Pantograph


A pantograph is a mechanical linkage connected
in a manner based on parallelograms so that the movement of one pen, in tracing an image,
produces identical movements in a second pen. If a line drawing is traced by the first point,
an identical, enlarged, or miniaturized copy will be drawn by a pen fixed to the other. Using the same principle, different kinds
of pantographs are used for other forms of duplication in areas such as sculpture, minting,
engraving and milling. Because of the shape of the original device,
a pantograph also refers to a kind of structure that can compress or extend like an accordion,
forming a characteristic rhomboidal pattern. This can be found in extension arms for wall-mounted
mirrors, temporary fences, scissor lifts, and other scissor mechanisms such as the pantograph
used in electric locomotives and trams. History
The first pantograph was constructed in 1603 by Christoph Scheiner, who used the device
to copy and scale diagrams, but he wrote about the invention over 27 years later, in “Pantographice”. One arm of the pantograph contained a small
pointer, while the other held a drawing implement, and by moving the pointer over a diagram,
a copy of the diagram was drawn on another piece of paper. By changing the positions of the arms in the
linkage between the pointer arm and drawing arm, the scale of the image produced can be
changed. A more complicated version called the eidograph
was developed by William Wallace in 1831. Uses
Drafting The original use of the pantograph was for
copying and scaling line drawings. Modern versions are sold as toys. Sculpture and minting
In sculpture, a three-dimensional version of the pantograph was used, usually a large
boom connected to a fixed point at one end, bearing two rotating pointing needles at arbitrary
points along this boom. By adjusting the needles different enlargement
or reduction ratios can be achieved. This device, now largely overtaken by computer
guided router systems that scan a model and can produce it in a variety of materials and
in any desired size, was first invented by inventor and steam pioneer James Watt and
perfected by Benjamin Cheverton in 1836. Cheverton’s machine was fitted with a rotating
cutting bit to carve reduced versions of well-known sculptures. Of course a three-dimensional pantograph can
also be used to enlarge sculpture by interchanging the position of the model and the copy. Another version is still very much in use
to reduce the size of large relief designs for coins down to the required size of the
coin. Acoustic cylinder duplication
One advantage of phonograph and gramophone discs over cylinders in the 1890s—before
electronic amplification was available—was that large numbers of discs could be stamped
quickly and cheaply. In 1890, the only ways of manufacturing copies
of a master cylinder were to mold the cylinders, to record cylinders by the “round”, over and
over again, or to acoustically copy the sound by placing the horns of two phonographs together
or to hook the two together with a rubber tube. Edison, Bettini, Leon Douglass and others
solved this problem by mechanically linking a cutting stylus and a playback stylus together
and copying the “hill-and-dale” grooves of the cylinder mechanically. When molding improved somewhat, molded cylinders
were used as pantograph masters. This was employed by Edison and Columbia in
1898, and was used until about January 1902. Some companies like the United States Phonograph
Co. of Newark, New Jersey, supplied cylinder masters for smaller companies so that they
could duplicate them, sometimes pantographically. Pantographs could turn out about 30 records
per day and produce up to about 150 records per master. In theory, pantograph masters could be used
for 200 or 300 duplicates if the master and the duplicate were running in reverse and
the record would be duplicated in reverse. This, in theory, could extend the usability
of a pantograph master by using the unworn/lesser worn part of the recording for duplication. Pathé employed this system with mastering
their vertically-cut records until 1923; a 5-inch-diameter, 4-or-6-inch-long master cylinder,
rotating at a high speed, would be recorded on. This was done as the resulting cylinder was
considerably loud and of very high fidelity. Then, the cylinder would be placed on the
mandrel of a duplicating pantograph that would be played with a stylus on the end of a lever,
which would transfer the sound to a wax disc master, which would be electroplated and be
used to stamp copies out. This system resulted in some fidelity reduction
and rumble, but relatively high quality sound. Edison Diamond Disc Records were made by recording
directly onto the wax master disc. Milling machines Before the advent of control technologies
such as numerical control and programmable logic control, duplicate parts being milled
on a milling machine could not have their contours mapped out by moving the milling
cutter in a “connect-the-dots” fashion. The only ways to control the movement of the
cutting tool were to dial the positions by hand using dexterous skill or to trace a cam,
template, or model in some way, and have the cutter mimic the movement of the tracing stylus. If the milling head was mounted on a pantograph,
a duplicate part could be cut simply by tracing a template. This was essentially the same concept as reproducing
documents with a pen-equipped pantograph, but applied to the machining of hard materials
such as metal, wood, or plastic. Pantograph routing, which is conceptually
identical to pantograph milling, also exists. The development and dissemination throughout
industry of NC, CNC, PLC, and other control technologies provided a new way to control
the movement of the milling cutter: via feeding information from a program to actuators that
would move the cutter as the information directed. Today most commercial machining is done via
such programmable, computerized methods. Home machinists are likely to work via manual
control, but computerized control has reached the home-shop level as well. Thus pantograph milling machines are largely
a thing of the past. They are still in commercial use, but at a
greatly reduced and ever-dwindling level. They are no longer built new by machine tool
builders, but a small market for used machines still exists. As for the magnification-and-reduction feature
of a pantograph, it is achieved in CNC via mathematic calculations that the computer
applies to the program information practically instantaneously. Scaling functions are built into languages
such as G-code. Other uses
Perhaps the pantograph that is most familiar to the general public is the extension arm
of an adjustable wall-mounted mirror. In another application similar to drafting,
the pantograph is incorporated into a pantograph engraving machine with a revolving cutter
instead of a pen, and a tray at the pointer end to fix precut lettered plates, which the
pointer follows and thus the cutter, via the pantograph, reproduces the ‘copy’ at a ratio
to which the pantograph arms have been set. The typical range of ratio is Maximum 1:1
Minimum 50:1 In this way machinists can neatly and accurately engrave numbers and letters
onto a part. The device which maintains electrical contact
with the contact wire and transfers power from the wire to the traction unit, used in
electric locomotives and trams, is also called a “pantograph”. Some types of trains on the New York City
Subway use end pantograph gates to prevent passengers on station platforms from falling
into or riding in the gaps between the cars. Old-style ‘baby gates’ used a 2-dimensional
pantograph mechanism as a means of keeping toddlers away from stairways. The openings in these gates are too large
to meet modern baby gate safety standards. Herman Hollerith’s “Keyboard punch” used for
the 1890 U.S. Census was a pantograph design and sometimes referred to as “The Pantograph
Punch”. An early 19th-century device employing this
mechanism is the polygraph, which produces a duplicate of a letter as the original is
written. A polygraph is a machine that was and still
is used by most government branches for detecting lies of the people they are trying to get
information from. The pantograph mechanism helped the idea to
scribble figures onto a roll of paper to tell when the blood pressure or pulse changes after
the individual hooked up gives a response to the question. Longarm quilting machine operators may trace
a pantograph, paper pattern, with a laser pointer to stitch a custom pattern onto the
quilt. Digitized pantographs are followed by computerized
machines. Linn Boyd Benton invented a pantographic engraving
machine for type design, which was capable not only of scaling a single font design pattern
to a variety of sizes, but could also condense, extend, and slant the design. Pantographs are also used as guide frames
in heavy-duty applications including scissor lifts, material handling equipment, stage
lifts and specialty hinges. Richard Feynman used the analogy of a pantograph
as a way of scaling down tools to the nanometer scale in his talk There’s Plenty of Room at
the Bottom. Numerous trade-show displays use 3-dimensional
pantograph mechanisms to support backdrops for exhibit booths. The framework expands in 2 directions from
a bundle of connected rods into a self-supporting structure on which a fabric backdrop is hung. See also
Autopen James Watt’s parallel motion
Polygraph Scissor mechanism
Spirograph References External links
Pantograph Java applet Pantograph at mathworld.wolfram.com
How to build a pantograph 3 D Pantograph Process
Pantograph Cradle used in Building Facade Access System

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