Definition
"A jig is a device that holds the work and guides
the tool...; while a
"fixture simply holds the part as it is being
worked" For the
woodworker, a jig is an
on-the-spot device created to make the cutting or shaping of a part the
wood in a project either more safe, more efficient, more accurate, more
rapid, or any of a multitude of other reasons. (More
than any other tool
or technique in the woodshop, jigs and fixtures demonstrate the
"bottom-up" aspect
of woodworking; that is, it is a truth that the majority of woodworking
devices created result from woodworkers solving a problem on the the
floors of their shops: It could have been
seeing that a single-edged chisel would be made more efficient by
having a series of edges, and thus the first multi-toothed hand saw was
conceived. Or, that by filing a profiled-edge on a plane's iron, and
creating a decorative molding. And a multitude of other ideas about
doing a woodworkking operation more effieciently, more safely,
etc. For early historical development,
these topics
covered in W L Goodman's The History of Woodworking
Tools London: Bell, 1964. See also Sources
section at the end of this page. I have discussed the
evolution of the woodworker's cutting
edge in greater detail in
Appendix 8.)
[Suggested
Definitions]
After
circulating this larger draft -- on jigs/fixtures
-- to a circle of friends, I received the response directly below from
Charlie Belden, a woodworker friend (and webmaster) who lives in
Silicon Valley, California. He agrees that Jig and Fixture have a
conceptual linkage, but in addition, he claims that guide, template, pattern
and form also share a piece of the same concept, if I may put it in
such terms.
I agree with Charlie, but -- at the moment -- hesitate at any
attempt to combine into a single entry a discussion of all five of
these terms. Instead, as a sort of mental reminder, I choose to set the
five terms out, and think about how they should be treated. Thoughts from readers about these matters are welcome.
Jig:
a device which positions two or more objects to a location in
space such that degrees of freedom of movement of the objects relative
positions are limited to movement along, or rotation about, a single
axis.
Fixture: a device which
secures a single object to a location in space
relative to a specific reference plane and/or point by limiting at
least four of its possible six degrees of movement in space ( the
possible six degrees of freedom of movement being movement along the x,
y and z axis and rotation about said axis)
Guide:
as in "a drilling/boring guide", which -- in fact -- may be
more of a very specialized Template.
Template:
an object, real or virtual, whose outline, or a specific
portion of its outline, is followed directly or indirectly by a
material removal tool
Pattern:
an object, real or virtual, with a specific set of dimensions in 2-D or
3-D, used as a reference for reproducing one or more of that
object’s
dimensions by whatever means, either exactly or at any scale.
The
means of actually creating the reproduction may or may not have direct
phyisical contact with the PATTERN during the material removal
operation, unlike a template which always requires contact with the
wood removal tool.
Form: a device
to which one or more object or set of objects is/are made to conform in
order to create a specific surface shape.
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Use of These
Terms in the Literature
JIGS
AND FIXTURES
Broadly
speaking, a jig or fixture is any device that guides drills
or
other tools so as to produce work that is interchangeable
within the
tolerances set by manufacturing requirements.
The same terms are also used for devices or frames that hold
pieces in
their proper position while being welded. or otherwise joined
together.
We
are, however, most interested in devices for hold-
ing work during various machining operations, and jigs and fixtures of
this class will receive the greatest attention.
A distinguishing definition for jigs and fixtures that seems to be
generally accepted is about as follows: A jig is a work-holding,
device which is not fastened to the machine on which it is used.
A fixture is
also a work-holding device but one that is bolted or
otherwise fastened to the machine. The jig, for example may
be moved around on the table of a
drill press to bring each bushing under the drill spindle. A fixture,
on the other hand, is fastened to the table or base of a machine, and
either the tool is moved to the point of operation, as in the case of a
radial drill; or the table is moved under the cutting tools, as in a
milling machine. This definition, however, has not been offically
standardized
Source: Fred H Colvin, Jigs
and Fixtures: A Reference Book, Showing Many Types of Jigs and Fixtures
in Actual Use, and Suggestions for Various Cases.
1913, page 1 (I checked the text of subsequent editions, 1922 and 1938,
and found the definitions unchanged.)
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The
box below contains a fragment
of R J Decristoforo's Introduction
to one of at least two books he dedicated to "jigs'. The "bottom-up"
nature of jigs -- they start out in homeshops but after patenting, end
up on the floor of woodworking stores or in catalogs of woodworking
tool distributors -- is illustrated in the highlighted text
from
Decristoforo's book:
A
jig is an accessory that's
custom made. It might be a quick assembly to solve a one-time chore
but, more often, it becomes as permanently useful as the tool on which
it was designed to be used. Many times, the project enables you to
extend the applications of a tool beyond its basic functions. Simple or
complex, jigs are a bridge to more competent woodworking....
Jigs work in various ways ....
Some jigs are designed out of downright necessity....
Jigs are getting a lot of attention these days, to the point
of being commercialized ....
In the final analysis, a jig must be a practical accessory, fun and
reasonably easy to produce. But it must be carefully made....
Source: R J Decristoforo The
Ultimate Jig Book. Cincinnatti: Popular Woodworking
Books, 1999, page [6-7]
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(On
the left, for example, is a "jig" I
use to accurately cut sides for picture frames. This jpg shows the
frame being made out of weathered barn wood. The device holds the
workpiece at a 30° cant.
Read more here.
Regular
readers will
soon detect that the "bottom-up" issue in woodworking is a matter about
which I have considered at length. Why? Because I think that "jig
making" is an essential component of woodworking, a principle that can
be proven by disassembling a woodworker's bench -- itself a "jig" --
into its component parts: Vise, Bench Dog,
Bench Stop, Bench Hook,
or Bench Screw, (or what R A Salaman calls "Bench
Chops" -- for all of these "jigs", see R A Salaman, Dictionary
of Woodworking Tools, 2d ed revised, New town, CT:
Taunton Press, 1989). Put
simply, for me, the Workbench is itself a
woodworker's "tool", and all of the apparatus that embellish
workbenches today started out as jigs and/or fixtures. The Vise on
a workbench, for example, because -- for many generations -- it has
been an attached integral component of
workbenches.
The
same can be said about origin as jigs of the Sleds,
the Miter Squares, the Table Slots,
the Zero Clearance Inserts and multitude of other
jig-like devices that comprise the standard gear for today's Table
Saw. The Biesemeyer fence is an example of a "jig", and
definitely falls under the rubric of "bottom up" development.
In 1943 Donaldson and LaCain used this:
A
jig is a device for insuring that a hole to be drilled, tapped, or
reamed in a machine part will be machined in the proper
place The term
"jig" should be used only for devices to be used while drilling,
reaming,, or tapping holes, as de.. fined above. If the operation
includes machining operations like milling, planing, shapiig and so on,
the term fixture should be used.
Source: Cyril
Donaldson and George H. LeCane, Tool Design,
(New York: Harper
and Brothers, 1943, page 253
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Girardot
and Karosh, co-chairmen in writing in Tool
Engineers, Handbook on the subject supply this definition:
"Jigs
physically limit and control (guide) the path of a cutting tool.
Fixtures do not guide the tool but allow it to find its own path."
Source: E H. Girardot and J. I. Karash,
"Jigs and Fixtures", Engineers'
Handbook New York:
McGraw-Hill Book
Company, Inc., 1949, page 1541
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The
New Standard Dictionary,
(1952) defines fixture as
Any
device,
constituting an essential element of a machine, which holds in position
either the work or the tool acting on the work. A fixture in serving
its purpose is generally dependent upon the action of the machine of
which it is a part, while the jig is not.
Source: Funk
& Wagnalls New Standard Dictionary
(New York: Funk and Wagnalls, 1952.
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Webster's
International Dictionary, 2nd Edition
Unabridged, (1952)
defines:
Jig;
A
contrivance fastened to or enclosing a piece of work,
and having hard steel surfaces
to guide a tool, as a drill, or to form a shield or template to work
to, as in tiling.
Webster's
International also
has this to say about fixture:
"(a) A device for supporting the work,
during machining, without guiding the cutting tools. (b) A similar
device, for holding parts in correct position during assembly or
testing."
Source: Webster's
New International Dictionary, 2nd Edition
Unabridged, 1952 Springfield, MA: C.
C.Merriam Company, 1952
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In
the 1947 book, Jig and Fixture Design,
Ewald L. Witzel et al explain the difference between the two
as follows:
A jig is a
special device which holds, or supports, or is placed on a
part to be machined. It is a production tool so made that it not only
locates and holds the workpiece, but it also guides the cutting tool as
the operation is per.. formed, Jigs are usually fitted with hardened
steel bushings for guiding drills or other cutting tools.
A fixture is a production tool used to locate accurately and to hold
securely one or more work-pieces so that the required machining
operations can be performed. A fixture should be securely fastened to
the table or the machine upon which the work is done. Though used
largely on milling machines, fixtures are also designed and used to
hold. work for various operations on most of the standard machine
tools. The main purpose of a fixture is to locate the work quickly and
accurately, support it properly, and hold it securely.
Source: Ewald L. Witzel et al, Jig
and
Fixture Design Albany, NY: Delmar, 1947, page 6.
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The definitions above apply to
the metal working industries, which suggests that the term is widely
used in that field.
In woodworking, however -- according to Kansas State Teachers College
master's student, James R'Leigh Bell -- as late as 1955, nothing can be
found in books that attempts "to define or clarify what is
meant by either of the words 'jig' or 'fixture' as these
terms are used
in woodworking literature."
To
get around this lack of definition, Bell seeks to derive a meaning of
jig in a woodworking context by analyzing the usage of jig in
woodworking literature.
In some instances, Bell found, the words are used
interchangeably, as if they had the
same meaning.
Bell's example is Milton Gunerman's 1950 How to
Operate Your Power Tools.
With the aid of a fixture, for
example, Gunerman illustrates the sanding the edges
of circles and
curves on a disk sander. Gunerman shows the fixture, and how to make
it, but in the process of his explanation, he uses jig
and fixture interchangeably.
Unlike
the devices used in the metal industries the term "jig", in
their shops, woodworkers often use it when they refer
to aid for a hand
tool. In the woodworking fields and/or the
school woodshops, users of jigs understand the word "jig" means a
device
which is used to hold, guide, or direct the work, or the tool, for a
hand or power machine. It is not fastened to the bench, the machine
table, or fence, but may move and act with the operative part of the
tool or machine.
A fixture may also hold, guide or direct the work or tool. The fixture
is fixed or fastened or held to the bench, the machine table, fence or
stationary part.
Either jigs or fixtures make it possible to do a given job better,
faster, more economically or safer,. A jig or fixture is not a complete
tool in itself but only becomes a part of a tool when it is performing
one or more of the specified objectives stated herein.
Sources: Milton
Gunerman How to
Operate Your Power Tools. (New
York: The Home Craftsman Publishing Corp, 1950, pages 95, 116, 119;
James R'Leigh Bell, Jigs and fixtures in the wood
shop, Pittsburg: Kansas State Teachers College,
1953. As
Wallace Kunkel points in How to Master the Radial
Saw, historically,
the Radial Arm Saw was designed as a production machine for use in
lumber yards, and cabinet shops, for builders and similar users;
however, because of its versatility and ease of operation, it is now
found in many home workshops as well. With
accessories and attachments, the Radial Arm Saw does Horizontal
Mortising, Molding, Drilling,
Sanding, Shaping, and
several other operations that involve the use of circular cutting
tools. Undoubtedly these accessories that are now part of a package
that most buyers include with purchase of a RAS started out as jigs,
developed by one individual woodworker with a problem that needed to be
solved. For
the Radial Arm Saw, the sanding mode is interesting, in that, before
the Performax Drum Sander appeared on the market, ? [name not known at
the moment, but working on it] first developed this drum sander in a
home shop operation -- I have memories of the ads in woodworking
magazines in the late 1970s and early 1980s. An excellent
example
of
the "bottom-up" nature -- as a "jig" developed in a woodworker's home
shop -- i.e., the invention of power tools in the woodworking
industry. First the Performax was patented as an attachment
for
the radial arm saw, and then,
finally, actually organizing into the Performax Drum Sander
Corporation
as a manufacturing operation in its own right. (I'll post more details
on the history of Performax later; the entry on WWW.OWWM.COM is
sketchy: http://www.owwm.com/MfgIndex/detail.asp?ID=631)
Sources:
Fred H Colvin, Jigs and
Fixtures: A Reference Book, Showing Many Types of Jigs and Fixtures in
Actual Use, and Suggestions for Various Cases.
1913; Cyril Donaldson and George H. LeCane, Tool
Design, (New York: Harper
and Brothers, 1943; Ewald L. Witzel et al, Jig and
Fixture Design Albany, NY: Delmar, 1947; Milton Gunerman How to
Operate Your Power Tools. (New
York: The Home Craftsman Publishing Corp, 1950;
James R'Leigh Bell, Jigs and fixtures in the wood
shop, Pittsburg: Kansas State Teachers College,
1953; R A
Salaman, Dictionary
of Woodworking Tools, 2d ed revised, New town, CT:
Taunton Press, 1989; Wallace Kunkel, How to Master the Radial Saw
privately printed, 1997;R.
J. Decristoforo, The Ultimate Woodshop Jig Book. Cincinnati:
Popular Woodworking, 1999. R.
J. Decristoforo,The Jigs
& Fixtures Bible Cincinnatti
Popular Woodworking Books, 2003
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