightly downward from the rim). If this is not done and the model is prepared flat, say, the die-engraving pantograph can be adjusted in such a way that the die can be cut with a camber. This will cut a die with the required convex curvature of the table or background. By lowering the design – slightly near the rim and more so in the center – all relief will be below the rim.
  Pantograph Anomalies
   
              Most errors on a pantograph are caused by an operator, incorrect settings or improper seating of die stock or dieshell for the most part. The machine only does what it is setup to perform. An inexperienced or careless operator can cause the most obvious anomaly, evidenced as concentric lines on a die that was placed in production without first being polished. These are sometimes called pantograph lines.
              A broken tracer is an error on a pantograph. See box at the entry on ERROR.
  References:                                                                                                                          
  C43 {1966} Gilbert, #202, 207, 208, pp 84-87, plate 17.
  C66 {1988} Cooper, pp 164-170, 237.

  excerpted with permission from

  An Encyclopedia of Coin and Medal Technology

  For Artists, Makers, Collectors and Curators

  COMPILED AND WRITTEN BY D. WAYNE JOHNSON

  Roger W. Burdette, Editor

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