TWIST DRILL BITS – HOW TO IDENTIFY WHICH ONE IS USED FOR WHAT

The most common type of drill bit is the twist drill bit.

At first glance, all twist drill bits look the same: on one side there is the part used to clamp the tool into the machine, on the other side there is the tip, and between them a spirally twisted flute.

However, if you look more closely, you will find that there are some differences between twist drill bits after all. These are details that clearly show what you can expect from them and what material, or which machines, they are intended for.

So how can you find out what the drill bit you have just found in your workshop can be used for? How can the individual types be distinguished from one another?

TWIST DRILL BITS FOR METAL

Typical appearance of a metal drill bit:

• The tip is ground into a cone
• The cutting edge has 2 sharp cutting edges
• The flute is ground along the sides
• The shank is either cylindrical, or for larger diameters it may have the shape of a Morse taper (for pillar drills)
• They are made of high-speed steel (HSS)

The drill bits are suitable for drilling into iron, steel, cast iron, brass, aluminium, copper and other non-ferrous metals.

They can also be used for drilling into plastic and wood.

For stainless steels and alloy steels with higher hardness, it is necessary to use drill bits made of cobalt-alloyed steel (HSS-Co.), or drill bits with a protective coating (TiN, TiAlN, etc.).

This is what a metal drill bit looks like:

TWIST DRILL BITS FOR WOOD

You can recognise all types of wood drill bits (not only twist drill bits) by the centring point located in the middle of the tip.

The centring point may sometimes also be threaded – see, for example, auger drill bits.

Typical appearance of a wood drill bit:

• The centre of the tip is fitted with a centring point
• There are 2 ground cutting edges on the sides of the tip
• The flute is ground along the sides
• They are made of tool steel, carbon steel or chrome-vanadium steel alloys, but also of high-speed steel (HSS), or they may have a carbide tip
• The shank is usually cylindrical or hexagonal (for use in cordless tools)

The drill bits are suitable for drilling into all types of hard and soft wood, chipboard and plywood.

This is what a wood drill bit looks like:

TWIST DRILL BITS FOR MASONRY AND CONCRETE

While a drill bit “cuts away” the material when drilling into metal or wood, when drilling into masonry and concrete the drill bit strikes the material and breaks it apart. The flute then removes the resulting dust and debris.

Typical appearance of a masonry and concrete drill bit:

• A carbide plate is inserted and brazed into the tip
• The carbide may be designed as a two- to four-cutter, and its cutting edges are blunt or ground
• The flute is not ground along the sides
• They are made of tool steel, carbon steel or an alloy of chromium, nickel and molybdenum
• For use in impact drills and cordless screwdrivers, the shank is usually cylindrical or hexagonal
• For use in electro-pneumatic hammers, the drill bits have a quick-release shank system (e.g. SDS-plus, SDS-max)

The drill bits are suitable for drilling into concrete, stone, masonry, brick and lightweight building materials.

This is what a masonry and concrete drill bit looks like: