Choosing the right drill bit

Drill bits are cutting tools used to remove material to create holes, almost always of a circular cross-section. Drill bits are available in different types and diameters depending on the type of material to be drilled and the size of the hole required.

 

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  • How to choose a drill bit?

    To choose the right drill for your activity, you must first consider the material to be drilled. Every material has a specific hardness and mechanical properties. This is why they are many different drill bits.

    The main criteria to consider before choosing your drill are the following:

    • Drill bit material: HSS or tungsten carbide
    • The fit: will depend on the machine used.
    • Diameter
    • Drill bit type: twist, step, reamer, center, conical, insert
    • Drill bit coating
    • Bit angle
    • Bit length (short or long)

    Selection criteria:

    • Material
    • Drill bit type
    • Fit
    • Diameter
    • Drill bit coating
    • Bit angle
    • Bit length
  • Should you choose a solid drill bit or a drill with interchangeable inserts?

    Allied Machine & Engineering insert drill bit

    Insert drill bits are used for drilling large diameter holes. They are usually found on machine tools. They can be used at a much higher speed than solid drill bits and on a wider variety of materials. They are more economical because you can replace the inserts when they become worn. Replacing an insert can be done very quickly. They also have several cutting surfaces per insert.

    Solid drill bits have the advantage of being more rigid. They are suitable for small diameters and tight tolerances. If they become worn, they can easily be reset (sharpened).

  • Which drill bit should you use for which material?

     The drill bits listed below are the most commonly used.

    • For wood: these types of drill bits can be used on any wood, whether it is softwood, hardwood, veneer or plywood.
    • For metal: these drill bits are used to drill any kind of metal. When it comes to drill bits for metal, inserts are only used for machine tools.
    • Drill bits for masonry: these steel drill bits have a brazed tungsten carbide tip.
    • For tile and glass: these drills bits look like small spears. They are characteristically used with a low drilling speed .
    Drill bit type

     

    Main fit

     

    Drill bit material

     

    Quality

     

    Specific characteristics Drilled materials
    Characteristic Quality
    Masonry drill bits Smooth Shank, SDS+, SDS Max Tungsten carbide From

    ***

    to

    **** 

    (depending on the percentage of carbide)

    2 cutting edges ** Concrete, Reinforced concrete, Concrete blocks, Stone
    3 cutting edges ****
    4 cutting edges ******
    Carbide ****** Carbide tip ******
    Drill bits for metal Smooth and hexagonal shank HSS ** Rolled steel (occasional use) or hardened steel (regular use) Non-ferrous metals
    HSS-R **
    HSS-G ***
    Titanium **** Grinding drill bit

     

    Tungsten carbide ****
    Cobalt ***** Grinding drill bit Ferrous and non-ferrous metals, Stainless steel etc.
    Solid carbide ****** Grinding drill bit Full steel
    Drill bits for machine tools Cylindrical shank (ISO 9766)

    Morse taper

    SDS

    with carbide inserts ****** Interchangeable inserts Ferrous and non-ferrous metals
    Chamfering drill bit
    Countersink
    Chamfering countersink
    HSS
    Drill bits for wood Smooth and hexagonal shank Steel **** Flat head Woodworking
    3 point
    Spiral head Carpentry
    Tile head Smooth shank Tungsten carbide *** Conical head Tiles, Ceramics, Roof tiles
    Glass head Diamond **** Conical head Glass

    Drill bit types:

    • For wood
    • For metal
    • For masonry
    • For tile and glass
  • What material should you choose for your drill bit?

    Walter drill bits

    Drill bits and cutting inserts come in a variety of materials, each with its own advantages and disadvantages.

    • Hard metal drill bits: for general use.
    • HSS (high speed steel) drill bits: higher speed machining, versatile and less expensive than carbide tools.
    • Carbide drill bits: have a cutting speed four times higher than HSS drill bits, but they are fragile. It is difficult to sharpen them.
    • Ceramic drill bits: for high temperatures and even higher cutting and feed speeds without chip formation on the tool. These are suitable for refractory materials but cannot be sharpened.

    There are also several types of coating:

    • Diamond coating: for abrasive materials such as graphite. It has a higher hardness than CBN layers for example. It improves wear resistance.
    • CBN coating: for treated steel products above 45-50 HRC, gray iron, hardened chrome alloyed cast iron, cobalt, nickel and iron based anti-wear alloys. It has a better resistance to high temperatures than diamond coatings.
    • PCD coating: for aluminum, non-ferrous and precious metals (silver and gold), carbide (before sintering), plastics and rubber, titanium alloys.
  • What drill geometry should you choose?

    ALFRA step drill bit

    There are several drill geometries available:

    • Twist drill bit: this is the most common type of drill bit, it is used to make holes in wood, metal, plastic and many other materials. Most are made of high speed steel (HSS). However, they are not suitable for masonry. In general, twist drill bits do not need pilot holes because they are self-centering. Since these are general purpose bits, they are a good choice if you don’t have a specific project in mind.
    • Step drill bit or unibit: this drill bit is conical in shape, with a stairstep-like pattern. You can drill holes of different diameters in wood, metal and plastic, all with one drill bit. This type of drill bit is the best suited if you want to drill sheet metal.

    There are drill bits with specific geometries depending on the materials to be drilled.

    • Drilling in wood: drill bits designed for drilling wood (or wood drill bits) usually have a sharp tooth at the head of the bit to facilitate centering.
    • Drilling metal: drill bits or hole saws include a core bit and a point to guide them. You should always slow down the speed to prolong the life and performance of the core bit.
    • Masonry drilling: the masonry drill bit is suitable for brick and concrete. It is easy to distinguish in your toolbox because its tip is often made of tungsten carbide. Masonry bits are always used with rotary hammers or hammer drills.

    There are three types of shanks for machine tool drill bits:

    • The cylindrical shank with parallel flat, standard ISO 9766.
    • The “Morse taper” shank, which requires a conical chuck corresponding to the Morse taper.
    • The SDS shank, which requires a retractable SDS chuck of the same size for automatic assembly and clamping.
  • What are the standards for drill bits?

    The main standards for drill bits are outlined below:

    • DIN 333 standard: 60° center drill bits, R, A and B types
    • DIN 338 standard: shot cylindrical drill bits
    • DIN 340 standard: long cylindrical drill bits
    • DIN 345 standard: Morse taper drill bits
    • DIN 1869 standard: extra-long cylindrical drill bits
    • DIN 1870 standard: extra-long Morse taper drill bits
    • DIN 1897 standard: extra short cylindrical drill bits
    • DIN 6537 standard: solid twist drill bits in hard metals with cylindrical shank
    • DIN 6539 standard: solid drill bits in hard metals with cylindrical shank
    • DIN 8037 standard: cylindrical drill bits with carbide inserts for metallic materials
    • DIN 8374 standard: step drill bits with cylindrical shanks for through holes and chamfers for countersunk head screws
    • DIN 8378 standard: step drill bits with cylindrical shank for tapping pilot holes
    • DIN 8379 standard: step drill bits with Morse taper shank for tapping pilot holes
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