Drill bit structure: These features are found on every twist drill

Twist drill bits or helical twist drill bits are familiar to all of us and if you are an attentive reader of our blog, you can also distinguish quite well which drilling tool is suitable for which application. But do you also know exactly why not every material can be machined with every drill? At BAER we like to – forgive us the pun – drill a little deeper and enjoy finding out how things are exactly connected.

And that is why we are dealing today with the construction of a twist drill bit. Because to optimally adapt a tool to the material being machined, there is much to consider, especially in metal machining – from the hardness of the material to chip formation. Only in this way can a perfect borehole be created. So if you want to know exactly what's going on when drilling in future, then by all means read on and let us introduce you to the wide world of drill bit geometry.

Why it's worth familiarising yourself with tool construction

Of course, with the correct drill bit, you'll be able to create holes without ever having heard terms like rake angle or chisel edge. So you don't necessarily have to concern yourself with the exact construction of your tool – especially not when everything is running smoothly. However, things become interesting when boreholes don't turn out as hoped. If you'd like to investigate the causes in such cases, it can certainly be advantageous if you can draw on a solid knowledge base right away.

The selection of the drill bit is crucial for the drilling result, as different materials place different demands on the tool. Especially for ambitious projects or if you like to work with unusual materials or want to express your creative side, the necessary knowhow about the construction of twist drill bits can be the deciding factor and make the difference between success and failure.

How a twist drill bit is constructed

The cutting edges and the flutes are the characteristic attributes that make a twist drill bit a twist drill bit. And to position these attributes relative to one another, the angles at strategically important points are crucial. Let's take a closer look at this:

The cutting edges at the tip of the drill bit

Let's start with the main cutting edge at the tip of the drill bit. This is where the actual drilling process takes place. Twist drill bits can have a different number of cutting edges depending on their design and intended use, with most twist drill bits being double-edged. Three-edged drill bits offer higher stability and lower vibrations, which result in more even and smoother borehole walls.

Centrally at the highest point of the drill tip sits the chisel edge. The chisel edge connects the two main cutting edges and has no cutting effect, but influences the pressure and friction when penetrating the workpiece. The chisel edge is modified by the point or grinding. Various shapes are possible here, which affect centring and spot drilling.

Along the flutes, the secondary cutting edges also run. The secondary cutting edge of the twist drill bit releases and cuts chips that have become jammed on the workpiece, and thus also has an important role to play in ensuring smooth drilling operation.

Flutes are important for chip evacuation

When machining, chips are produced and they must be removed from the borehole. To create space for this, the twist drill bit has flutes, which can be of different widths and depths. A wider flute profile improves chip evacuation and reduces heat generation, which extends the service life of the drill bit.

The minor diameter of the drill bit is directly related to the shape of the flutes – the deeper the flute profile, the thinner the core. The core thickness of the twist drill bit is crucial for stability and suitability for higher torques and harder materials. It is therefore important to carefully weigh the characteristics of the different designs and select the best combination for the intended application.

Point angle and along the flute

Angles play a role in two locations on the drill bit: at the point and along the flute.

The point angle at the head of the twist drill bit is crucial for centring in the workpiece. A small point angle facilitates centring in the workpiece, whilst a larger point angle reduces drilling-in time. The point angle is typically 118° for softer materials and up to 140° for hard materials.

The rake angle (also known as side rake angle, helix angle or spiral angle) determines the type of chip formation and chip evacuation during the drilling process. A larger helix angle promotes effective chip removal when working with soft, long-chipping materials, whilst smaller angles are suitable for hard, short-chipping materials. A distinction is usually made between Type W with a short helix, Type N with a standard helix and Type H with an extended helix.

What about other drill bit types?

We talk all the time quite naturally about twist drill bits, but of course there are other drill bit types. Often these are more specialised items intended for specific drilling tasks. A Forstner bit, for example, does without a flute, and a countersink doesn't need one either. In these two examples, either not many chips are produced, or they find their way out in the open due to the large diameters and shallow drilling depths, even without flutes. A step drill bit is specially designed for use in sheet metal and plates and is geometrically configured for this purpose. And of course, there's also the particularly exciting field of screw taps, which you should definitely look into more closely...

You can start right here in our BAER online shop. We have twist drill bits for every application and, of course, an extensive range of screw taps waiting for you. In addition, you will find numerous other products that make work almost effortless. Convince yourself! And if you have any questions or problems, our customer service is always available to help you.