![Drill bits 2017 G1](https://upload.wikimedia.org/wikipedia/commons/d/d9/Drill_bits_2017_G1.jpg)
Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order to create holes drill bits are usually attached to a
drill
A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to ...
, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the ''shank'' in the
chuck
Chuck is a masculine given name or a nickname for Charles or Charlie. It may refer to:
People
Arts and entertainment
* Chuck Alaimo, American saxophonist, leader of the Chuck Alaimo Quartet
* Chuck Barris (1929–2017), American TV producer
* C ...
.
Drills come in standardized
drill bit sizes Drill bits are the cutting tools of drilling machines. They can be made in any size to order, but standards organizations have defined sets of sizes that are produced routinely by drill bit manufacturers and stocked by distributors.
In the U.S., fr ...
. A comprehensive
drill bit and tap size chart lists
metric
Metric or metrical may refer to:
* Metric system, an internationally adopted decimal system of measurement
* An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement
Mathematics
In mathema ...
and
imperial
Imperial is that which relates to an empire, emperor, or imperialism.
Imperial or The Imperial may also refer to:
Places
United States
* Imperial, California
* Imperial, Missouri
* Imperial, Nebraska
* Imperial, Pennsylvania
* Imperial, Texa ...
sized drills alongside the required screw tap sizes. There are also certain specialized drill bits that can create holes with a non-circular cross-section.
Characteristics
Drill geometry has several characteristics:
*The spiral (or rate of twist) in the drill bit controls the rate of
chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genomi ...
removal. A fast spiral (high twist rate or "compact flute") drill bit is used in high feed rate applications under low spindle speeds, where removal of a large volume of chips is required. Low spiral (low twist rate or "elongated flute") drill bits are used in cutting applications where high cutting speeds are traditionally used, and where the material has a tendency to
gall
Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
on the bit or otherwise clog the hole, such as
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
or
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
.
*The point angle, or the angle formed at the tip of the bit, is determined by the material the bit will be operating in. Harder materials require a larger point angle, and softer materials require a sharper angle. The correct point angle for the hardness of the material influences wandering, chatter, hole shape, and wear rate.
*The lip angle determines the amount of support provided to the cutting edge. A greater lip angle will cause the bit to cut more aggressively under the same amount of point pressure as a bit with a smaller lip angle. Both conditions can cause binding, wear, and eventual catastrophic failure of the tool. The proper amount of lip clearance is determined by the point angle. A very acute point angle has more web surface area presented to the work at any one time, requiring an aggressive lip angle, where a flat bit is extremely sensitive to small changes in lip angle due to the small surface area supporting the cutting edges.
*The functional length of a bit determines how deep a hole can be drilled, and also determines the stiffness of the bit and accuracy of the resultant hole. While longer bits can drill deeper holes, they are more flexible meaning that the holes they drill may have an inaccurate location or wander from the intended axis. Twist drill bits are available in standard lengths, referred to as Stub-length or Screw-Machine-length (short), the extremely common
Jobber-length (medium), and Taper-length or Long-Series (long).
Most drill bits for consumer use have straight shanks. For heavy duty drilling in industry, bits with
tapered shanks are sometimes used. Other types of shank used include hex-shaped, and various proprietary quick release systems.
The diameter-to-length ratio of the drill bit is usually between 1:1 and 1:10. Much higher ratios are possible (e.g., "aircraft-length" twist bits, pressured-oil
gun drill bits, etc.), but the higher the ratio, the greater the technical challenge of producing good work.
The best geometry to use depends upon the properties of the material being drilled. The following table lists geometries recommended for some commonly drilled materials.
Materials
Many different materials are used for or on drill bits, depending on the required application. Many hard materials, such as carbides, are much more brittle than steel, and are far more subject to breaking, particularly if the drill is not held at a very constant angle to the workpiece; e.g., when hand-held.
Steels
*Soft low-carbon
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
bits are inexpensive, but do not hold an edge well and require frequent sharpening. They are used only for drilling wood; even working with
hardwood
Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood (which comes from ...
s rather than
softwood
file:Pinus sylvestris wood ray section 1 beentree.jpg, Scots Pine, a typical and well-known softwood
Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The main diff ...
s can noticeably shorten their lifespan.
*Bits made from high-carbon steel are more durable than low-carbon steel bits due to the properties conferred by
hardening and tempering the material. If they are overheated (e.g., by frictional heating while drilling) they lose their
temper
Temper, tempered or tempering may refer to:
Heat treatment
* Tempering (metallurgy), a heat treatment technique to increase the toughness of iron-based alloys
** Temper mill, a steel processing line
* Tempering (spices), a cooking technique where ...
, resulting in a soft cutting edge. These bits can be used on wood or metal.
*
High-speed steel
High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material.
It is often used in power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s in that ...
(HSS) is a form of
tool steel
Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive har ...
; HSS bits are hard and much more resistant to heat than high-carbon steel. They can be used to drill metal, hardwood, and most other materials at greater cutting speeds than carbon-steel bits, and have largely replaced carbon steels.
*
Cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...
steel
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
s are variations on high-speed steel that contain more cobalt. They hold their hardness at much higher temperatures and are used to drill
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
and other hard materials. The main disadvantage of cobalt steels is that they are more brittle than standard HSS.
Others
*
Tungsten carbide
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...
and other
carbide
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Interstitial / Metallic carbides
The carbides of the ...
s are extremely hard and can drill virtually all materials, while holding an edge longer than other bits. The material is expensive and much more brittle than steels; consequently they are mainly used for drill-bit tips, small pieces of hard material fixed or
brazed
Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Brazing differs from we ...
onto the tip of a bit made of less hard metal. However, it is becoming common in job shops to use solid carbide bits. In very small sizes it is difficult to fit carbide tips; in some industries, most notably
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
manufacturing, requiring many holes with diameters less than 1 mm, solid carbide bits are used.
*Polycrystalline diamond (PCD) is among the hardest of all tool materials and is therefore extremely resistant to wear. It consists of a layer of diamond particles, typically about thick, bonded as a
sintered
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
mass to a tungsten-carbide support. Bits are fabricated using this material by either brazing small segments to the tip of the tool to form the cutting edges or by sintering PCD into a vein in the tungsten-carbide "nib". The nib can later be brazed to a carbide shaft; it can then be ground to complex geometries that would otherwise cause braze failure in the smaller "segments". PCD bits are typically used in the automotive, aerospace, and other industries to drill abrasive aluminum alloys, carbon-fiber reinforced plastics, and other abrasive materials, and in applications where machine downtime to replace or sharpen worn bits is exceptionally costly. PCD is not used on ferrous metals due to excess wear resulting from a reaction between the carbon in the PCD and the iron in the metal.
Coatings
*
Black oxide
Black oxide or blackening is a conversion coating for ferrous materials, stainless steel, copper and copper based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance, for appearance, and to minimize light ...
is an inexpensive black coating. A black oxide coating provides heat resistance and lubricity, as well as corrosion resistance. The coating increases the life of high-speed steel bits.
*
Titanium nitride
Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface prope ...
(TiN) is a very hard metallic material that can be used to coat a high-speed steel bit (usually a twist bit), extending the cutting life by three or more times. Even after sharpening, the leading edge of coating still provides improved cutting and lifetime.
*
Titanium aluminum nitride
Titanium aluminium nitride (TiAlN) or aluminium titanium nitride (AlTiN; for aluminium contents higher than 50%) is a group of metastable hard coatings consisting of nitrogen and the metallic elements aluminium and titanium. Four important composi ...
(TiAlN) is a similar coating that can extend tool life five or more times.
*Titanium carbon nitride (TiCN) is another coating also superior to TiN.
*Diamond powder is used as an abrasive, most often for cutting tile, stone, and other very hard materials. Large amounts of heat are generated by friction, and diamond-coated bits often have to be water-cooled to prevent damage to the bit or the workpiece.
*
Zirconium nitride
Zirconium nitride () is an inorganic compound used in a variety of ways due to its properties.
Properties
ZrN grown by physical vapor deposition (PVD) is a light gold color similar to elemental gold. ZrN has a room-temperature electrical resist ...
has been used as a drill-bit coating for some tools under the
Craftsman brand name.
*Al-Chrome Silicon Nitride (AlCrSi/Ti)N is a multilayer coating made of alternating nanolayer, developed using
chemical vapor deposition
Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
In typical CVD, the wafer (substra ...
technique, is used in drilling
carbon fiber reinforced polymer
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
(CFRP) and CFRP-Ti stack. (AlCrSi/Ti)N is a superhard ceramic coating, which performs better than other coated and uncoated drill.
[. Swan et al (September 7, 2018). "Tool Wear of Advanced Coated Tools in Drilling of CFRP." ASME. J. Manuf. Sci. Eng. November 2018; 140(11): 111018. https://doi.org/10.1115/1.4040916]
*BAM coating is
Boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
-Aluminum-
Magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
BAlMgB14 is a superhard ceramic coating also used in composite drilling.
Universal bits
General-purpose drill bits can be used in wood, metal, plastic, and most other materials.
Twist drill bit
The twist drill bit is the type produced in largest quantity today. It comprises a cutting point at the tip of a cylindrical shaft with helical flutes; the flutes act as an
Archimedean screw
The Archimedes screw, also known as the Archimedean screw, hydrodynamic screw, water screw or Egyptian screw, is one of the earliest hydraulic machines. Using Archimedes screws as water pumps (Archimedes screw pump (ASP) or screw pump) dates back ...
and lift
swarf
Swarf, also known as chips or by other process-specific names (such as turnings, filings, or shavings), are pieces of metal, wood, or plastic that are the debris or waste resulting from machining, woodworking, or similar subtractive (material-r ...
out of the hole.
The modern-style twist drill bit was invented by Sir Joseph Whitworth in 1860. They were later improved by Steven A. Morse of
East Bridgewater, Massachusetts
East Bridgewater is a town in Plymouth County, Massachusetts, United States. The population was 14,440 at the 2020 census. It is also a part of Massachusetts' 8th congressional district, of which it is represented by Stephen Lynch.
History
The ...
, who experimented with the pitch of the twist. The original method of manufacture was to cut two grooves in opposite sides of a round bar, then to twist the bar (giving the tool its name) to produce the helical flutes. Nowadays, the drill bit is usually made by rotating the bar while moving it past a
grinding
Grind is the cross-sectional shape of a blade.
Grind, grinds, or grinding may also refer to:
Grinding action
* Grinding (abrasive cutting), a method of crafting
* Grinding (dance), suggestive club dancing
* Grinding (video gaming), repetitive and ...
wheel to cut the
flutes
The flute is a family of classical music instrument in the woodwind group. Like all woodwinds, flutes are aerophones, meaning they make sound by vibrating a column of air. However, unlike woodwind instruments with reeds, a flute is a reedless ...
in the same manner as
cutting helical gears.
Twist drill bits range in diameter from and can be as long as .
The geometry and sharpening of the cutting edges is crucial to the performance of the bit. Small bits that become blunt are often discarded because sharpening them correctly is difficult and they are cheap to replace. For larger bits, special grinding jigs are available. A special
tool grinder
A Tool and Cutter Grinder is used to sharpen milling cutters and tool bits along with a host of other cutting tools.
It is an extremely versatile machine used to perform a variety of grinding operations: surface, cylindrical, or complex shapes ...
is available for sharpening or reshaping cutting surfaces on twist drill bits in order to optimize the bit for a particular material.
Manufacturers can produce special versions of the twist drill bit, varying the geometry and the materials used, to suit particular machinery and particular materials to be cut. Twist drill bits are available in the widest choice of tooling materials. However, even for industrial users, most holes are drilled with standard
high-speed steel
High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material.
It is often used in power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s in that ...
bits.
The most common twist drill bit (sold in general hardware stores) has a point angle of 118 degrees, acceptable for use in wood, metal, plastic, and most other materials, although it does not perform as well as using the optimum angle for each material. In most materials it does not tend to wander or dig in.
A more aggressive angle, such as 90 degrees, is suited for very soft plastics and other materials; it would wear rapidly in hard materials. Such a bit is generally self-starting and can cut very quickly. A shallower angle, such as 150 degrees, is suited for drilling steels and other tougher materials. This style of bit requires a starter hole, but does not bind or suffer premature wear so long as a suitable feed rate is used.
Drill bits with no point angle are used in situations where a blind, flat-bottomed hole is required. These bits are very sensitive to changes in lip angle, and even a slight change can result in an inappropriately fast cutting drill bit that will suffer premature wear.
''Long series'' drill bits are unusually long twist drill bits. However, they are not the best tool for routinely drilling deep holes, as they require frequent withdrawal to clear the flutes of swarf and to prevent breakage of the bit. Instead,
gun drill
Gun drills (through coolant drill) are straight fluted drills which allow cutting fluid (either compressed air or a suitable liquid) to be injected through the drill's hollow body to the cutting face. They are used for deep hole drilling—a ...
(through coolant drill) bits are preferred for deep hole drilling.
Image:drill twist 1.jpg, Twist drill bit cutting edges
Image:drill twist morse.jpg, Twist drill bit with Morse taper
Morse may refer to:
People
* Morse (surname)
* Morse Goodman (1917-1993), Anglican Bishop of Calgary, Canada
* Morse Robb (1902–1992), Canadian inventor and entrepreneur
Geography Antarctica
* Cape Morse, Wilkes Land
* Mount Morse, Church ...
shank
Image:LongSeriesDrill-11 32.jpg, drill bits - long-series morse, plain morse, jobber
Step drill bit
A step drill bit is a drill bit that has the tip ground down to a different diameter. The transition between this ground diameter and the original diameter is either straight, to form a counterbore, or angled, to form a countersink. The advantage to this style is that both diameters have the same flute characteristics, which keeps the bit from clogging when drilling in softer materials, such as aluminum; in contrast, a drill bit with a slip-on collar does not have the same benefit. Most of these bits are custom-made for each application, which makes them more expensive.
Unibit
A unibit (often called a
step drill bit) is a roughly
conical
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines conn ...
bit with a
stairs
Stairs are a structure designed to bridge a large vertical distance between lower and higher levels by dividing it into smaller vertical distances. This is achieved as a diagonal series of horizontal platforms called steps which enable passage ...
tep profile.
Due to its design, a single bit can be used for drilling a wide range of hole sizes. Some bits come to a point and are thus self-starting. The larger-size bits have blunt tips and are used for hole enlarging.
Unibits are commonly used on sheet metal
and in general construction. One drill bit can drill the entire range of holes necessary on a countertop, speeding up installation of fixtures. They are often used on softer materials, such as plywood, particle board, drywall, acrylic, and laminate. They can be used on very thin sheet metal, but metals tend to cause premature bit wear and dulling.
Unibits are ideal for use in electrical work where thin steel, aluminum or plastic boxes and chassis are encountered. The short length of the unibit and ability to vary the diameter of the finished hole is an advantage in chassis or front panel work. The finished hole can often be made quite smooth and burr-free, especially in plastic.
An additional use of unibits is deburring holes left by other bits, as the sharp increase to the next step size allows the cutting edge to scrape burrs off the entry surface of the workpiece. However, the straight flute is poor at chip ejection, and can cause a burr to be formed on the exit side of the hole, more so than a spiral twist drill bit turning at high speed.
The unibit was invented by Harry C. Oakes and
patent
A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
ed in 1973. It was sold only by the Unibit Corporation in the 1980s until the patent expired, and was later sold by other companies. Unibit is a trademark of
Irwin Industrial Tools
Irwin Industrial Tools is an American manufacturer and distributor of hand tools and power tool accessories. It is owned by Stanley Black & Decker. It is best known for producing Vise-Grip locking pliers. Additionally, it produces clamps, drill ...
.
Although it is claimed that the stepped drill was invented by Harry C. Oakes it was in fact first produced by Bradley Engineering, Wandsworth, London in the 1960s and named the Bradrad. It was marketed under this name until the patent was sold to Halls Ltd.uk by whom it is still produced.
Hole saw
Hole saws take the form of a short open cylinder with saw-teeth on the open edge, used for making relatively large holes in thin material. They remove material only from the edge of the hole, cutting out an intact disc of material, unlike many drills which remove all material in the interior of the hole. They can be used to make large holes in wood, sheet metal and other materials.
Metal drill bits
Center and spotting drill bit
Center drill bits, occasionally known as Slocombe drill bits, are used in
metalworking
Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale ...
to provide a starting hole for a larger-sized drill bit or to make a conical indentation in the end of a workpiece in which to mount a
lathe center
A lathe center, often shortened to center, is a tool that has been ground to a point to accurately position a workpiece on an axis. They usually have an included angle of 60°, but in heavy machining situations an angle of 75° is used.
The prim ...
. In either use, the name seems appropriate, as the bit is either establishing the ''center'' of a hole or making a conical hole for a lathe ''center''. However, the true purpose of a center drill bit is the latter task, while the former task is best done with a ''spotting drill bit'' (as explained in detail below). Nevertheless, because of the frequent lumping together of both the terminology and the tool use, suppliers may call center drill bits ''combined-drill-and-countersinks'' in order to make it unambiguously clear what product is being ordered. They are numbered from 00 to 10 (smallest to largest).
Use in making holes for lathe centers
Center drill bits are meant to create a conical hole for "between centers" manufacturing processes (typically lathe or cylindrical-grinder work). That is, they provide a location for a (live, dead, or driven) center to locate the part about an axis. A workpiece machined between centers can be safely removed from one process (perhaps turning in a lathe) and set up in a later process (perhaps a
grinding
Grind is the cross-sectional shape of a blade.
Grind, grinds, or grinding may also refer to:
Grinding action
* Grinding (abrasive cutting), a method of crafting
* Grinding (dance), suggestive club dancing
* Grinding (video gaming), repetitive and ...
operation) with a negligible loss in the co-axiality of features (usually
total indicator reading In metrology and the fields that it serves (such as manufacturing, machining, and engineering), total indicator reading (TIR), also known by the newer name full indicator movement (FIM), is the difference between the maximum and minimum measurements ...
(TIR) less than ; and TIR < is held in cylindrical grinding operations, as long as conditions are correct).
Use in spotting hole centers
Traditional twist drill bits may tend to wander when started on an unprepared surface. Once a bit wanders off course it is difficult to bring it back on center. A center drill bit frequently provides a reasonable starting point as it is short and therefore has a reduced tendency to wander when drilling is started.
While the above is a common use of center drill bits, it is a technically incorrect practice and should not be considered for production use. The correct tool to start a traditionally drilled hole (a hole drilled by a high-speed steel (HSS) twist drill bit) is a ''spotting drill bit'' (or a ''spot drill bit'', as they are referenced in the U.S.). The included angle of the spotting drill bit should be the same as, or greater than, the conventional drill bit so that the drill bit will then start without undue stress on the bit's corners, which would cause premature failure of the bit and a loss of hole quality.
Most modern solid-carbide bits should not be used in conjunction with a spot drill bit or a center drill bit, as solid-carbide bits are specifically designed to start their own hole. Usually, spot drilling will cause premature failure of the solid-carbide bit and a certain loss of hole quality. If it is deemed necessary to
chamfer
A chamfer or is a transitional edge between two faces of an object. Sometimes defined as a form of bevel, it is often created at a 45° angle between two adjoining right-angled faces.
Chamfers are frequently used in machining, carpentry, fu ...
a hole with a spot or center drill bit when a solid-carbide drill bit is used, it is best practice to do so after the hole is drilled.
When drilling with a hand-held drill the flexibility of the bit is not the primary source of inaccuracy—it is the user's hands. Therefore, for such operations, a
center punch
A punch is a tool used to indent or create a hole through a hard surface. They usually consist of a hard metal rod with a narrow tip at one end and a broad flat "butt" at the other. When used, the narrower end is pointed against a target surf ...
is often used to spot the hole center prior to drilling a
pilot hole
In construction, a pilot hole is a small hole drilled into a piece of construction material. Its purpose may be:
#to guide a larger drill to the appropriate location and ease the job of the larger drill
#allow for the insertion of another hole-m ...
.
Core drill bit
![Magnetic Drilling Machine from BDS](https://upload.wikimedia.org/wikipedia/commons/0/00/Magnetic_Drilling_Machine_from_BDS.jpg)
The term core drill bit is used for two quite different tools.
Enlarging holes
A bit used to enlarge an existing hole is called a core drill bit. The existing hole may be the result of a
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the central ...
from a
casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
or a stamped (punched) hole. The name comes from its first use, for drilling out the hole left by a ''foundry core'', a cylinder placed in a mould for a casting that leaves an irregular hole in the product. This core drill bit is solid.
These core drill bits are similar in appearance to
reamer
A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precisio ...
s as they have no cutting point or means of starting a hole. They have 3 or 4 flutes which enhances the finish of the hole and ensures the bit cuts evenly. Core drill bits differ from reamers in the amount of material they are intended to remove. A reamer is only intended to enlarge a hole a slight amount which, depending on the reamers size, may be anything from 0.1 millimeter to perhaps a millimeter. A core drill bit may be used to double the size of a hole.
Using an ordinary two-flute twist drill bit to enlarge the hole resulting from a casting core will not produce a clean result, the result will possibly be out of round, off center and generally of poor finish. The two fluted drill bit also has a tendency to grab on any protuberance (such as
flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid ...
) which may occur in the product.
Extracting core
A hollow cylindrical bit which will cut a hole with an
annular
Annulus (or anulus) or annular indicates a ring- or donut-shaped area or structure. It may refer to:
Human anatomy
* ''Anulus fibrosus disci intervertebralis'', spinal structure
* Annulus of Zinn, a.k.a. annular tendon or ''anulus tendineus com ...
cross-section and leave the inner cylinder of material (the "core") intact, often removing it, is also called a core drill bit or
annular cutter
An annular cutter (also called as core drill, core cutter, broach cutter, trepanning drill, hole saw, or cup-type cutter) is form of core drill used to create holes in metal. An annular cutter, named after the annulus shape, cuts only a groove ...
. Unlike other drills, the purpose is often to retrieve the core rather than simply to make a hole. A diamond core drill bit is intended to cut an annular hole in the workpiece. Large bits of similar shape are used for geological work, where a deep hole is drilled in sediment or ice and the drill bit, which now contains an intact core of the material drilled with a diameter of several centimeters, is retrieved to allow study of the
strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
.
Countersink bit
A countersink is a conical hole cut into a manufactured object; a countersink bit (sometimes called simply countersink) is the cutter used to cut such a hole. A common use is to allow the head of a bolt or screw, with a shape exactly matching the countersunk hole, to sit flush with or below the surface of the surrounding material. (By comparison, a counterbore makes a flat-bottomed hole that might be used with a hex-headed capscrew.) A countersink may also be used to remove the burr left from a drilling or tapping operation.
Ejector drill bit
Used almost exclusively for deep hole drilling of medium to large diameter holes (approximately diameter). An ejector drill bit uses a specially designed carbide cutter at the point. The bit body is essentially a tube within a tube. Flushing water travels down between the two tubes. Chip removal is back through the center of the bit.
Gun drill bit
Gun drills are straight fluted drills which allow
cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...
(either compressed air or a suitable liquid) to be injected through the drill's hollow body to the cutting face.
Indexable drill bit
Indexable drill bits are primarily used in
CNC
Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a ...
and other high precision or production equipment, and are the most expensive type of drill bit, costing the most per diameter and length. Like
indexable lathe tools and
milling cutter
Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations (and occasionally in other machine tools). They remove material by their movement within the machine (e.g., a ball nose mill) ...
s, they use replaceable carbide or ceramic inserts as a cutting face to alleviate the need for a tool grinder. One insert is responsible for the outer radius of the cut, and another insert is responsible for the inner radius. The tool itself handles the point deformity, as it is a low-wear task. The bit is hardened and coated against wear far more than the average drill bit, as the shank is non-consumable. Almost all indexable drill bits have multiple coolant channels for prolonged tool life under heavy usage. They are also readily available in odd configurations, such as straight flute, fast spiral, multiflute, and a variety of cutting face geometries.
Typically indexable drill bits are used in holes that are no deeper than about 5 times the bit diameter. They are capable of quite high axial loads and cut very fast.
Left-hand bit
Left-hand bits are almost always twist bits and are predominantly used in the
repetition
Repetition may refer to:
* Repetition (rhetorical device), repeating a word within a short space of words
*Repetition (bodybuilding), a single cycle of lifting and lowering a weight in strength training
*Working title for the 1985 slasher film '' ...
engineering industry on screw machines or drilling heads. Left-handed drill bits allow a machining operation to continue where either the spindle cannot be reversed or the design of the machine makes it more efficient to run left-handed. With the increased use of the more versatile CNC machines, their use is less common than when specialized machines were required for machining tasks.
Screw extractor
A screw extractor held in a tap wrench
A screw extractor is a tool for removing broken or seized screws. There are two types: one has a spiral flute structure, commonly called an easy out after the trademarked name ''EZ-Out''; the other has a str ...
s are essentially left-hand bits of specialized shape, used to remove common right-hand
screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
s whose heads are broken or too damaged to allow a screwdriver tip to engage, making use of a screwdriver impossible. The extractor is pressed against the damaged head and rotated counter-clockwise and will tend to jam in the damaged head and then turn the screw counter-clockwise, unscrewing it. For screws that break off deeper in the hole, an extractor set will often include left handed drill bits of the appropriate diameters so that grab holes can be drilled into the screws in a left handed direction, preventing further tightening of the broken piece.
Metal spade bit
A spade drill bit for metal is a two part bit with a tool holder and an insertable tip, called an insert. The inserts come in various sizes that range from . The tool holder usually has a coolant passage running through it.
[McMaster-Carr, p. 2438, 116th edition.] They are capable of cutting to a depth of about 10 times the bit diameter. This type of drill bit can also be used to make stepped holes.
Straight fluted bit
Straight fluted drill bits do not have a helical twist like twist drill bits do. They are used when drilling
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
or
brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other with ...
because they have less of a tendency to "dig in" or grab the material.
Trepan
A trepan, sometimes called a BTA drill bit (after the Boring and Trepanning Association), is a drill bit that cuts an annulus and leaves a center core. Trepans usually have multiple carbide inserts and rely on water to cool the cutting tips and to flush chips out of the hole. Trepans are often used to cut large diameters and deep holes. Typical bit diameters are and hole depth from up to .
Wood drill bits
Brad point bit
The brad point drill bit (also known as lip and spur drill bit, and dowel drill bit) is a variation of the
twist drill bit which is optimized for drilling in wood.
Conventional twist drill bits tend to wander when presented to a flat workpiece. For metalwork, this is countered by drilling a pilot hole with a spotting drill bit. In wood, the brad point drill bit is another solution: the center of the drill bit is given not the straight chisel of the twist drill bit, but a spur with a sharp point, and four sharp corners to cut the wood. While drilling, the sharp point of the spur pushes into the soft wood to keep the drill bit in line.
Metals are typically
isotropic
Isotropy is uniformity in all orientations; it is derived . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe ...
, so even an ordinary twist drill bit will shear the edges of the hole cleanly. ''Wood'' drilled across the grain, however, produces long strands of wood fiber. These long strands tend to pull out of the hole, rather than being cleanly cut at the hole edge. The brad point drill bit has the outside corner of the cutting edges leading, so that it cuts the periphery of the hole before the inner parts of the cutting edges plane off the base of the hole. By cutting the periphery first, the lip maximizes the chance that the fibers can be cut cleanly, rather than having to be pulled messily from the timber.
Brad point drill bits are also effective in soft plastic. When using conventional twist drill bits in a handheld drill, where the drilling direction is not maintained perfectly throughout the operation, there is a tendency for hole edges to be "smeared" due to side friction and heat.
In metal, the brad point drill bit is confined to drilling only the thinnest and softest
sheet metal
Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes.
Thicknesses can vary significantly; ex ...
s, ideally with a
drill press
A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to i ...
. The bits have an extremely fast cutting tool geometry: no point angle, combined with a large (considering the flat cutting edge) lip angle, causes the edges to take a very aggressive cut with relatively little point pressure. This means these bits tend to bind in metal; given a workpiece of sufficient thinness, they have a tendency to punch through and leave the bit's cross-sectional geometry behind.
Brad point drill bits are ordinarily available in diameters from .
Wood spade bit
Spade bits are used for rough boring in wood. They tend to cause splintering when they emerge from the workpiece. Woodworkers avoid splintering by finishing the hole from the opposite side of the work. Spade bits are flat, with a centering point and two cutters. The cutters are often equipped with spurs in an attempt to ensure a cleaner hole. With their small shank diameters relative to their boring diameters, spade bit shanks often have flats forged or ground into them to prevent slipping in drill chucks. Some bits are equipped with long shanks and have a small hole drilled through the flat part, allowing them to be used much like a
bell-hanger bit. Intended for high speed use, they are used with electric hand drills. Spade bits are also sometimes referred to as "paddle bits".
Spade drill bits are ordinarily available in diameters from 6 to 36 mm, or to inches.
Image:Spade bits.JPG, Spade bits
Image:drill spade tiny.jpg, Tiny spade bit
Spoon bit
Spoon bits consist of a grooved shank with a point shaped somewhat like the bowl of a spoon, with the cutting edge on the end. The more common type is like a gouge bit that ends in a slight point. This is helpful for starting the hole, as it has a center that will not wander or walk. These bits are used by chair-makers for boring or reaming holes in the seats and arms of chairs. Their design is ancient, going back to Roman times. Spoon bits have even been found in Viking excavations. Modern spoon bits are made of hand-forged carbon steel, carefully heat-treated and then hand ground to a fine edge.
Spoon bits are the traditional boring tools used with a brace. They should never be used with a power drill of any kind. Their key advantage over regular brace bits and power drill bits is that the angle of the hole can be adjusted. This is very important in chairmaking, because all the angles are usually eyeballed. Another advantage is that they do not have a lead screw, so they can be drilled successfully in a chair leg without having the lead screw peek out the other side.
When reaming a pre-bored straight-sided hole, the spoon bit is inserted into the hole and rotated in a clockwise direction with a carpenters' brace until the desired taper is achieved. When boring into solid wood, the bit should be started in the vertical position; after a "dish" has been created and the bit has begun to "bite" into the wood, the angle of boring can be changed by tilting the brace a bit out of the vertical. Holes can be drilled precisely, cleanly and quickly in any wood, at any angle of incidence, with total control of direction and the ability to change that direction at will.
Parallel spoon bits are used primarily for boring holes in the seat of a
Windsor chair
A Windsor chair is a chair built with a solid wooden seat into which the chair-back and legs are round- tenoned, or pushed into drilled holes, in contrast to standard chairs (whose back legs and back uprights are continuous). The seats of Windsor ...
to take the back spindles, or similar round-tenon work when assembling furniture frames in
green woodworking
Green woodworking is a form of wood craft or in broad terms, carpentry
Carpentry is a skilled trade and a craft in which the primary work performed is the cutting, shaping and installation of building materials during the construction o ...
work.
The spoon bit may be honed by using a slipstone on the inside of the cutting edge; the outside edge should never be touched.
Forstner bit
Forstner bits, named after their inventor,
Benjamin Forstner, bore precise, flat-bottomed holes in wood, in any orientation with respect to the wood grain. They can cut on the edge of a block of wood, and can cut overlapping holes; for such applications they are normally used in drill presses or lathes rather than in hand-held electric drills. Because of the flat bottom of the hole, they are useful for drilling through veneer already glued to add an inlay.
The bit includes a center
brad point which guides it throughout the cut (and incidentally spoils the otherwise flat bottom of the hole). The cylindrical cutter around the perimeter shears the wood fibers at the edge of the bore, and also helps guide the bit into the material more precisely. Forstner bits have radial cutting edges to plane off the material at the bottom of the hole. The bits shown in the images have two radial edges; other designs may have more. Forstner bits have no mechanism to clear chips from the hole, and therefore must be pulled out periodically.
Sawtooth bits are also available, which include many more cutting edges to the cylinder. These cut faster, but produce a more ragged hole. They have advantages over Forstner bits when boring into
end grain
Wood grain is the longitudinal arrangement of wood fibers or the pattern resulting from such an arrangement.
Definition and meanings
R. Bruce Hoadley wrote that ''grain'' is a "confusingly versatile term" with numerous different uses, including ...
.
Bits are commonly available in sizes from diameter. Sawtooth bits are available up to diameter.
Originally the Forstner bit was very successful with gunsmiths because of its ability to drill an exceedingly smooth-sided hole.
Center bit
The center bit is optimized for drilling in wood with a
hand brace. Many different designs have been produced.
The center of the bit is a tapered screw thread. This screws into the wood as the bit is turned, and pulls the bit into the wood. There is no need for any force to push the bit into the workpiece, only the torque to turn the bit. This is ideal for a bit for a hand tool. The radial cutting edges remove a slice of wood of thickness equal to the pitch of the central screw for each rotation of the bit. To pull the bit from the hole, either the female thread in the wood workpiece must be stripped, or the rotation of the bit must be reversed.
The edge of the bit has a sharpened spur to cut the fibers of the wood, as in the brad point drill bit. A radial cutting edge planes the wood from the base of the hole. In this version, there is minimal or no spiral to remove chips from the hole. The bit must be periodically withdrawn to clear the chips.
Some versions have two spurs. Some have two radial cutting edges.
Center bits do not cut well in the end grain of wood. The central screw tends to pull out, or to split the wood along the grain, and the radial edges have trouble cutting through the long wood fibers.
Center bits are made of relatively soft steel, and can be sharpened with a file.
Image:drill brace.jpg, A 19 mm (3/4 inch) center bit, made sometime before 1950
Image:drill tip brace.jpg, Center bit tip detail
Auger bit
The cutting principles of the auger bit are the same as those of the center bit above. The auger adds a long deep spiral flute for effective chip removal.
Two styles of auger bit are commonly used in hand braces: the Jennings or Jennings-pattern bit has a self-feeding screw tip, two spurs and two radial cutting edges. This bit has a double flute starting from the cutting edges, and extending several inches up the shank of the bit, for waste removal. This pattern of bit was developed by Russell Jennings in the mid-19th century.
The Irwin or solid-center auger bit is similar, the only difference being that one of the cutting edges has only a "vestigal flute" supporting it, which extends only about up the shank before ending. The other flute continues full-length up the shank for waste removal. The Irwin bit may afford greater space for waste removal, greater strength (because the design allows for a center shank of increased size within the flutes, as compared to the Jenning bits), or smaller manufacturing costs. This style of bit was invented in 1884, and the rights sold to Charles Irwin who patented and marketed this pattern the following year.
Both styles of auger bits were manufactured by several companies throughout the early- and mid-20th century, and are still available new from select sources today.
The diameter of auger bits for hand braces is commonly expressed by a single number, indicating the size in 16ths of an inch. For example, #4 is 4/16 or 1/4 in (6 mm), #6 is 6/16 or 3/8 in (9 mm), #9 is 9/16 in (14 mm), and #16 is 16/16 or 1 in (25 mm). Sets commonly consist of #4-16 or #4-10 bits.
The bit shown in the picture is a modern design for use in portable power tools, made in the UK in about 1995. It has a single spur, a single radial cutting edge and a single flute. Similar auger bits are made with diameters from 6 mm (3/16 in) to 30 mm (1 3/16 in). Augers up to long are available, where the chip-clearing capability is especially valuable for drilling deep holes.
Image:drill auger.jpg, auger bit for wood
Image:drill tip auger.jpg, Auger bit tip detail
Gimlet bit
The gimlet bit is a very old design. The bit is the same style as that used in the
gimlet, a self-contained tool for boring small holes in wood by hand. Since about 1850, gimlets have had a variety of cutter designs, but some are still produced with the original version. The gimlet bit is intended to be used in a hand brace for drilling into wood. It is the usual style of bit for use in a brace for holes below about diameter.
The tip of the gimlet bit acts as a tapered screw, to draw the bit into the wood and to begin forcing aside the wood fibers, without necessarily cutting them. The cutting action occurs at the side of the broadest part of the cutter. Most drill bits cut the base of the hole. The gimlet bit cuts the side of the hole.
Image:drill gimlet.jpg, Gimlet bit for wood, made sometime before 1950.
Image:drill tip gimlet.jpg, Gimlet bit tip detail
Hinge sinker bit
The hinge sinker bit is an example of a custom drill bit design for a specific application. Many European kitchen cabinets are made from
particle board
Particle board, also known as chipboard or low-density fiberboard, is an engineered wood product manufactured from wood chips and a synthetic resin or other suitable binder, which is pressed and extruded. Particle board is often confused with ori ...
or
medium-density fiberboard
Medium-density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibres, often in a defibrator, combining it with wax and a resin binder, and forming it into panels by applying high temp ...
(MDF) with a laminated
melamine resin
Melamine resin or melamine formaldehyde (also shortened to melamine) is a resin with melamine rings terminated with multiple hydroxyl groups derived from formaldehyde. This thermosetting plastic material is made from melamine and formaldehyde. ...
veneer. Those types of
pressed wood
Pressed wood, also known as presswood, is any engineered wood building and furniture construction material made from wood veneers, wood shavings and particles, sawdust or wood fibers bonded together with an adhesive under heat and pressure.
See ...
boards are not very strong, and the screws of butt
hinge
A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...
s tend to pull out. A specialist hinge has been developed which uses the walls of a diameter hole, bored in the particle board, for support. This is a very common and relatively successful construction method.
A Forstner bit could bore the mounting hole for the hinge, but particle board and MDF are very abrasive materials, and steel cutting edges soon wear. A
tungsten carbide
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...
cutter is needed, but the complex shape of a forstner bit is difficult to manufacture in carbide, so this special drill bit with a simpler shape is commonly used. It has cutting edges of tungsten carbide brazed to a steel body; a center spur keeps the bit from wandering.
Adjustable wood bits
An adjustable wood bit, also known as an expansive wood bit, has a small center pilot bit with an adjustable, sliding cutting edge mounted above it, usually containing a single sharp point at the outside, with a
set screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distingu ...
to lock the cutter in position. When the cutting edge is centered on the bit, the hole drilled will be small, and when the cutting edge is slid outwards, a larger hole is drilled. This allows a single drill bit to drill a wide variety of holes, and can take the place of a large, heavy set of different size bits, as well as providing uncommon bit sizes. A
ruler
A ruler, sometimes called a rule, line gauge, or scale, is a device used in geometry and technical drawing, as well as the engineering and construction industries, to measure distances or draw straight lines.
Variants
Rulers have long ...
or
vernier scale
A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement unc ...
is usually provided to allow precise adjustment of the bit size.
These bits are available both in a version similar to an auger bit or brace bit, designed for low speed, high torque use with a brace or other hand drill (pictured to the right), or as a high speed, low torque bit meant for a power drill. While the shape of the cutting edges is different, and one uses screw threads and the other a twist bit for the pilot, the method of adjusting them remains the same.
Other materials
Diamond core bit
The diamond masonry mortar bit is a hybrid drill bit, designed to work as a combination router and drill bit. It consists of a steel shell, with the diamonds embedded in metal segments attached to the cutting edge. These drill bits are used at relatively low speeds.
Masonry drill bit
The masonry bit shown here is a variation of the twist drill bit. The bulk of the tool is a relatively soft steel, and is machined with a
mill
Mill may refer to:
Science and technology
*
* Mill (grinding)
* Milling (machining)
* Millwork
* Textile mill
* Steel mill, a factory for the manufacture of steel
* List of types of mill
* Mill, the arithmetic unit of the Analytical Engine early ...
rather than ground. An insert of
tungsten carbide
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...
is
brazed
Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Brazing differs from we ...
into the steel to provide the cutting edges.
Masonry bits typically are used with a
hammer drill
A hammer drill, also known as a percussion drill or impact drill, is a power tool used chiefly for drilling in hard materials. It is a type of rotary drill with an impact mechanism that generates a hammering motion. The percussive mechanism provid ...
, which hammers the bit into the material being drilled as it rotates; the hammering breaks up the masonry at the drill bit tip, and the rotating flutes carry away the dust. Rotating the bit also brings the cutting edges onto a fresh portion of the hole bottom with every hammer blow. Hammer drill bits often use special shank shapes such as the
SDS type, which allows the bit to slide within the chuck when hammering, without the whole heavy chuck executing the hammering motion.
Masonry bits of the style shown are commonly available in diameters from 3 mm to 40 mm. For larger diameters, core bits are used. Masonry bits up to long can be used with hand-portable power tools, and are very effective for installing wiring and plumbing in existing buildings.
A , similar in appearance and function to a hole punch or chisel, is used as a hand powered drill in conjunction with a
hammer
A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nails into wood, to shape metal (as w ...
to drill into
stone
In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...
and
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
. A star drill bit's cutting edge consists of several blades joined at the center to form a star pattern.
File:Drill masonry.jpg, 25×500 mm SDS-plus masonry bit
File:Drill tip masonry.jpg, Masonry bit tip
File:Quadro40max.JPG, Rebar resistant bit with four carbide cutters
File:Star_drill2.jpg, Star drill
Glass drill bit
Glass bits have a spade-shaped carbide point. They generate high temperatures and have a very short life. Holes are generally drilled at low speed with a succession of increasing bit sizes. Diamond drill bits can also be used to cut holes in glass, and last much longer.
PCB through-hole drill bit
A great number of holes with small diameters of about 1 mm or less must be drilled in
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
s (PCBs) used by
electronic equipment
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification a ...
with
through-hole
In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, either by ...
components. Most PCBs are made of highly abrasive
fiberglass
Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...
, which quickly wears steel bits, especially given the hundreds or thousands of holes on most circuit boards. To solve this problem, solid
tungsten carbide
Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...
twist bits, which drill quickly through the board while providing a moderately long life, are almost always used. Carbide PCB bits are estimated to outlast high-speed steel bits by a factor of ten or more. Other options sometimes used are diamond or diamond-coated bits.
In industry, virtually all drilling is done by
automated machines, and the bits are often automatically replaced by the equipment as they wear, as even solid carbide bits do not last long in constant use. PCB bits, of narrow diameter, typically mount in a
collet
A collet is a segmented sleeve, band or ''collar''. One of the two radial surfaces of a collet is usually tapered (i.e a truncated cone) and the other is cylindrical. The term ''collet'' commonly refers to a type of chuck that uses collets t ...
rather than a
chuck
Chuck is a masculine given name or a nickname for Charles or Charlie. It may refer to:
People
Arts and entertainment
* Chuck Alaimo, American saxophonist, leader of the Chuck Alaimo Quartet
* Chuck Barris (1929–2017), American TV producer
* C ...
, and come with standard-size shanks, often with pre-installed stops to set them at an exact depth every time when being automatically chucked by the equipment.
Very high rotational speeds—30,000 to 100,000
RPM
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
or even higher—are used; this translates to a reasonably fast linear speed of the cutting tip in these very small diameters. The high speed, small diameter, and the brittleness of the material, make the bits very vulnerable to breaking, particularly if the angle of the bit to the workpiece changes at all, or the bit contacts any object. Drilling by hand is not practical, and many general-purpose drilling machines designed for larger bits rotate too slowly and wobble too much to use carbide bits effectively.
Resharpened and easily available PCB drills have historically been used in many prototyping and home PCB labs, using a high-speed rotary tool for small-diameter bits (such as a Moto-Tool by Dremel) in a stiff drill-press jig. If used for other materials these tiny bits must be evaluated for equivalent cutting speed vs material resistance to the cut (hardness), as the bit's
rake angle
Rake angle is a parameter used in various cutting and machining processes, describing the angle of the cutting face relative to the work. There are three types of rake angles: ''positive'', ''zero'' or ''neutral'', and ''negative''.
* Positive ...
and expected feed per revolution are optimised for high-speed automated use on fiberglass PCB substrate.
Image:Two pcb bits.jpg, Two PCB
PCB may refer to:
Science and technology
* Polychlorinated biphenyl, an organic chlorine compound, now recognized as an environmental toxin and classified as a persistent organic pollutant
* Printed circuit board, a board used in electronics
* ...
drill bits.
Image:Box of 02in pcb bits.jpg, A box of #76 () PCB
PCB may refer to:
Science and technology
* Polychlorinated biphenyl, an organic chlorine compound, now recognized as an environmental toxin and classified as a persistent organic pollutant
* Printed circuit board, a board used in electronics
* ...
drill bits.
Installer bit
Fishing bit
Installer bits, also known as bell-hanger bits or fishing bits, are a type of twist drill bit for use with a hand-portable power tool. The key distinguishing feature of an installer bit is a transverse hole drilled through the web of the bit near the tip. Once the bit has penetrated a wall, a wire can be threaded through the hole and the bit pulled back out, pulling the wire with it. The wire can then be used to pull a cable or pipe back through the wall. This is especially helpful where the wall has a large cavity, where threading a
fish tape
A fish tape (also called a draw wire, draw tape, or an electricians snake) is a tool used by electricians to route new wiring through walls and electrical conduit.
Made of a narrow band of spring steel, by careful manipulation, the tape can be ...
could be difficult. Some installer bits have a transverse hole drilled at the shank end as well. Once a hole has been drilled, the wire can be threaded through the shank end, the bit released from the chuck, and all pulled forward through the drilled hole. These bits are made for cement, block and brick; they are not for drilling into wood. Sinclair Smith of
Brooklyn, New York
Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, be ...
was issued for this invention on January 25, 1898.
Installer bits are available in various materials and styles for drilling wood, masonry and metal.
File:Installer bit overview.jpg, A installer bit
File:Installer bit closeup 2.jpg, Closeup of installer bit. The fishing hole is visible in the flute in the center of the picture.
Flexible shaft bit
Another, different, bit also called an installer bit has a very long flexible shaft, typically up to long, with a small twist bit at the end. The shaft is made of
spring steel
Spring steel is a name given to a wide range of steels used in the manufacture of different products, including swords, saw blades, springs and many more. These steels are generally low-alloy manganese, medium-carbon steel or high-carbon steel ...
instead of hardened
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, so it can be flexed while drilling without breaking. This allows the bit to be curved inside walls, for example to drill through
studs from a
light switch
In electrical wiring, a light switch is a switch most commonly used to operate electric lights, permanently connected equipment, or electrical outlets. Portable lamps such as table lamps may have a light switch mounted on the socket, base, or i ...
box without needing to remove any material from the wall. These bits usually come with a set of special tools to aim and flex the bit to reach the desired location and angle, although the problem of seeing where the operator is drilling still remains.
This flexible installer bit is used in the US, but does not appear to be routinely available in Europe.
Drill bit shank
Different shapes of shank are used. Some are simply the most appropriate for the chuck used; in other cases particular combinations of shank and chuck give performance advantages, such as allowing higher torque, greater centering accuracy, or efficient hammering action.
See also
*
Drill and tap size chart
Below is a comprehensive drill and tap size chart for all drills and taps, imperial and metric, up to in diameter.
In manufactured parts, holes with female screw threads are often needed; they accept male screws to facilitate the building and ...
*
Drill bit shank
The shank is the end of a drill bit grasped by the chuck of a drill. The cutting edges of the drill bit contact the workpiece, and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement ...
*
Drill bit sizes Drill bits are the cutting tools of drilling machines. They can be made in any size to order, but standards organizations have defined sets of sizes that are produced routinely by drill bit manufacturers and stocked by distributors.
In the U.S., fr ...
*
Drill rod
Bar stock, also (colloquially) known as blank, slug or billet, is a common form of raw purified metal, used by industry to manufacture metal parts and products. Bar stock is available in a variety of extrusion shapes and lengths. The most common ...
*
Endmill
An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most m ...
References
Citations
Cited references
*
External links
Nomenclature
{{Cutting and abrasive tools
Hole making
Metallic objects
Woodworking tools