Bar stock
Encyclopedia
Bar stock, also colloquially known as billet, is a common form of raw purified metal
, used by industry to manufacture metal parts and products.
Most metal produced by a steel mill
or aluminium plant is formed (via rolling
or extrusion
) into long continuous strips of various size and shape. These strips are cut at regular intervals and allowed to cool, each segment becoming a piece of bar stock. A good analogy is pasta-making, in which lumps of dough are extruded into various cross-sectional shapes (from simple bar or tube shapes, such as linguine
or penne
, to more elaborate extrusions, such as rotelle
, fiori, or rotini
); cut into lengths; and then dried in that form.
A machine shop typically has a storage area containing a large variety of bar stock. To create a metal component, a bar of sufficient volume is selected from storage and brought to the machining area. This piece may then be sawed, milled
, drilled
, turned
, or ground
to remove material and create the final shape. In turning, for large-diameter work (typically more than 100 millimetres (3.9 in), although there is no universal threshold), a piece of the bar is cut off using a horizontal bandsaw to create a blank for each part. The blanks are then fed into a chucking lathe (chucker) which chucks
each one in turn. For smaller-diameter work, the entire length of bar stock is more often fed through the spindle of the lathe. The entire bar rotates with the spindle during the part-machining cycle. When the cycle ends and one part is done, the chuck opens, the bar is pulled or pushed forward ("fed") by any of various automatic means, the chuck closes, and the next cycle begins. The last step of the cycle is to cut off the machined part from the bar, which is called "parting it off" and is achieved with a "cutoff" or "part-off" tool, a tool bit
that grooves the bar all the way down to the centreline, causing the part to fall off. Then the cycle repeats.
The not-yet-cut bar protruding from the back of the spindle, rotating quickly, can present a safety hazard if it is sticking out too far and unconstrained from bending. Thus sometimes long bars must be sawn into shorter bars before being fed as "bar work" (which is the term for such work).
CNC lathes and screw machines have accessories called "bar feeders", which hold, guide, and feed the bar as commanded by the CNC control. More advanced machines may have a "bar loader" which holds multiple bars and feeds them one at a time into the bar feeder. Bar loaders are like magazines for part blanks (or pallets for milling work) in that they allow lights-out machining. The bar loader is filled with bars (or the magazine or pallet with part blanks) during working hours, and then it runs during the night unattended. Given that there is no human around to detect if something went wrong and the machine should stop, there are various kinds of sensors that are used to detect this, such as load meters, infrared beams, and, in recent years, webcam
s, which are placed inside the machine tool's enclosure and allow remote viewing of the cutting action.
Sometimes it is necessary that the bar not be very much larger than the intended part, because the metallurgical
properties of some metal alloy
s in some finishing processes may vary by how far inside the bar the metal lies. Thus an engineering drawing
will specify a certain size (or a maximum size) that the bar may start out as. These specs face the aforementioned limitation of stocking sizes versus custom mill runs; standard sizes are used wherever possible to avoid wasted expense and needless delays.
round stock with a tight tolerance diameter; it is usually ±0.0005 in (±0.013 mm). Diameters range from 0.0135 to 1.5 in (0.3429 to 38.1 mm); in the United States diameters smaller than th of an inch are made in letter drill sizes and number drill sizes, in addition to fractional sizes. Lengths are usually one or three feet (0.3 or 0.9 m). It is commonly used to make drill bit
s, taps, reamer
s, punch
es, dowel pins, and shafts. Note that the numbered sizes are different from the drill numbered sizes starting at 52. These sizes are:
Drill blanks have an undersize tolerance of +0/-0.0002 in, while reamer blanks have an oversize tolerance of -0/+0.0002 in.
Some mills also sell square stock that is held to the same tolerances under the name "drill rod".
Commonly available material grades in the U.S. are A2, D2, M2, M42, O1, S7, W1, and high speed steel
(including M2/M7).
steel that has been ground
to close tolerances (compare to drill rod). There are four types of materials available: O-1 tool steel, A-2 tool steel, A-6 tool steel, and 1018 steel (low-carbon or low-carb steel). Lengths are either 18 or long, various widths up to 16 in (406 mm) are available, and thicknesses range from 1/64 in.
Some geometrical sizes are known as .
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, used by industry to manufacture metal parts and products.
Most metal produced by a steel mill
Steel mill
A steel mill or steelworks is an industrial plant for the manufacture of steel.Steel is an alloy of iron and carbon. It is produced in a two-stage process. First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or...
or aluminium plant is formed (via rolling
Rolling (metalworking)
In metalworking, rolling is a metal forming process in which metal stock is passed through a pair of rolls. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling...
or extrusion
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
) into long continuous strips of various size and shape. These strips are cut at regular intervals and allowed to cool, each segment becoming a piece of bar stock. A good analogy is pasta-making, in which lumps of dough are extruded into various cross-sectional shapes (from simple bar or tube shapes, such as linguine
Linguine
Linguine is a form of pasta — flat like fettuccine and trenette. It is wider than spaghetti, about 1/4 to 3/8 inch, but not as wide as fettuccine. The name linguine means "little tongues" in Italian, where it is a plural of the feminine linguina. Linguine are also called trenette or bavette...
or penne
Penne
Penne is a type of pasta with cylinder-shaped pieces. Penne is the plural form of the Italian penna, deriving from Latin penna . In Italy, penne are produced in two main variants: "penne lisce" and "penne rigate" , the latter having ridges on each penna...
, to more elaborate extrusions, such as rotelle
Rotelle
Rotelle are a type of pasta resembling wheels with spokes. It is similar to Fiori.The name derives from the Italian word for little wheels...
, fiori, or rotini
Rotini
Rotini is a type of helix- or corkscrew-shaped pasta. The name derives from the Italian for twists. It is related to fusilli, but has a tighter helix, i.e. with a smaller pitch. It should not be confused with rotelle ....
); cut into lengths; and then dried in that form.
A machine shop typically has a storage area containing a large variety of bar stock. To create a metal component, a bar of sufficient volume is selected from storage and brought to the machining area. This piece may then be sawed, milled
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
, drilled
Drilling
Drilling is a cutting process that uses a drill bit to cut or enlarge a hole in solid materials. The drill bit is a multipoint, end cutting tool...
, turned
Turning
Turning is the process whereby a single point cutting tool is parallel to the surface. It can be done manually, in a traditional form of lathe, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of...
, or ground
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
to remove material and create the final shape. In turning, for large-diameter work (typically more than 100 millimetres (3.9 in), although there is no universal threshold), a piece of the bar is cut off using a horizontal bandsaw to create a blank for each part. The blanks are then fed into a chucking lathe (chucker) which chucks
Chuck (engineering)
A chuck is a specialized type of clamp used to hold an object, usually an object with radial symmetry, especially a cylindrical object. It is most commonly used to hold a rotating tool or a rotating workpiece...
each one in turn. For smaller-diameter work, the entire length of bar stock is more often fed through the spindle of the lathe. The entire bar rotates with the spindle during the part-machining cycle. When the cycle ends and one part is done, the chuck opens, the bar is pulled or pushed forward ("fed") by any of various automatic means, the chuck closes, and the next cycle begins. The last step of the cycle is to cut off the machined part from the bar, which is called "parting it off" and is achieved with a "cutoff" or "part-off" tool, a tool bit
Tool bit
The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or...
that grooves the bar all the way down to the centreline, causing the part to fall off. Then the cycle repeats.
The not-yet-cut bar protruding from the back of the spindle, rotating quickly, can present a safety hazard if it is sticking out too far and unconstrained from bending. Thus sometimes long bars must be sawn into shorter bars before being fed as "bar work" (which is the term for such work).
CNC lathes and screw machines have accessories called "bar feeders", which hold, guide, and feed the bar as commanded by the CNC control. More advanced machines may have a "bar loader" which holds multiple bars and feeds them one at a time into the bar feeder. Bar loaders are like magazines for part blanks (or pallets for milling work) in that they allow lights-out machining. The bar loader is filled with bars (or the magazine or pallet with part blanks) during working hours, and then it runs during the night unattended. Given that there is no human around to detect if something went wrong and the machine should stop, there are various kinds of sensors that are used to detect this, such as load meters, infrared beams, and, in recent years, webcam
Webcam
A webcam is a video camera that feeds its images in real time to a computer or computer network, often via USB, ethernet, or Wi-Fi.Their most popular use is the establishment of video links, permitting computers to act as videophones or videoconference stations. This common use as a video camera...
s, which are placed inside the machine tool's enclosure and allow remote viewing of the cutting action.
Standard sizes throughout a supply chain
To stock every possible size of bar stock (every possible fraction of a millimetre or inch in diameter or thickness) is impossible. Thus, bar stock is stocked by metals supply houses in various standard sizes, arrayed in discrete steps. For example, round bar with diameters of even millimetres (or in the USA, on the eighths of an inch) can usually be ordered from standing stock. Bar diameters of nonstandard sizes can also be obtained, but only as a separate mill run from the rolling mill. Thus they are much more expensive than the standard sizes, can take much longer delivery time, and are not desirable as inventory for the supply house or the machine shop (because the chance of selling or using any particular custom size is slim).Sometimes it is necessary that the bar not be very much larger than the intended part, because the metallurgical
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
properties of some metal alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s in some finishing processes may vary by how far inside the bar the metal lies. Thus an engineering drawing
Engineering drawing
An engineering drawing, a type of technical drawing, is used to fully and clearly define requirements for engineered items.Engineering drawing produces engineering drawings . More than just the drawing of pictures, it is also a language—a graphical language that communicates ideas and information...
will specify a certain size (or a maximum size) that the bar may start out as. These specs face the aforementioned limitation of stocking sizes versus custom mill runs; standard sizes are used wherever possible to avoid wasted expense and needless delays.
Drill rod
Drill rod is tool steelTool steel
Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures...
round stock with a tight tolerance diameter; it is usually ±0.0005 in (±0.013 mm). Diameters range from 0.0135 to 1.5 in (0.3429 to 38.1 mm); in the United States diameters smaller than th of an inch are made in letter drill sizes and number drill sizes, in addition to fractional sizes. Lengths are usually one or three feet (0.3 or 0.9 m). It is commonly used to make drill bit
Drill bit
Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....
s, taps, reamer
Reamer
A reamer is a metalworking tool used to create an accurate sized hole. The process is called reaming. They may be used as a hand tool or in a machine tool, such as a milling machine or drill press.-Construction:...
s, punch
Punch (tool)
A punch is a hard metal rod with a shaped tip at one end and a blunt butt end at the other, which is usually struck by a hammer. Punches are used to drive objects, such as nails, or to form an impression of the tip on a workpiece...
es, dowel pins, and shafts. Note that the numbered sizes are different from the drill numbered sizes starting at 52. These sizes are:
|
|
Drill blanks have an undersize tolerance of +0/-0.0002 in, while reamer blanks have an oversize tolerance of -0/+0.0002 in.
Some mills also sell square stock that is held to the same tolerances under the name "drill rod".
Commonly available material grades in the U.S. are A2, D2, M2, M42, O1, S7, W1, and high speed steel
High speed steel
High speed steelMost copyeditors today would tend to choose to style the unit adjective high-speed with a hyphen, rendering the full term as high-speed steel, and this styling is not uncommon . However, it is true that in the metalworking industries the styling high speed steel is long-established...
(including M2/M7).
Ground flat stock
Ground flat stock is annealedAnnealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
steel that has been ground
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
to close tolerances (compare to drill rod). There are four types of materials available: O-1 tool steel, A-2 tool steel, A-6 tool steel, and 1018 steel (low-carbon or low-carb steel). Lengths are either 18 or long, various widths up to 16 in (406 mm) are available, and thicknesses range from 1/64 in.
Some geometrical sizes are known as .