Metal drill bits are essential for metalworking. Different types of metal drill bits are available for different tasks. These types have various diameters, structures, shapes, and point angles which is essential for specific tasks.
The most used drill bit type is the twist drill bit and it is used for regular drilling tasks. Center drill bits are another type and it is used for pilot hole drilling. Spotting hole drill bits, counter sink drill bits, metal hole saw, gun drill bits, left-hand drill bits and ejector drill bits are the other types of metal drill bits. All these types are used for specific tasks. Hence you should have all of these when you are working with metals.
Normally, metal drill bits are made with HSS. Sometimes tungsten, cobalt, and carbide is also mixed with HSS in order to improve some characteristics. Some metal drill bits are made with cobalt and carbide. Those are used for drilling harder metals such as cast iron and stainless steel. The smallest metal drill bit size is 1/64 and the largest one will be 2″. The larger diameter metal holes will be drilled using a hole saw.
1. Twist Drill Bit
Twist drill bits are widely used drill bit structures for wood, metal, concrete, and many more. Due to the flute structure, those bits are named as twist drill bits. In order to use a wide range, twist drill bits are made with different materials. Mostly, HSS, cobalt, and carbide are used for drill bit materials.
Most of the twist drill bits are made using High-speed steel (HSS) because it needs superior qualities, including high hardness, wear resistance, and toughness. Some HSS bits have been combined with tungsten, molybdenum, cobalt, and vanadium in order to improve properties like thermal resistance, friction resistance and durability.
Twist drill bits are versatile drill bits geometry because it is used in many materials such as;
- Metals
- Wood
- Plastic
- Ceramics and composites.
And many more materials.
Due to its flute design, it can remove cutting material easily.
Overall, the geometry is designed to provide efficient material removal while reducing heat generation and wear on the drill bit. There are few geometrical designs to concern under the geometry;
- The point angle is the angle between the cutting edge at the tip of the drill bit.
- The helix angle is the angle between the flute and the axis of the drill bit.
- Flute length and width determine the ability to extract material and the quantity of heat that can be released during drilling.
- Shank diameter determines the hole size that can be drilled. Straight shank and hex shank are the types of the shank.
- Web thickness is the metal’s thickness in between the flutes. The strength and rigidity of the drill bit are determined by web thickness.
Twist drill bits can be used on corded or cordless drills, CNC (Computer Numerical Control) machines, drill presses, and magnetic drills can use twist drill bits. The twist drill bits are commonly offered in sizes between 1/16” to 1/2” inches and the average price range is $10 to $700.
Pros:
- Easy to use and has a minimal set type than other drill bits.
- A cost-effective drill bit.
Cons:
- Each material needs a different point angle. For soft material, it requires a lower angle, and for harder material requires a wide point angle.
2. Center Drill Bits
Center drill bits are often used to create pilot holes for larger twist drill bits or other cutting tools. The pilot hole guides to cutting tools to prevent wandering or slipping off-center.
A center drill bit is also made by HSS. Additionally, carbide, stainless steel, alloy, carbon, and cobalt includes in order to improve some characteristics. Drill presses, lathes, milling machines, and hand-held power drills can use as a drilling machines to drill materials including metals, plastics, wood, fiberglass, or carbon fiber.
Center drills have two common types.
- Type A – Forms a center hole with a single 60° chamfer
- Type B – Forms a hole with 2 chamfers, a 60° chamfer, and additionally a 120° chamfer at the start of the hole.
The center drill bit has three countersink angles;
- 60°
- 82°
- 90°
A common angle used in 60°. Flat head screws utilize an 82° design, and once again, the 90° leaves a chamfer afterward.
The geometrical designs of the drill bit;
- Point angle -600
- Flute – Short and shallow (It helps to clear chips and debris from the hole.)
- Shank – Straight, spiral
- Overall length: Typically, center drill bits are shorter than twist drill bits.
When concerned about the shank technology and durability of the center drill bits, high-quality steel is often used to make SDS Plus and SDS Max center drill bits, which are intended to withstand the severe stresses and pressures needed in drilling through hard materials like concrete and masonry.
The size is depending on body diameter, drill diameter, drill length and overall length and the price range of the center drill bit depends on the manufacturing material and process. Basically, it gets $1 to $100.
3. Spotting Hole Drill Bit
A spotting hole drill bit is used to accurately start the holes same as the “center drill bit”. Spotting hole drill bit is also made by HSS and carbide. There are coated and uncoated spotting drill bits in the market. Uncoated drill bits can easily sharpen.
Spotting hole drill bits are recommended to drill cast iron, plastic, steel, wood, and alloy steel by using a drill press, milling machine, lathe, and CNC drilling machines. So let’s check the things we should concern about spotted drill bits, including geometry, price and size range etc.
Flat bottomed and stepped spotted bit types are the types of spotting drill bit and here are a few geometrical designs to concern;
- Cutting angle – 900, 1200
- Flute – Slow spiral
- Flute length- Shorter than the regular drill bit
- Shank – Straight
- Overall length: Typically, center drill bits are shorter than twist drill bit.
The price range of a spotting drill bit in between $10- $300 in amazon.com. It depends on the quality and size of the drill bit. Normally, the smallest spotting drill bit has a 0.5 mm diameter and the largest has a 25mm or more.
4. Counter Sink Drill Bit
Counter sink drill bits are essential for removing broken bolts. It rotates anticlockwise direction. When the countersink drill bit is drilling on the broken bolt, it tends to loosen mostly. Hence it can remove easily. Counter sink drill bits are available in different materials in order to improve durability and performance.
Those are not used for continoiulsy. Those are for special tasks.
Countersink drill bit typically consists of HSS and carbide and it can drill;
There are few geometrical designs to concern;
- Point angle – 600, 820, 900, 1000, 1200
- Flute – Spiral, straight
Depending on the number of flutes in the bit, the material that can be drilled in is limited depending on the hardness.
Single flute – Has single cutting edge. Suitable for softer materials.
Two/ three flute – Has two cutting edges and suitable for harder materials.
Drill presses, bench drills, hand drill,s and conventional electric drills can use these drill bits.
When consider the size of the counter sink drill bits, those are shorter in length and available few sizes. The following drill bit sizes are common;
- 9/64
- 11/64
- 7/32
- 5/16
- 1/4
- 5/8 and 1/2 inch
5. Metal Hole Saw
The metal hole saw is another tool that can use for cutting “bigger” holes on metal surfaces. Producing a bigger twist bit is highly costly, and it needs higher maintenance costs. Hence the most suitable tool is a metal hole saw. Metal hole saws are made with HSS. Sometimes it includes carbide, diamond, tungsten, and many hard materials for using the hole saw in a wide range. Hence hole saws can be used on wood and metal widely.
However, it can use to cut softer materials, like wood, plastics and aluminum, etc.
Depending on the intended use, the size, spacing, and shape of the teeth on a metal hole saw can change. Metal hole saws typically have a cylindrical shape, and the open end has a circular cutting edge surrounded by teeth.
To enable the removal of the cut material as the saw slices through the material, the center of the hole saw is hollow. The cutting teeth can be either straight or helical (spiral-shaped), and they are often slightly inclined to improve cutting and reduce friction.
There are two types of metal hole saw depending on the bit type. “Arbor bit” and “pilot bit”.
The bigger size metal hole saws frequently use the shank technologies SDS-Plus and SDS-Max. With the help of these shank innovations, the hole saw may be connected securely and reliably to the rotary hammer or demolition hammer, enabling more effective drilling and lowering the possibility of the hole saw slipping.
Wide variety of sizes of metal hole saw drill bits are in the market. It is typically range in 1/2″ to 8″1/4 inches in diameter and it will $2 to $300.
6. Gun Drill Bit
Gun drilling is a deep hole drilling technique that produces holes in metal with high depth-to-diameter ratios by using a long, thin cutting instrument.
A gun drill bit is a long, straight drill bit and designed for deep hole drilling in metals (aluminum, brass, steel, bronze, titanium), plastics, and wood by using CNC machines’ drill presses. Among those, CNC machines are used widely.
HSS and solid carbide are the materials of the drill bit. The gun drill bit has a single and straight flute. A pointed tip of it helps to guide the bit during drilling and a chisel edge is useful to reduce cutting forces.
The shank is frequently cylindrical, smooth, and devoid of any flats or notches for the bit to rotate easily and lessens the chance that it may fall out of the drill chuck while it is being used.
There can we identify the range of sizes including; 1/8”, 5/32”, 3/16”, 7/32”, 1/4”,17/64”, 9/32”,15/16”, 3/8”,13/32”, 1/2”. The price of the gun drill can range from $30 to several hundreds of dollars.
7. Ejector Drill Bit
Ejector drilling is one of three major methods for deep-hole drilling. Deep hole drilling is defined by a ratio of depth to a diameter that exceeds five.
Ejector drill bits can be used to drill holes as deep as 19mm to 102mm (3/4 to 4 inches) and can use in, oil and gas industry, aerospace applications, engines, plastic injection molding, and landing gear. Therefore, it can use to drill,
- Plastics
- Construction steel
- Heat treated steel
- Cast iron (alloyed and unalloyed)
- Aluminium and Aluminium alloys
Both traditional and CNC machines use ejector drills.
There are few geometrical designs to concern;
- Point angle – 1200
- Flute – Parallel, straight
- Ejector groove – A small channel that runs along the length of the drill bit.
- Shank – Hex
The setup for ejector drilling includes,
- A pair of concentric tubes forming the drill tube,
- A drill head to perform the actual metal cutting,
- A rotary connector (sometimes called a coolant inducer) supplies coolant from the spindle through the drill tubes
- An adapter on the front of the spindle through which the coolant and chips exit.
Ejector drill bits are little bit expensive than the regular drill bit. It may $30 to $500.
8. Left-Hand Drill Bit
The left-hand drill bits’ flutes run in the opposite direction (counterclockwise) and it is best to remove broken bolts and studs. The manufacturing materials of left-hand drill bit are;
- HSS
- Stainless steel
- Alloy steel
- Cobalt
- Chrome vanadium steel
There are a few geometrical designs to concern;
- Point angle – 1180, 1350
- Flute – Parallel, straight, Spiral
- Ejector groove – A small channel that runs along the length of the drill bit.
- Shank – Straight, spline
- Web thickness
Left-handed drill bits could free the fractured stud while simultaneously keeping the broken component from being further tightened, thereby doing away with the requirement for a screw extractor.
Left-hand drill bits are a little bit more expensive than the regular drill bit. It may be $30 to $1000 for a drill bit set ranging between 1/16” to ½”
Pros:
- No Pilot Hole required
- It gives rounder and more accurate holes
Choose right size and type of bit for the project is essential and suitable drilling speed and pressure and suitable lubricant is too important to reduce the heat generation and help to prolong the lifespan of drill bit.
