Center and spotting drill bits Center drill bits, numbers 1 to 6 Center drill bits are used in metalworking 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. 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).[10]
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 operation) with what is often a negligible loss in the co-axiality of features.
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 bits'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 the 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 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.
Center drill bits wander as easily as anything else in hand-held power drills—so for such operations, a center punch is often used to spot the planned hole center prior to drilling a pilot hole. However, a center drill bit works nearly as well as a spotting drill bit for most rigidly-clamped drilling operations, especially in softer metals such as aluminum and its alloys.
The small starting tip has a tendency to break, so it is economical and practical to make the drill bit double-ended.
Core drill bit Three-fluted core drill bit as used on castings A core drill bit can be a bit used to enlarge an existing hole. The existing hole may be the result of a core from a casting 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 reamers 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) which may occur in the product.
A quite different core drill bit is a hollow cylinder which will cut a hole with an annular cross-section. A diamond core drill bit is intended to cut an annulus 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, is retrieved and the strata in the core sampled are studied.
Countersink bit Main article: Countersink [edit] Ejector drill bit Used almost exclusively for deep hole drilling of medium to large diameter holes (about 3/4" up to about 4" 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 Main article: Gun drill A drill bit suitable for drilling holes much deeper than their diameter.
Indexable drill bit Indexable drill bits are primarily used in CNC 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 cutters, they use replaceable carbide, HSS 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 An 1/8 inch left-hand drill bit Left-hand bits are almost always twist bits and are predominantly used in the repetition 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 usage is less common than when specialized machines were required for machining tasks.
Screw extractors are essentially left-hand bits of specialized shape, used to remove common right-hand screws whose heads are damaged, making use of a screwdriver impossible. The drill bit is rotated counter-clockwise and will tend to jam in the damaged head and then turn the screw counter-clockwise, unscrewing it.
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 7⁄16 to 2.5 inches (11 to 63 mm). The tool holder usually has a coolant passage running through it.[11] They are capable of cutting to a depth of about 10 times the bit diameter. This type of drill bit can also be use 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 or brass because they have less of a tendency to "dig in" or grab the material.
Ultra Bor: The Ultra Bor drill bit has a thinner web and will substantially outperform cobalt drills in work hardening stainless steel applications. Ultra Bor drills are made of special hi-moly tool steel, which is much tougher than cobalt steel. The web on an Ultra Bor drill can be thinned considerably due to the toughness of the steel. Because of the thinner web, an Ultra Bor drill will penetrate stainless fast enough to continually cut beneath the chip which is hardening from deformation. This means the drill is cutting softer steel.
Source
http://en.wikipedia.org/wiki/Drill_bit#Metal_drill_bits
https://www.americanmadedrillbits.com
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 operation) with what is often a negligible loss in the co-axiality of features.
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 bits'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 the 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 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.
Center drill bits wander as easily as anything else in hand-held power drills—so for such operations, a center punch is often used to spot the planned hole center prior to drilling a pilot hole. However, a center drill bit works nearly as well as a spotting drill bit for most rigidly-clamped drilling operations, especially in softer metals such as aluminum and its alloys.
The small starting tip has a tendency to break, so it is economical and practical to make the drill bit double-ended.
Core drill bit Three-fluted core drill bit as used on castings A core drill bit can be a bit used to enlarge an existing hole. The existing hole may be the result of a core from a casting 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 reamers 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) which may occur in the product.
A quite different core drill bit is a hollow cylinder which will cut a hole with an annular cross-section. A diamond core drill bit is intended to cut an annulus 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, is retrieved and the strata in the core sampled are studied.
Countersink bit Main article: Countersink [edit] Ejector drill bit Used almost exclusively for deep hole drilling of medium to large diameter holes (about 3/4" up to about 4" 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 Main article: Gun drill A drill bit suitable for drilling holes much deeper than their diameter.
Indexable drill bit Indexable drill bits are primarily used in CNC 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 cutters, they use replaceable carbide, HSS 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 An 1/8 inch left-hand drill bit Left-hand bits are almost always twist bits and are predominantly used in the repetition 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 usage is less common than when specialized machines were required for machining tasks.
Screw extractors are essentially left-hand bits of specialized shape, used to remove common right-hand screws whose heads are damaged, making use of a screwdriver impossible. The drill bit is rotated counter-clockwise and will tend to jam in the damaged head and then turn the screw counter-clockwise, unscrewing it.
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 7⁄16 to 2.5 inches (11 to 63 mm). The tool holder usually has a coolant passage running through it.[11] They are capable of cutting to a depth of about 10 times the bit diameter. This type of drill bit can also be use 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 or brass because they have less of a tendency to "dig in" or grab the material.
Ultra Bor: The Ultra Bor drill bit has a thinner web and will substantially outperform cobalt drills in work hardening stainless steel applications. Ultra Bor drills are made of special hi-moly tool steel, which is much tougher than cobalt steel. The web on an Ultra Bor drill can be thinned considerably due to the toughness of the steel. Because of the thinner web, an Ultra Bor drill will penetrate stainless fast enough to continually cut beneath the chip which is hardening from deformation. This means the drill is cutting softer steel.
Source
http://en.wikipedia.org/wiki/Drill_bit#Metal_drill_bits
https://www.americanmadedrillbits.com