Report on Mechanical Lathe

In wood turning, metalworking, metal spinning, and glass working, a lathe is a machine tool which spins a block of material so that when abrasive, cutting, or deformation tools are applied to the block, it can be shaped to produce an object which has symmetry about an axis of rotation. Most suitably equipped metalworking lathes can also be used to produce most solids of rotation, plane surfaces and screw threads or helices. Ornamental lathes can produce three-dimensional solids of incredible complexity. The material is held in place by either one or two centers, at least one of which can be moved horizontally to accommodate varying material lengths. Examples of objects that can be produced on a lathe include candlestick holders, cue sticks, table legs, bowls, baseball bats, crankshafts and camshafts.

Major categories of lathes
Woodworking lathes
Woodworking lathes are the oldest variety. All other varieties are descended from these simple lathes. An adjustable horizontal metal rail between the material and the operator accommodates the positioning of shaping tools, which are usually hand-held. With wood, it is common practice to press and slide sandpaper against the still-spinning object after shaping to smooth the surface.

Metalworking lathes
In a metalworking lathe, metal is removed from the workpiece using a hardened cutting tool, which is usually fixed to a solid moveable mounting called the “toolpost”, which is then moved against the workpiece using handwheels and/or computer controlled motors.


Metalworking lathes are commonly provided with a variable ratio gear train to drive the main leadscrew. This enables different pitches of threads to be cut. Some older gear trains are changed manually by using interchangeable gears with various numbers of teeth, while more modern or elaborate lathes have a quick change box to provide commonly used ratios by the operation of a lever.


Ornamental turning lathes
The ornamental turning lathe was developed around the same time as the industrial screwcutting lathe in the nineteenth century. It was used not for making practical objects, but for decorative work – ornamental turning. By using accessories such as the horizontal and vertical cutting frames, elliptical chuck and rose engine, solids of extraordinary complexity may be produced by various generative procedures. As well as a wide range of accessories, these lathes usually have complex dividing arrangements to allow the exact rotation of the mandrel.


Metal spinning lathes


Cue lathes

Glassworking lathes
In diamond turning, a computer-controlled lathe with a diamond-tipped tool is used to make precision optical surfaces in glass or other optical materials. Unlike conventional optical polishing, complex aspheric surfaces can be machined.

Watchmaker’s Lathes

Parts of a lathe
All lathes have a “bed”, which is (almost always) a horizontal beam (although some CNC lathes have a vertical beam for bed to ensure that swarf, or chips, falls free of the bed.
At one end of the bed (almost always the left, as the operator faces the lathe) is a “headstock”. The headstock contains high-precision spinning bearings.

Rotating within the bearings is a horizontal axle, with an axis parallel to the bed, called the “spindle”. Spindles are often hollow, and have exterior threads and/or an interior Morse taper on the “inboard” (i.e., facing to the right / towards the bed) by which accessories which hold the workpiece may be mounted to the spindle. Spindles may also have exterior threads and/or an interior taper at their “outboard” (i.e., facing away from the bed) end, and/or may have a handwheel or other accessory mechanism on their outboard end. Spindles are powered, and impart motion to the workpiece.

The spindle is driven, either by foot power from a treadle and flywheel or by a belt drive to a power source. In some modern lathes this power source is an integral electric motor, often either in the headstock, to the left of the headstock, or beneath the headstock, concealed in the stand. (An interesting note: Some Amish are known to purchase very high tech lathes, remove the electric motor, and then convert them to run via leather belts from an overhead line shaft.)
At the other end of the bed (almost always the right, as the operator faces the lathe) may be a tailstock. Not all lathes have tailstocks. A tailstock provides auxiliary support to the workpiece. Tailstocks are not powered.
Metalworking lathes have a “cross slide”, which is a flat piece that sits crosswise on the bed, and can be cranked at right angles to the bed. Sitting atop the cross slide is a toolpost, which holds a cutting tool which removes material from the workpiece. There may or may not be a leadscrew, which moves the cross slide along the bed.
Woodturning and metal spinning lathes do not have cross slides, but have “banjos”, which are flat pieces that sit crosswise on the bed. The position of a banjo can be adjusted by hand; no gearing is involved. Ascending vertically from the banjo is a tool post, at the top of which is a horizontal “tool rest”. In woodturning, hand tools are braced against the tool rest and levered into the workpiece. In metal spinning, the further pin ascends vertically from the tool rest, and serves as a fulcrum against which tools may be levered into the workpiece.

If a tailstock is used, a dead center (which is non-rotating) may be used to support the workpiece, alternatively, a live center may be used to better advantage. A lathe carrier may also be employed when turning between centers.
A circular metal plate with even spaced holes around the periphery, mounted to the spindle, is called an “index plate”. It can be used to rotate the spindle a precise number of degrees, then lock it in place, facilitating repeated auxiliary operations done to the workpiece.

Modes of use
When a workpiece is fixed between the headstock and the tailstock, it is said to be “between centers”. When a workpiece is supported at both ends, it is more stable, and more force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, without fear that the workpiece may break loose.
When a workpiece is fixed only to the spindle at the headstock end, the work is said to be “face work”. When a workpiece is supported in this manner, less force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, lest the workpiece rip free. Thus, most work must be done axially, towards the headstock, or at right angles, but gently.
When a workpiece is mounted with a certain axis of rotation, worked, then remounted with a new axis of rotation, this is referred to as “eccentric turning” or “multi axis turning”. The result is that various cross sections of the workpiece are rotationally symmetric, but the workpiece as a whole is not rotationally symmetric. This technique is used for camshafts, various types of chair legs, etc.

The smallest lathes are “jewelers lathes” or “watchmaker lathes”, which are small enough that they may be held in one hand. Although the workpieces machined on a jeweler’s lathes are metal, jeweler’s lathes differ from all other metal working lathes in that the cutting tools (called “gravers”) are hand held, supported by a T-rest, not fixed to a cross slide. The work is usually held in a collet and two spindle bores to receive such collets are common, namely 6mm and 8mm. Two patterns of bed are common, the WW (Webster Whitcomb) bed, which is found only on 8mm Watchmakers lathes which is a truncated triangular prism and the continental D-style bar bed used on both 6mm and 8mm lathes by firms such as Lorch and Star. Other designs have been used, e.g. Boley used a triangular prism as bed on some 6.5mm lathes, and IME used a V edged bed on their 8mm lathes.
Lathes that sit on a bench or table are called “bench lathes”.
Lathes that are controlled by a computer are CNC lathes.
Lathes with a vertical axis are — not surprisingly — “vertical lathes”.
A lathe with a cylindrical tailstock that can rotate around a vertical axis, so as to present different facets towards the headstock (and the workpiece) are turret lathes.
Various combinations are possible: e.g. one could have a “vertical CNC lathe”, etc.
Lathes can be combined with other mechanisms into more complex machines, such as those with an overhead drill or vertical milling unit. These are usually referred to as combination lathes.