Mini Lathe Introduction
If you are new to metalworking lathes and lathe work, this page will help you understand some of the basic concepts, terminology and capabilities. In essence, a lathe, whether for woodworking or metalworking, rotates a cylindrical workpiece along its axis and removes material from the workpiece to form it into a specific shape.
On a woodworking lathe, the cutting tools usually are hand-held against a support and are moved in and out and back and forth along the surface of the work by hand to form a shape such as a table leg.
On metalworking lathes, the cutting tools are held rigidly in a tool holder that is mounted on a movable platform called the carriage. The tool is moved in and out by means of hand wheels and back and forth either by turning a handwheel or under power from the lathe. The result is that material can be removed from the workpiece under very precise control to produce shapes that are truly precision made.
Dimensional accuracies of one-one-thousandth of an inch (.001″) or one-tenth of a millimeter are typical. Because of the inherent rotational nature of a lathe, the vast majority of the work produced on it is basically cylindrical in form. In spite of this, the lathe is an extremely versatile machine capable of producing a surprising variety of objects used mainly as component parts of mechanical systems.
To gain a good understanding of the lathe, you will need to know the names of the various components, as illustrated below.
The carriage, in the circled area, consists of the apron, the vertical casting on which the carriage handwheel is mounted, and the saddle (not shown), the H-shaped casting that rides on the ways to which the apron is attached.
When comparing the size and working capacities of metal lathes there are several key dimensions to consider:
Swing over bed: The diameter of the largest workpiece that can be rotated on the spindle without hitting the bed. This is the first of the two numbers used to describe the size of a metal lathe. In the case of the 7×10 or 7×12 lathes, it is 7″.
Distance between centers: The longest piece of work that be held between a center in the headstock and a center in the tailstock. (see glossary below for more information). This is the second of the two numbers used to describe the lathe size. Based on this you would expect that a 7×10 would accommodate 10″ between centers, a 7×12, 12″ and a 7×14, 14″. In fact, due to wishful marketing, the 7×10 is really only a 7×8. The 7×12 and 7×14 are what you would expect them to be.
Swing over the carriage: The diameter of the largest workpiece that can rotate over the carriage without hitting it. On the 7x lathes this is about 4″
Diameter of spindle through-hole: The diameter of the hole that passes through the spindle. On the 7x lathes (or any lathe having a #3 Morse Taper spindle) it is about 3/4″. When facing relatively long stock, the free end of the stock can pass through the spindle if it is no larger than the through-hole diameter.
Here’s a table summarizing some of the dimensions for a 7×12 and 9×20 lathe:
|Swing Over Bed
|Distance Between Centers
|Swing Over Carriage
|Spindle Through-Hole Diameter
Glossary of Lathe and Mill Terms
Apron: Front part of the carriage assembly on which the carriage handwheel is mounted.
Bed: Main supporting casting running the length of the lathe.
Between Centers: 1. A method of holding a workpiece by mounting it between a center in the headstock spindle and a center in the tailstock spindle (see Center). The workpiece is gripped and driven by a dog.
2. A dimension representing the maximum length of a workpiece that can be turned between centers. A 7×10 lathe is 10″ between centers; a 7×12 lathe is 12″ between centers. Since longer is generally better, lathe vendors sometimes overstate this number.
Bit: A sharpened cutting tool, such as a drill bit or lathe bit, used to remove metal or other material from a workpiece.
Carbide: An extremely hard, heat- and wear-resistant material used for making cutting tools. In the context of machine tools, usually refers to tungsten carbide. While very hard, it is brittle and subject to chipping under impact.
Carriage: Assembly that moves the toolpost and cutting tool along the ways.
Carriage Handwheel: A wheel with a handle used to move the carriage by hand by means of a rack and pinion drive.
Carriage Lock: A mechanism for locking the carriage to the ways so that the saddle does not move along the ways during facing operations. A standard feature on most larger lathes, but not on the mini lathe. Easy to add, though.
Casting: A metal component formed into a specific shape by pouring molten metal into a hollow form of the desired shape. After the metal cools and solidifies, the shaped casting is removed from the form and excess metal, known as flashing, is removed.
The form typically is made from a specialized mixture of sand and binding agent and is divided into two halves that are separated to remove the finished casting. May also refer to the process of producing a casting.
The casting process is used to manufacture most of the large metal components of machine tools. The rough cast components are machined by machine tools to form precision mating surfaces such as the ways of a lathe or the table of a milling machine.
Center: A precision ground tapered cylinder with a 60º pointed tip and a Morse Taper shaft. Held in the lathe tailstock to support the end of a long workpiece. May also be used in the headstock spindle to support work between centers at both ends. Also the process of positioning a workpiece accurately in line with a drill or mill.
A live center is a center with integral bearings to reduce friction; a dead center has no bearings, so the tip must be kept lubricated to keep the center and workpiece from overheating due to friction.
As a verb – To accurately position a workpiece so that the center of the workpiece, or the center of a feature such as a hole, is concentric with a the lathe centerline or the spindle of a milling machine. May also apply to centering a rotary table or other work holding device concentric with the milling machine spindle.
Center Drill: 1. A short, stubby drill used to form a pilot hole for drilling and a shallow countersunk hole for mounting the end of a workpiece on a center.
2. The process of drilling a workpiece with a center drill
Centerline: An imaginary line extending from the center of the spindle through the center of the tailstock ram, representing the central axis of the lathe around which the work rotates.
Chuck: A clamping device for holding work in the lathe or for holding drills in the tailstock. Drill chucks are sometimes referred to as Jacobs Chucks, a brand name that popularized that style of chuck.
Compound: Movable platform on which the toolpost is mounted; can be set at an angle to the workpiece. Also known as the compound slide and compound rest.
Compound Handwheel: A wheel with a handle used to move the compound slide in and out. Also known as the compound feed.
Counterbore: 1. To drill a shallow flat-bottomed hole slightly larger than and concentric with a previously drilled hole to allow the head of a screw to be sunk below the surface of a workpiece. A special counterbore tool or an end mill is used to drill the hole so that the bottom will be flat.
2. A hole drilled by this process.
Countersink: 1. To form a shallow, cone-shaped hole surrounding a smaller diameter drilled hole. A countersink is often used so that the head of a flat-head screw will be flush with, or slightly below, the surface in which the screw is being used.
2. A cutting tool, similar to a drill bit, with a cone-shaped tip, used to cut a countersink hole. Often combined with a short drill bit tip as a “combination drill and countersink”, or center drill.
Cross Feed: A handwheel or crank that moves the cross-slide by turning a screw. Also the action of moving the cross slide using the cross feed handwheel.
Cross Slide: Platform that moves perpendicular to the lathe axis under control of the cross-slide handwheel.
Cross-slide Handwheel: A wheel with a handle used to move the cross-slide in and out. Also known as the cross feed.
Cutting Tool: The tool that does the cutting, or removal of metal or other material. May refer to any type of cutting tool such as a drill, reamer or a lathe bit. A lathe bit typically has a square cross-section with a sharpened tip on one end. It is made from very hard and heat-resistant material such as High Speed Steel or a form of carbide.
Dead Center: A lathe center made from a solid piece of steel with no bearings, typically used to support the tailstock end of a relatively long, limber workpiece. Since there are no bearings, the tip must be well lubricated to keep it from heating up due to friction. See also: Live Center.
Dog: Also known as a Lathe Dog or Dogleg. An “L”-shaped adapter, usually made of cast iron, with a hole for the workpiece and locking screw to secure the workpiece. Used to clamp a workpiece and apply rotational force to it while the workpiece is mounted between centers along with a faceplate.
The dog engages with a hole in the faceplate to apply the force to the workpiece. Used in place of a chuck, especially in pre-1940’s work, and/or when tapers are cut by offsetting the tailstock.
Dovetail or Dovetail Slide: A sliding surface between two closely matched components on a machine tool such as a lathe cross-slide. The dovetail ensures that the two components can move in a precise linear motion with very little side-to-side motion.
So-named because it looks, in an end-on view, similar to the shape of a dove’s tail. Also a common type of joint used in woodworking and so-named for the same reason.
Faceplate: A metal plate with a flat face that is mounted on the lathe spindle to hold irregularly shaped work.
Facing: A lathe operation in which metal is removed from the end of workpiece to create a smooth perpendicular surface, or face. The cutting tool is moved across the ways by turning the cross-slide handwheel, aka cross-feed.
Gib: A length of steel or brass with a diamond-shaped cross-section that engages with one side of a dovetail and can be adjusted by means of screws to take up any slack in the dovetail slide. Used to adjust the dovetail for optimum tightness and to compensate for wear.
Halfnut or Half-nut: A nut formed from two halves which clamp around the leadscrew under control of the halfnut lever to move the carriage under power driven from the leadscrew. The halfnut commonly is 6-10 full threads in length to spread the driving force over a larger area.
Halfnut: Lever Lever to engage the carriage with the leadscrew to move the carriage under power.
Handwheel: A wheel turned by hand to move a component of a lathe or other machine tool. Often will have a handle extending from the front face. The handle facilitates rapid turning of the handwheel.
Headroom: The distance between the tip of the spindle (or chuck) and the table on a milling machine or drill press.
Headstock: The main casting mounted on the left end of the bed, in which the spindle is mounted. Houses the spindle speed change gears.
High Speed Steel (HSS): An alloy of steel used for cutting tools such as lathe bits and drill bits. HSS is highly-resistant to losing its hardness due to heating from friction. When used for lathe cutting bits, a HSS blank is ground to the desired shape on a bench grinder.
Interrupted Cut: A cutting operation on a lathe or mill in which the surface along which the cutting tool is moving has gaps or openings. The cutting action of the tool is thus “interrupted” each time it passes over such an opening.
Due to the vibration caused by this process, extra care must be taken to ensure that the cutting tool and the workpiece are securely mounted so that they don’t work loose. On a milling machine, the head must be securely locked in place so that it does not slip.
Jacobs Chuck: A common style of drill chuck that uses a geared outer ring along with a chuck key that engages with the geared ring to hold a drill bit very tightly. Prior to the introducion of “keyless” chucks, these were universally used on handheld power drills and drill presses. Jacobs is a trademarked brand name that is often used as a generic name for chucks of that style.
Jacobs Taper: One of several industry-standard specifications for tapered tool shanks. Tapered shafts on tools engage with a recess of matching taper in a lathe, drill press, milling machine spindle or on a rotary table or similar tools.
Tapers are precision-machined and when properly mated, and free from oil and grit, hold the tool tightly and concentric to the machine spindle. Once mated, tools held by a taper must be removed by forcing them free by driving a soft shaft in from the rear of the tool, using a hammer or screw to apply force.
Leadscrew: Precision screw that runs the length of the bed. Used to drive the carriage under power for turning and thread cutting operations. Smaller leadscrews are used within the cross-slide and compound to move those parts by precise amounts.
Industrial lathes have a separate drive for power feed and reserve the leadscrew for screw cutting to reduce unnecessary wear on the leadscrew.
Live Center: A lathe center with integral ball bearings that allow the tip to turn independently of the tapered end to reduce friction when using the center to support the end of the workpiece. See Dead Center.
Long Taper: A taper, cut on a lathe, that typically is too long to cut by offsetting the compound. On many lathes, the tailstock is formed from two components, the upper part of which can be offset relative to the lathe centerline.
The workpiece is center-drilled on both ends and supported between centers using a dog to drive the workpiece. The tailstock is offset to the desired angle of the taper. As the carriage moves along the ways, the cutting tool remains parallel to the lathe centerline, but the workpiece is cut along a taper because it is offset.
Industrial-class lathes sometimes have a taper attachment that allows for cutting long tapers without offsetting the tailstock. As the carriage moves along the ways, the taper attachment moves the cross-slide in or out at a constant rate, resulting in a tapered cut.
Machine Tool: A machine, such as a lathe, drill press or milling machine, designed to shape and form metal and other materials to a high degree of precision. Typical dimensional accuracies are on the order of thousandths of an inch or hundredths of a millimeter. Machine tools can range from desk-top size to huge machines weighing many tons used for industrial work.
Machining: The process of shaping metal or other material using a machine tool such as a lathe or milling machine. Most machining operations, such as drilling or turning, cut away excess material leaving the desired shape and dimensions.
Morse Taper: A taper of specific dimensions used to mate matching male and female parts such that they lock together tightly and concentrically. Tapers are of various sizes such as #0, #1, #2, #3, etc. with larger numbers representing larger sizes. The spindle of the mini-lathe has a #3 Morse Taper and the tailstock ram has a #2 Morse Taper.
Pilot Hole: A shallow hole, usually cone-shaped, drilled as a starter hole before drilling a deeper hole. The pilot hole helps to ensure that the drill bit enters the material at the desired location and does not drift or wander as the bit starts cutting into the material being drilled.
Quill: Part of a drill press, milling machine, lathe tailstock or other machine tool that extends from and retracts into a part of the machine under control of a hand lever or handwheel. Typically, the quill has an industry-standard taper to hold a chuck or other tool-holding device.
R8 Taper: An industry-standard taper most often used for the the spindle bore and tooling shanks of mid-sized milling machines. Tapered shanks ensure that machine tools are accurately concentric with the spindle and resist the sidewards forces imposed by milling operations.
R8 tapers are considered to be “self-releasing”, needing little or no force to break them free from the spindle when changing tools.
Rack and Pinion: A gear arrangement for moving a linear gear (rack) by turning a circular gear (pinion). Used to convert a rotating motion, typically of a handwheel, into a controlled linear motion. A typical example is the focusing mechanism on a microscope.
Saddle: A casting, often shaped like an “H” when viewed from above, that rides along the ways. Along with the apron, it is one of the two main components that make up the carriage.
Short Taper: A taper, cut on a lathe, which is sufficiently short in length that it can be cut by offsetting the compound to the desired angle of the taper.
Shoulder: The point at which a workpiece changes sharply from one diameter to another.
Spindle: Main rotating shaft on which the chuck or other work-holding device is mounted. It is mounted in precision bearings and passes through the headstock. In more general terms, the main rotating part of a machine tool.
Spindle Through-hole: A dimension indicating the minimum diameter of the hole that passes through the spindle. A workpiece with a diameter smaller than this can pass through the spindle to facilitate working on long pieces of work.
On the minilathe it is 3/4″ but can safely be reamed out to 13/16″. Note that near the front of the spindle the hole is tapered, to hold tapered tooling, and is larger than 3/4″ when looking at the spindle.
Stock: 1. The piece of metal or other material being machined in a lathe
2. Raw material such as metal rod that will be cut down to workable size and machined
Swing: A dimension representing the largest diameter workpiece that a lathe can rotate. The 7×10, 7×12 and 7×14 mini-lathes all have a 7″ swing, meaning that the maximum size workpiece that can rotate without hitting the bed is 7″ in diameter.
A related dimension, Swing Over Carriage or Swing Over Cross Slide, is the maximum diameter workpiece that can rotate over the cross slide. This is about 4″ on the 7x lathes, so any workpiece longer than about 3″ cannot be larger than 4″ diameter.
Tailstock: Cast iron assembly at the right end of a lathe that can slide along the ways and be locked in place. Used to hold long work in place or to mount a drill chuck for drilling into the end of the work.
Tailstock Handwheel: A wheel with a handle used to move the tailstock ram in and out of the tailstock casting.
Tailstock Ram: A piston-like shaft that can be moved in and out of the tailstock by turning the tailstock handwheel. Also known as the quill. Has a tapered internal bore to accept a Morse Taper shank.
The shaft, or ram, is advanced or withdrawn by rotating the tailstock handwheel located on the right end of the tailstock. The ram usually is marked in inches and/or millimeters and can be locked in place at a specific point by a locking lever.
Taper: 1. An even, gradual change in the diameter of a workpiece.
2. The process of cutting a workpiece to produce a tapered diameter.
3. A tapered section of a workpiece cut on a lathe
4. The tapered end of a tool or spindle that conforms to an industry-standard pattern such as a Morse Taper, Jacobs Taper or R8 Taper.
Through-hole: The hole that passes through the spindle. Rods that are smaller in diameter than the through-hole can extend through the hole, thus making it possible to machine the ends of a rod that otherwise would be too long for the lathe.
Tool: A cutting tool used to remove metal from a workpiece; usually made of High Speed Steel or carbide.
Tool Blank: A piece of High Speed Steel from which a cutting tool is ground on a bench grinder. Typically 5/16″ square by 2 1/2″ long for mini-lathe use.
Toolpost: A holding device mounted on the compound into which the cutting tool is clamped.
Turning: A lathe operation in which metal is removed from the outside diameter of the workpiece, thus reducing its diameter to a desired size.
Ways: Precision ground surfaces along the top of the bed on which the saddle rides. The ways are precisely aligned with the centerline of the lathe.
Work or Workpiece: Material being held in the lathe for a machining operation. Typically a rod or cylinder of metal or plastic but could also be a more complex shape such as a casting for a model airplane motor.