Machine Tool
Machine tool is the name for the powered machines that shape metal and other rigid materials by removing material from them — the lathes, milling machines, drilling machines, grinders and their modern computer-controlled descendants that this site’s CNC machining subject runs on. The term is precise in a way that matters: not every machine that works metal is a machine tool, but the machine tool is the one built to a different standard, rigid enough to resist the forces of cutting and accurate enough to hold the sizes its parts must meet. Machine tools are the machines that make machines — the mother machines of manufacturing, the tools that produce the spindles, the bearings, the moulds and the mechanisms that every other industry then uses to make its products. When a part is machined, it is machined on a machine tool, and the machine tool is where the whole craft of this wiki begins and ends. This entry sets out what makes a machine a machine tool, the families into which they fall, and what they hold in common.
What makes a machine a machine tool
Three qualities mark a machine tool and separate it from the rest of the machinery that moves material. The first is controlled relative motion: a machine tool holds either the cutting tool or the work — usually both — and moves one against the other along precise, repeatable paths, so the shape of the part is written by the machine’s guidance rather than by the operator’s arm. The second is rigidity: cutting metal presses hard against the tool and the work, and a machine tool is built massive and stiff enough to resist those forces without flexing, because a machine that flexes prints its flexibility into every part it makes. The third is accuracy: the slides, spindles and measuring systems of a machine tool are made and aligned to far finer limits than the parts it will make, so that the machine’s errors are small next to the tolerances it is asked to hold. Put the three together and the definition is complete — a machine tool is a rigid, accurate machine that shapes material by moving a cutting edge against it under control — and the definition explains why machine tools are among the most carefully built machines in industry: they must be better than the parts they make, and the parts they make are better than almost everything else.
The great families
The machine tools of a workshop divide into families by the motion they use to cut, and every process in this wiki belongs to one of them. The turning family — the lathes and turning machines — holds the work in a rotating spindle and moves a single-point tool against it, generating round shapes: shafts, bores, threads and faces, the family this wiki treats under the turning process. The milling family — the milling machines and machining centres — holds the work on a table and drives a rotating multi-tooth cutter into it, generating flat surfaces, slots, pockets and complex 3-D forms. The drilling family adds the round holes that turning and milling then refine, the grinding family finishes hard or accurate surfaces with an abrasive wheel, and the erosion family — the EDM and wire machines — removes metal by spark rather than by cutting edge, for shapes no cutter can reach. Beyond the cutting families stand the presses, the forging and forming machines that shape metal by force rather than removal — often called machine tools in the broad sense but distinct from the machining families this site covers, which all work by taking material away.
What every machine tool holds in common
Look past the families and every machine tool is assembled from the same organs, and this wiki treats each in its own entry. There is the structure — the bed, the base and the column that carry every other part and supply the rigidity the machine lives on, the subject of this wiki’s entry on machine structure and rigidity. There is the spindle or the workhead that rotates the tool or the work, with its bearings and its drive — the spindle that turns at the speeds the cut needs. There are the slides and the drives that move the axes — the ball screws and linear motors that position the tool to the machine’s accuracy. There is the tooling interface that holds the cutter, and there is, on the modern machine, the control that directs all of it. On the manual machine tool each of these organs answers to a hand at a wheel; on the CNC machine tool they answer to a program, and the machine executes the coordinated motions that the manual machinist once made by eye and feel.
The machine tool as the measure of a shop
Because the machine tool is built better than the parts it makes, the capability of a shop is largely the capability of its machine tools: the accuracy a shop can offer is bounded by the accuracy of its machines, the size of its work by their envelopes, and its speed by their power and their rigidity. That is why the machine tool is such a consequential investment — it is the capital that the shop’s skill is applied through, and why the choices this wiki describes, from the type of machine to the condition of its ways, matter so much to the parts that come off it. A good machinist on an indifferent machine is limited by the machine; a good machine in skilled hands is where the tolerances on a drawing become parts that meet them. In the end the machine tool is the fixed point of machining — the rigid, accurate, powered machine that has shaped metal for two centuries and now, under numerical control, shapes it with a fidelity no hand could match. Every entry in this wiki — the cutting, the tools, the workholding, the programming — is an entry about what happens on and around a machine tool, and the machine tool is where the drawing becomes the part.