Lathe
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This article is about a lathe as a tool. See also lathe (graphics) and lathe (division) for other meanings.
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In woodturning, metalworking, metalspinning, and glassworking, 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 rotational symmetry about an axis of rotation. Examples of objects that can be produced on a lathe include candlestick holders, table legs, bowls, baseball bats, crankshafts or camshafts.
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. An adjustable horizontal metal rail between the material and the operator accommodates the positioning of shaping tools. With wood, it is common practice to press and slide sandpaper against the still-spinning object after shaping.
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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.
In metalspinning, a disk of sheet metal is held perpendicularly to the main axis of the lathe, and tools with polished tips areare hand held, but levered by hand against fixed posts, to develop large amounts of torque/pressure that deform the spinning sheet of metal.
In a woodworking lathe most tools are hand held.
In a glassworking lathe a torch to soften the glass may be either hand-held, or mounted to a banjo/crossslide. Tools to deform the glass, and tubes to blow (inflate) the glass are usually handheld.
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Major Categories of Lathes
Woodworking Lathes
Woodworking lathes are the oldest variety of lathes. All other varieties are descended from these simple lathes.
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Metalspinning Lathes
Metalspinning lathes are almost as simple as woodturning lathes. Metalspinning lathes require a user-supplied rotationally symmetric pattern, usually made of wood, which serves as a template onto which the workpiece is moulded. E.g.: If you want to make a sheetmetal bowl, you need a solid chunk of wood in the shape of the bowl; if you want to make a vase, you need a solid template of a vase, etc.
Given the advent of high speed, high pressure, industrial die forming, metalspinning is less common now than it once was.
Metalworking Lathes
The toolpost is manually operated by a leadscrew to position the tool in a variety of planes. The toolpost may also be automatically driven to produce automatic finishing of a piece, or for cutting threads, gears, etc. Cutting fluid may also be pumped to the cutting site to provide cooling, lubrication and clearing of swarf from the workpiece. Some lathes may be operated under control of a computer for mass production of parts (see "Computer Numerically Controlled", or CNC).
The workpiece may be supported between a pair of hardened points called centres, or it may be bolted to a faceplate or held in a chuck. A chuck has movable jaws that can grip the workpiece. For a metal lathe, the tool is situated in the toolpost which sits on the cross slide which is on the saddle. The saddle moves along the axis of the workpiece, and the cross slide moves perpendicular to the axis. The movements are normally calibrated so that precise cuts can be made. An additional slide called a topslide is often present, and this can be angled to permit cutting short tapers. A screwcutting lathe has provision for gearing the feed along the axis to the drive rotating the workpiece. Suitable choice of ratios permits screw threads to be cut and also allows for an automatic fine feed. This allows the operator to stand and watch. With ingenuity, a lathe can perform many diverse machining tasks, although the size of work may be limited compared to special machines.
Glassworking Lathes
Glassworking lathes are similar in design to other lathes, but differ markedly in how the workpiece is modified. Glassworking lathes slowly rotate a hollow glass vessel over a fixed or variable temperature flame. The source of the flame may be moved along the lathe bed. The flame serves to soften the glass being worked, so that the glass in a specific area of the workpiece beomes malleable, and subject to forming either by inflation ("glass blowing"), or by deformation with a heat resistant tool.
Parts Of a Lathe
A lathe may or may not have a stand (or legs), which sits on the floor and elevates the lathe bed to a working height. Some lathes are small and sit directly on a workbench or table, and do not have a stand.
All lathes have a "bed", which is an (almost always) horizontal beam.
At one end of the bed (almost always the left, as the operator faces the lathe) is a "headstock". The headstock contains a 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 accessor mechanism on their outboard end. Spindles are powered, and impart motion to the workpiece.
The spindle is driven, either by footpower, by a belt to an external power source, or by 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 motors, and then convert them to run via leather belts from overhead power shafts.)
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 auxillary 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 metalspinning 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 toolpost, 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 metalspinning, the further pin ascends vertically from the tool rest, and serves as a fulcrum against which tools may be levered into the workpiece.
Accessories
Unless a workpiece has a taper machined onto it which perfectly matches the internal taper in the spindle, or has threads which perfectly match the external threads on the spindle (two things which almost never happen), an accessory must be used to mount a workpiece to the spindle.
A wooden or metal workpiece may be bolted or screwed to a "faceplate", a large flat disk that mounts to the spindle.
A wooden workpiece may be pinched between centers by using a "spur drive" at the headstock, which bites into the wood and imparts torque to it.
A wooden or metal workpiece may be camped in a three or four jaw chuck, which mounts to the spindle.
If a tailstock is used, a "dead center", which is a non-rotating cone of metal that mounts in the tailstock, may be used to support the tail of the workpiece. When used on a metalworking lathe, dead centers have the slight problem that they cause friction against the workpiece, causing the workpiece to heat, which causes the workpiece to expand, which increases the pressure against the dead center. Thus, the operator must oil and monitor the dead center as he works.
Alternatively, a "live center", which is a cone of metal that rotates on bearings, may be used to support the tail of the workpiece. In woodturning, one subtype of a live center is a "cup center", which is a cone of metal surrounded by an anullar ring of metal, which decreases splitting of the workpiece.
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 auxillary 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, with out 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 worpiece 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 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 cam shafts, various types of chair legs, etc.
Varieties
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, not fixed to a crossslide.
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 suprisingly—"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".
A lathe equipped with indexing plates, profiled cutters, spiral or helical guides, etc. so as to enable ornamental turning is an "ornamental lathe".
Various combinations are possible: e.g. one could have a "vertical CNC lathe", etc.
See also
External links
History
- Medieval and Renaissance Lathes: http://www.his.com/~tom/sca/lathes.html
- The development of the lathe: http://www.stuartking.co.uk/articles/lathe.htm
- Early Wood-Working: http://www.regia.org/woodwork.htm
- Spring pole lathe: http://www.historicgames.com/lathes/springpole.html
- Lathes CNC and Manual: http://www.machinetools.btinternet.co.uk
- Introduction to Metal Spinning on Manual and Automatic CNC Lathes (http://www.franjometal.com/metal-spinning/intro-metal-spinning.html)
- On ye art and mystery of Turning (http://homepages.ihug.com.au/~dispater/turning.htm)
Instruction/Support
- Instructional video rental: metal working lathes (http://technicalvideorental.com/rental_12.html), wood working lathes (http://technicalvideorental.com/rental_28.html)
- Lathes and other small machine tools for the enthusiast and professional: http://www.lathes.co.uk/index.html
- 7x10, 7x12 and 7x14 Asian mini-lathes: http://www.mini-lathe.com/
- Hand Metal Spinning and CNC Metal Spinning Lathe Video Demonstrations (http://www.franjometal.com/metal-spinning/spinning-videos.html)
Important Books
Turning Wood With Richard Raffan 1561584177
Vendors: Woodworking Lathes
- Delta (http://www.deltawoodworking.com/)
- JET (http://www.wmhtoolgroup.com/index.cfm?area=shop&action=vendors&VID=1)
- Powermatic (http://www.wmhtoolgroup.com/index.cfm?area=shop&action=vendors&VID=2)
- Oneway (http://www.oneway.on.ca/)
Vendors: Metalworking Lathes
- Sherline (http://www.sherline.com/)
- South Bend (http://www.southbendlathe.com/)
- Bridgeport (http://www.bpt.com/)
- Used Lathes (http://www.machinetools.btinternet.co.uk/)de:Drehmaschine
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