Metal drill bits

Metal drill bits: what you need to know

Metal drill bits are high-strength cutting tools which are designed for making holes or recesses in different materials. They have a sharp tip and special cutting edges due to which they can bore a workpiece, when rotating.

What are the types of metal drill bits?

By design:

• Spade drill bits. They are intended for reaming large holes by drilling. Their working part is made in the shape of a plate. Swarf removal isn’t provided.
• Twist drill bits. The most widely spread. They are made as a rod with spiral grooves which are used for removing swarf from the working area and also contribute to the cooling of the part. There are right-hand and left-hand metal drill bits. The latter ones are intended for drilling out stuck or damaged fasteners.
• Hole saws. They are made as a hollow cylinder with teeth on its edge which are usually covered with diamond coating. Used for fast drilling of holes of a large diameter. Intended for thin metal sheets.
• Unibit drill bits (step drill bits). They are suitable for boring holes of different diameters. They often have markings on them to define the precise size of the hole.
• Center drill bits. They are double ended. Used for making marks.

By the method of production:

• Solid drill bit. They are made as a solid element produced of only one material.
• Welded drill bits. Their shank is usually made of a softer material, while the cutting part – of a hard one.
• Indexable drill bits. Comprise a body and changeable plates or heads. Suitable for heavy workloads. Ideal for processing flat bottom holes.

By the shape of the hole:

• Cylindrical. They have the same diameter throughout the entire drilling depth.
• Conical. These are tapered bits.

By the material:

• Carbon steel bits. They are inexpensive. Prone to corrosion. Non-elastic.
• Compound steel bits. Perfectly combine durability, stiffness, elasticity and wear resistance. Characterised by a low price.
• Hard alloy bits. Characterised by a high drilling speed.

Tips on using metal drill bits.

It is necessary to choose an appropriate drilling mode to ensure the longest possible service life of the tool. For example, the optimum speed for a drill bit of 3 mm diameter is 400 rpm.

It is not recommended to use dull accessories. You should use special equipment for sharpening the cutting edge. When doing this, you should consider the material you’re going to work with. For instance, for drilling a copper workpiece, it is required to sharpen the bit at an angle of 100°, while for working with steel you’ll need the angle of 140°.

In order to make a straight hole, it is necessary to mark the centre of the future hole with a punch. You can also use a special centre metal drill bit. You should hold the tool so that the cutting part would be positioned at a right angle to the processed workpiece.

You shouldn’t apply too much force to the drill. When making open-end holes, you need to gradually reduce the effort. To avoid overheating of the tool it is recommended to put it occasionally into a vessel with cold water or machine oil. It is not allowed to touch the moving parts: there is a risk of getting injured or burnt.

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