Editing Machine tool (section)

==Nomenclature and key concepts, interrelated==
{{More citations needed section|date=February 2021}}

Many [[history of technology|historians of technology]] consider that true machine tools were born when the toolpath first became guided by the machine itself in some way, at least to some extent, so that direct, [[wikt:freehand#Adjective|freehand]] human guidance of the toolpath (with hands, feet, or mouth) was no longer the only guidance used in the cutting or forming process. In this view of the definition, the term, arising at a time when all tools up till then had been [[hand tool]]s, simply provided a label for "tools that were machines instead of hand tools". Early [[lathe]]s, those prior to the late [[medieval]] period, and modern woodworking lathes and [[potter's wheel]]s may or may not fall under this definition, depending on how one views the headstock [[spindle (tool)|spindle]] itself; but the earliest historical records of a lathe with direct mechanical control ''of the cutting tool's path'' are of a screw-cutting lathe dating to about 1483.<ref name="Moore1970p137">{{Harvnb|Moore|1970|p=137, figure 213}}.</ref> This lathe "produced screw threads out of wood and employed a true compound slide rest".<ref name="Moore1970p137"/>

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The mechanical toolpath guidance grew out of various root concepts:{{or}}
* First is the [[spindle (tool)|spindle]] concept itself, which constrains workpiece or tool movement to [[rotation around a fixed axis]]. This ancient concept predates machine tools per se; the earliest lathes and [[potter's wheel]]s incorporated it for the workpiece, but the movement of the tool itself on these machines was entirely freehand.
* The machine slide ([[Tool Ways|tool way]]), which has many forms, such as dovetail ways, box ways, or cylindrical column ways. Machine slides constrain tool or workpiece movement [[wikt:linear#Adjective|linearly]]. If a stop is added, the ''length'' of the line can also be accurately controlled. (Machine slides are essentially a subset of [[linear bearing]]s, although the language used to classify these various [[machine element]]s may be defined differently by some users in some contexts, and some elements may be distinguished by contrasting with others)
* Tracing, which involves following the contours of a model or template and transferring the resulting motion to the toolpath.
* [[Cam (mechanism)|cam]] operation, which is related in principle to tracing but can be a step or two removed from the traced element's matching the reproduced element's final shape. For example, several cams, no one of which directly matches the desired output shape, can actuate a complex toolpath by creating component [[Euclidean vector|vectors]] that add up to a net toolpath.
* [[Van der Waals force|Van Der Waals Force]] between like materials is high; freehand manufacture of square plates, produces only square, flat, machine tool building reference components, accurate to millionths of an inch, but of nearly no variety. The process of feature replication allows the flatness and squareness of a milling machine cross slide assembly, or the roundness, lack of taper, and squareness of the two axes of a lathe machine to be transferred to a machined work piece with accuracy and precision better than a thousandth of an inch, not as fine as millionths of an inch. As the fit between sliding parts of a made product, machine, or machine tool approaches this critical thousandth of an inch measurement, lubrication and capillary action combine to prevent Van Der Waals force from welding like metals together, extending the lubricated life of sliding parts by a factor of thousands to millions; the disaster of oil depletion in the conventional automotive engine is an accessible demonstration of the need, and in aerospace design, like-to-unlike design is used along with solid lubricants to prevent Van Der Waals welding from destroying mating surfaces. Given the modulus of elasticity of metals, the range of fit tolerances near one thousandth of an inch correlates to the relevant range of constraint between at one extreme, permanent assembly of two mating parts and at the other, a free sliding fit of those same two parts.

Abstractly programmable toolpath guidance began with mechanical solutions, such as in [[musical box]] cams and [[Jacquard loom]]s. The [[technological convergence|convergence]] of programmable mechanical control with machine tool toolpath control was delayed many decades, in part because the programmable control methods of musical boxes and looms lacked the rigidity for machine tool toolpaths. Later, electromechanical solutions (such as [[servomechanism|servos]]) and soon electronic solutions (including [[computer]]s) were added, leading to [[numerical control|numerical control and computer numerical control]].

When considering the difference between freehand toolpaths and machine-constrained toolpaths, the concepts of [[accuracy and precision]], [[efficiency]], and [[productivity]] become important in understanding ''why'' the machine-constrained option adds [[value (economics)|value]].

Matter-Additive, Matter-Preserving, and Matter-Subtractive "Manufacturing" can proceed in sixteen ways: Firstly, the work may be held either in a hand, or a clamp; secondly, the tool may be held either in a hand, or a clamp; thirdly, the energy can come from either the hand(s) holding the tool and/or the work, or from some external source, including for examples a foot treadle by the same worker, or a motor, without limitation; and finally,  the control can come from either the hand(s) holding the tool and/or the work, or from some other source, including computer numerical control. With two choices for each of four parameters, the types are enumerated to sixteen types of Manufacturing, where Matter-Additive might mean painting on canvas as readily as it might mean 3D printing under computer control, Matter-Preserving might mean forging at the coal fire as readily as stamping license plates, and Matter-Subtracting might mean casually whittling a pencil point as readily as it might mean precision grinding the final form of a laser deposited turbine blade.

A precise description of what a machine tool is and does in an instant moment is given by a 12 component vector relating the linear and rotational degrees of freedom of the single work piece and the single tool contacting that work piece in any machine arbitrarily and in order to visualize this vector it makes sense to arrange it in four rows of three columns with labels x y and z on the columns and labels spin and move on the rows, with those two labels repeated one more time to make a total of four rows so that the first row might be labeled spin work, the second row might be labeled move work, the third row might be labeled spin tool, and the fourth row might be labeled move tool although the position of the labels is arbitrary which is to say there is no agreement in the literature of mechanical engineering on what order these labels should be but there are 12 degrees of freedom in a machine tool. That said it is important to remember that this is in an instant moment and that instant moment may be a preparatory moment before a tool makes contact with a work piece, or maybe an engaged moment during which contact with work and tool requires an input of rather large amounts of power to get work done which is why machine tools are large and heavy and stiff. Since what these vectors describe our instant moments of degrees of freedom the vector structure is capable of expressing the changing mode of a machine tool as well as expressing its fundamental structure in the following way: imagine a lathe spending a cylinder on a horizontal axis with a tool ready to cut a face on that cylinder in some preparatory moment. What the operator of such a lathe would do is lock the x-axis on the carriage of the lathe establishing a new vector condition with a zero in the x slide position for the tool. Then the operator would unlock the y-axis on the cross slide of the lathe, assuming that our examples were equipped with that, and then the operator would apply some method of traversing the facing tool across the face of the cylinder being cut and a depth combined with the rotational speed selected which engages cutting ability within the power of range of the motor powering the lathe. So the answer to what a machine tool is, is a very simple answer but it is highly technical and is unrelated to the history of machine tools.

Preceding, there is an answer for what machine tools are. We may consider what they do also. Machine tools produce finished surfaces. They may produce any finish from an arbitrary degree of very rough work to a specular optical grade finish the improvement of which is moot. Machine tools produce the surfaces comprising the features of machine parts by removing chips. These chips may be very rough or even as fine as dust. Every machine tools supports its removal process with a stiff, redundant and so vibration resisting structure because each chip is removed in a semi a synchronous way, creating multiple opportunities for vibration to interfere with precision.

Humans are generally quite talented in their freehand movements; the drawings, paintings, and [[sculpture]]s of artists such as [[Michelangelo]] or [[Leonardo da Vinci]], and of countless other talented people, show that human freehand toolpath has great potential. The [[value (economics)|value]] that machine tools added to these human talents is in the areas of rigidity (constraining the toolpath despite thousands of [[newton (unit)|newtons]] ([[pound-force|pounds]]) of force fighting against the constraint), [[accuracy and precision]], [[efficiency]], and [[productivity]]. With a machine tool, toolpaths that no human muscle could constrain can be constrained; and toolpaths that are technically possible with freehand methods, but would require tremendous time and skill to execute, can instead be executed quickly and easily, even by people with little freehand talent (because the machine takes care of it). The latter aspect of machine tools is often referred to by historians of bytechnology as "building the skill into the tool", in contrast to the toolpath-constraining skill being in the ''person'' who wields the tool. As an example, it is ''physically possible'' to make [[interchangeable parts|interchangeable]] screws, bolts, and nuts entirely with freehand toolpaths. But it is ''economically practical'' to make them only with machine tools.-->
In the 1930s, the U.S. National Bureau of Economic Research (NBER) referenced the definition of a machine tool as "any machine operating by other than hand power which employs a tool to work on metal".<ref name="Jerome1934">{{Harvnb|Jerome|1934|p=178, Ch. 4, Note 75}}.</ref>

The narrowest [[colloquial]] sense of the term reserves it only for machines that perform metal cutting—in other words, the many kinds of conventional [[machining]] and [[grinding (abrasive cutting)|grinding]]. These processes are a type of deformation that produces [[swarf]]. However, [[economist]]s use a slightly broader sense that also includes metal deformation of other types that squeeze the metal into shape without cutting off swarf, such as rolling, stamping with [[die (manufacturing)|dies]], shearing, [[swaging]], [[rivet]]ing, and others. Thus [[machine press|presses]] are usually included in the economic definition of machine tools. For example, this is the breadth of definition used by [[Max Holland]] in his history of Burgmaster and [[Houdaille Industries|Houdaille]],<ref name="Holland1989">{{Harvnb|Holland|1989}}.{{page needed|date=April 2025}}</ref>{{page needed|date=April 2025}} which is also a history of the machine tool industry in general from the 1940s through the 1980s; he was reflecting the sense of the term used by Houdaille itself and other firms in the industry. Many reports on machine tool [[export]] and [[import]] and similar economic topics use this broader definition.

The colloquial sense implying conventional metal cutting is also growing obsolete because of changing technology over the decades. The many more recently developed processes labeled "machining", such as [[electrical discharge machining]], [[electrochemical machining]], [[electron beam machining]], [[photochemical machining]], and [[ultrasonic machining]], or even [[plasma cutting]] and [[water jet cutter|water jet cutting]], are often performed by machines that could most logically be called machine tools. In addition, some of the newly developed [[additive manufacturing]] processes, which are not about cutting away material but rather about adding it, are done by machines that are likely to end up labeled, in some cases, as machine tools. In fact, [[machine tool builder]]s are already developing machines that include both [[subtractive manufacturing|subtractive]] and [[additive manufacturing]] in one work envelope,<ref name="Zelinski_2013-11-08">{{Citation |last=Zelinski |first=Peter |date=2013-11-08 |title=Hybrid machine combines milling and additive manufacturing |journal=[[Modern Machine Shop]] |url=http://www.mmsonline.com/blog/post/hybrid-machine-combines-milling-and-additive-manufacturing |postscript=.}}</ref> and retrofits of existing machines are underway.<ref name="Zelinski_2014-02-21">{{Citation |last=Zelinski |first=Peter |date=2014-02-21 |title=The capacity to build 3D metal forms is a retrofittable option for subtractive CNC machine tools |journal=Modern Machine Shop Additive Manufacturing Supplement |url=http://www.additivemanufacturinginsight.com/articles/add-on-additive-manufacturing |postscript=.}}</ref>
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The [[natural language]] use of the terms varies, with subtle [[connotation|connotative]] boundaries. Many speakers resist using the term "machine tool" to refer to [[woodworking machine]]ry (joiners, table saws, routing stations, and so on), but it is difficult to maintain any true logical dividing line, and therefore many speakers accept a broad definition. It is common to hear machinists refer to their machine tools simply as "machines". Usually the [[mass noun]] "machinery" encompasses them, but sometimes it is used to imply only those machines that are being excluded from the definition of "machine tool". This is why the machines in a food-processing plant, such as conveyors, mixers, vessels, dividers, and so on, may be labeled "machinery", while the machines in the factory's tool and die department are instead called "machine tools" in contradistinction.

Regarding the 1930s NBER definition quoted above, one could argue that its specificity to metal is obsolete, as it is quite common today for particular lathes, milling machines, and machining centers (definitely machine tools) to work exclusively on plastic cutting jobs throughout their whole working lifespan. Thus the NBER definition above could be expanded to say "which employs a tool to work on metal ''or other materials of high hardness''". And its specificity to "operating by other than hand power" is also problematic, as machine tools can be powered by people if appropriately set up, such as with a [[treadle]] (for a [[lathe]]) or a hand lever (for a [[shaper]]). Hand-powered shapers are clearly "the 'same thing' as shapers with electric motors except smaller", and it is trivial to power a [[micro lathe]] with a hand-cranked belt pulley instead of an electric motor. Thus one can question whether power source is truly a key distinguishing concept; but for economics purposes, the NBER's definition made sense, because most of the commercial value of the existence of machine tools comes about via those that are powered by electricity, hydraulics, and so on. Such are the vagaries of [[natural language]] and [[controlled vocabulary]], both of which have their places in the business world.-->