A Buying Guide for Drill Bits

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A Buying Guide for Drill Bits

When the phrase "drill bits" comes to mind, most people picture a specific kind of drill bit: the Morse or twist bit that is designed for metal drilling but is used for drilling just about everything. If a tool kit has only one set of drill bits, it is almost certain they are twist bits.

Remarkably, drill bits are as specialised as any other piece of industrial design. Some are created for ripping large holes through framing studs; some for nipping out a tiny bud to countersink a screw. Drill bits are designed specifically for wood, metals up to stainless steel, masonry, and stone. A specialised drill, the hammer drill, is even designed to facilitate the removal of masonry fragments from the hole whilst drilling.

Purchasing drill bits, then, requires determining how they are to be used, what materials are to be drilled, what kind of drill is to be used, and what size of holes are needed. Considering these issues allows a buyer to confidently shop for drill bits in a local ironmonger's or in an online marketplace such as eBay.

Determine Type of Drill to Use

Many drill bits fit into most kinds of drills. A standard power drill and standard hand drill both are usually chucked for the same bits, allowing users to own a single set of bits for each kind of work that needs to be done. The hammer or SDS drill for masonry is an exception. It uses specific bits to handle its unusually tough work.

Hammer or SDS Drills for Masonry

The hammer drill or SDS drill is a specialised power drill for masonry work, designed to drill, cut, and demolish masonry as needed. A typical hammer drill offers three modes of action: rotary, rotary with impact, and chisel action with rotary stop. Both drill bits and chisel bits are used.

The way the action functions in drilling stone or masonry is that the hammer action crushes the masonry ahead of the bit and the rotary action draws the fragments out of the hole.

Power Drills

Power drills are standard tools for home and professional users. They are produced with several power modes: cord power drills, battery power drills, and compressed air power drill.

Drill Press

A drill press is a drill permanently mounted in a vertical position over a table where the materials being drilled may be securely fastened in a vice or set against a positioning bar, allowing for accurate location of the drilled hole or holes. The drill mount is designed to permit precise specification of drill hole depth as the drill is lowered along a shaft to a predetermined height. Drill press speeds are often too high for 12 mm drill bits and those larger, although variable speed drill presses may be found with speeds as slow as 200-300 rpm, which are appropriate for larger bits.

Hand Drills

While drill bits are often considered a power tool accessory, changeable drill bits are also used in hand drills. Some of the bits often specialised to the hand woodworker include countersink bits used in creating the dip used to conceal a screw head behind a trim.

Determine Material to Drill

The kinds of drill bit selected vary in part depending on the material to be drilled. Both the shape of the drill bit and the material from which it is made may be different for bits designed to be used in drilling wood, plastics, masonry, ceramics, metals, and stone. The hardest drill bits, those made with tungsten carbide, are able to handle virtually any material.

Drill Bit Material

Drill bits may be made from a number of metals, each of which has advantages for specific applications. As the metal becomes more rigid, it also becomes more brittle and less able to be sharpened when it dulls. The table below summarises the characteristics of common drill bit materials and their preferred applications.

Drill Bit Material

General Characteristics

Preferred Applications

Low Carbon Steel

Inexpensive, require sharpening or replacement

Wood, soft plastics

Chrome Vanadium Alloy or VA

[1]

Wood

High Carbon Steel

May lose temper and cutting edge if overheated

Wood, metal

High Speed Steel or HSS

Preferred among production workers because of ability to retain temper at very high speeds

Wood, metal, plastics, most ceramics

Cobalt Steel Alloy

High performance and longevity; more brittle than HSS

Metals including stainless steel

Titanium and Other Ceramic Coatings: Black Oxide, Titanium Nitride, Titanium Aluminium Nitride, Titanium Carbon Nitride

Give softer bits higher performance

More difficult materials than base bit could handle

Tungsten Carbide and Carbide Tipped

Strongest, hardest of all bits; all-carbide is very expensive; carbide-tipped is very effective at more reasonable price

Virtually any material including stone

The selection of bit material depends on the kind of material to be drilled. The professional contractor may value the ability to resharpen a dull bit but the average home repair person is likely simply to replace it.

Typical Drill Bits

Drill bits are shaped to accomplish specific tasks. Some bits are more flexibly used across a range of activities than others, while some are very specific in what they are designed to accomplish. Some common drill bit designs are described below, along with the tasks to which they are best suited.

Twist Bit

Also known as a Morse bit, the twist bit is the most common kind of drill bit. It is designed for metal drilling but may be used for drilling virtually every kind of material. Its high speed makes it less appropriate for precision drilling, however.

Split Point Bit

The split point bit is designed for metal drilling. It is almost identical to the twist bit but has a split point to help it maintain centre in difficult materials. The various points and angles are somewhat sharper to make it more effective in metals.

Brad Point Bit

The woodworker's brad point bit has a sharp tip with broad outward curves to the cutting edges. The tip maintains the centre while drilling; the isolated cutting edges create a smoother hole.

Countersink Bit

The countersink bit produces a "pocket" into which a screw head may be set at, or below, the surface of the working material.

Auger Bits

Auger bits bore long, rough holes through wood. They look like long spirals because they are designed not only to drill out material but to clear out the drilled material as they go. A common use is drilling through framing studs.

Spade or Paddle Bits

The spade bit is named for its shape. It is also designed to drill holes in wood.

Hole Saw Bits

The two-part hole saw bit includes a twist bit and a circular saw ring with serrated teeth. These teeth cut very smooth holes. They may be used with hand drills as well as power equipment.

Buy the Bit or Buy the Set: Hole Size

Most bit shapes are offered in sets that provide a range of diameters. This allows the user to select the bit appropriate to the moment's need. The smallest bits in the market are measured in ten-thousandths of a millimetre: 0.0125 mm. The largest bits for standard drills are tapers that can achieve holes of 3.8 cm. And just for the record, the largest drill bit ever was the 95 m auger used to drill a subway tunnel in Leipzig, Germany.

Some of the kinds of bits more likely to be sold as singles include: masonry drill bits, spade drill bits; auger drill bits, also known as lip and spur bits, tile drill bits; countersink bits; large diameter bits; and extra-long bits. Bits marketed in Imperial measures instead of metric are also more likely to be offered in singles.

Speciality Drill Bits for Unusual Purposes

In addition to the various bits noted above, several kinds of specialty bits may also be required for some specific purposes. These are, in certain cases, adapted to a specific type of drill only.

Rotary Burr Drill Files

Rotary burr drill files are used for smoothing rough edges that remain on a project. One way they might be used is to smooth the interior of a drilled hole in metal or wood. However, the wide variety of shapes, sizes, abrasive textures of these files allows them to be used for many applications such as routing, carving, sanding, and polishing. These are frequently used with smaller, more manoeuvrable devices like the Dremel rotary tool.

Chisel Drills

Chisel drills are designed for use with the SDS or hammer drill. They come in several shapes, including point, gouge, and groove, for use in masonry drilling and destruction.

Buying Drill Bits on eBay

Shopping for drill bits on eBay is an easy process because the range of options is large. A buyer may use the search window to specify the bit material desired, such as "carbide drill bit", the kind of bit desired, or the manufacturer, if there is a preference. Most bits are offered in sets, so it is not easy to specify the diameter of bit desired. However, it is easy to find sets of bits that include the desired diameter. And for such speciality bits as "auger drill bits", single bits in specified diameters may be found by searching for such terms as "auger drill bit 235 mm".

Buyers may feel confident in the seller when they check seller feedback, located on the product page. This rating is provided by past purchasers and indicates a seller's history of quality service. Top-rated sellers, noted with a ribbon, are high volume vendors who have a history of providing quality service to the customer.

Conclusion

Drill bits turn out to be far more individual than most people's introduction to the first set suggests. Drill bits are made of a wide range of materials that suit them to drill different materials. They are designed in diverse shapes to accomplish different tasks. Their sizes vary and they are often offered in sets to allow the user to select the best size "on the fly".

Several different kinds of drills are commonly used, most of which accommodate all of the typical kinds of drill bits. The hammer or SDS drill used with stone and masonry is the exception: it requires specialised bits to handle the pressure of its pounding action and also accommodates chisel bits for masonry demolition.

Bits may be purchased individually or in sets that include a range of stepped sizes. The latter is often most convenient, although some specialised bits may need to be purchased as singles. These include bits that are extra long, have very large diameters, or are used for uncommon purposes such as drilling tile. Buyers who seek drill bits for any purpose are able to locate a range of bits to meet their needs in the eBay marketplace, where an extensive selection is always available.


 
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