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brad-point-drill-bits-for-metal-77 November ; 11 : Clear Coated. A step bis bit is a drill bit that has the tip ground down to a different diameter. Clear All. For larger bits, special grinding jigs are available. Maximum Drilling Depth. Hex-Shank Drill Bits.

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. A unibit often called a step drill bit is a roughly conical bit with a stairstep profile. 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 [10] 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 patented in Unibit is a trademark of Irwin Industrial Tools. Although it is claimed that the stepped drill was invented by Harry C Noakes it was in fact first produced by Bradley Engineering, Wandsworth, London in the s and named the Bradrad.

It was marketed under this name until the patent was sold to Halls Ltd. 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.

Center drill bits , occasionally known as Slocombe 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. 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 a negligible loss in the co-axiality of features usually total indicator reading TIR less than 0.

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. 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 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 is often used to spot the hole center prior to drilling a pilot hole. A bit used to enlarge an existing hole is called a core drill bit. 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.

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 hollow cylindrical bit which will cut a hole with an annular 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.

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. 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. 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 drills 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.

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 or ceramic inserts as a cutting face to alleviate the need for a tool grinder. One Brad Point Drill Bits For Metal Volume 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 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 use 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 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.

A spade drill bit for metal is a two part bit with a tool holder and an insertable tip, called an insert. The tool holder usually has a coolant passage running through it. This type of drill bit can also be used to make stepped holes.

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. 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 6—14 in — mm and hole depth from 12 in mm up to 71 feet 22 m. The lip and spur drill bit is a variation of the twist drill bit which is optimized for drilling in wood. It is also called the brad point bit or dowelling bit. 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 lip and spur drill bit is another solution: The centre 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.

The sharp point of the spur simply pushes into the soft wood to keep the drill bit in line. Metals are typically isotropic , and an ordinary twist drill bit shears the edges of the hole cleanly. Wood drilled across the grain has long strands of wood fiber. These long strands tend to pull out of the wood hole, rather than being cleanly cut at the hole edge.

The lip and spur drill bit has the outside corner of the cutting edges leading, so that it cuts Brad Point Drill Bits For Metal Engineering 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 them pull messily out of the timber. Lip and spur drill bits are also effective in soft plastic.

Conventional twist drill bits in a hand drill, where the hole axis is not maintained throughout the operation, have a tendency to smear the edges of the hole through side friction as the drill bit vibrates. In metal, the lip and spur drill bit is confined to drilling only the thinnest and softest sheet metals in a drill press.

The bits have an extremely fast cutting tool geometry: no point angle and 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. Lip and spur drill bits are ordinarily available in diameters from 3—16 mm 0.

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". 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 to take the back spindles, or similar round-tenon work when assembling furniture frames in green woodworking 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 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 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.

Bits are commonly available in sizes from 8—50 mm 0. Sawtooth bits are available up to mm 4 in diameter. Originally the Forstner bit was very successful with gunsmiths because of its ability to drill an exceedingly smooth-sided hole.

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 lip and spur 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. Skip Navigation Sears home. Drill Bits 7 items. Refine Your Search clear all Your Selections:.

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