Ground vs. rolled – What is the difference between ground and rolled twist drills?
Not all twist drills are the same. It is not only the material (e.g., HSS or carbide) that is decisive, but above all the manufacturing process—ground or rolled. What exactly does that mean? And which drill is suitable for which application?
The terms ground and roll-rolled refer to the manufacturing process of twist drills, i.e., how the spiral flute is created.
Rolled drills
Rolled drills are made by rolling a red-hot round metal rod made of high-speed steel (HSS) until it forms a spiral shape. This results in rounded edges and a rather imprecise concentricity of the twist drill.
The material structure of the HSS remains largely intact, which means that the drills remain tough and elastic. The spiral drills can be recognized by their dark gray to black color and the slightly rounded transitions from the shaft to the groove.
Advantage
Because the structure of the material remains largely intact, rolled drills have greater elasticity and robustness, which makes it possible to work with cordless screwdrivers, for example on construction sites.
Disadvantage
Rolling creates tolerances in concentricity, which affects precision – especially with tight fits or in hard materials. This makes them more affordable.
Typical characteristics
- Higher toughness, more resistant to breakage
- More cost-effective to manufacture
- Good for manual applications or soft materials
- Lower dimensional accuracy compared to ground drills
Ideal for: Softer steels, non-ferrous metals, structural steel, hand drilling, assembly applications.
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Ground drills
When manufacturing ground twist drills, the flute is cut into the metal blank (HSS or higher alloy) using a grinding wheel. This process gives ground drills extremely sharp edges. Manufacturers usually abbreviate them with -G (for ground): HSS-G.
Ground twist drills usually have a shiny silver inner surface of the spiral. The transition between the shank and the flute has sharp edges.
In contrast to rolled twist drills, these twist drills are often coated to extend their service life.
Advantage
The twist drills retain their shape, resulting in a long service life and high precision.
Disadvantage
Their manufacturing method can damage the material structure and cause the drill to break more quickly. For this reason, they are mainly used in stationary drilling machines to perform precise and accurate work.
To prevent the ground twist drill from overheating, it is important to cool it sufficiently during use. There are 5 reasons why cooling is beneficial.
Typical characteristics
- High concentricity
- Clean, precise drill holes
- Uniform chip removal and evacuation
- Particularly good for hard or tough materials
- Available in HSS, HSS-Co 5, or coated (e.g., TiN, TiAlN)
Ideal for: Stainless steel (with HSS-Co 5 drills), high-alloy steels, precise drilling, series production, machine processing.
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At a glance – rolled vs. ground
| Feature | Rolled | Ground |
|---|---|---|
| Manufacturing | Shaping by rolling | CNC grinding, ground from solid material |
| Dimensional stability | Lower | Very high |
| Precision | Lower, more tolerant | Very high, precise cutting |
| Service life | Good for soft materials | Higher for hard materials |
| Breaking strength | Tough, more resistant | Rather brittle |
| Price | Cheaper | More expensive |
| Ideal for | Structural steel, non-ferrous metals, simple applications | Stainless steel (for HSS-Co 5 drills), precision metalworking |
When should you choose which drill?
Choose rolled twist drills if...
- you are drilling simple holes in soft materials (e.g., structural steel)
- cost-effectiveness is important
- you mainly work with a hand drill
- precision is not important
Choose ground twist drills if...
- the holes need to be exact (ideal for precise drilling in metal, stainless steel, and hard materials)
- you are working with hard or tough materials
- you want a longer service life
- you are working with a machine or CNC
Tips for use
- Grind drills should generally be cooled
- Rolled drills should be replaced regularly, as they become blunt more quickly due to the cut
- Clean twist drills regularly to remove chip residue.
- Always pre-drill larger diameters, especially in combination with hard materials (e.g., stainless steel).
- Use the correct speed.
- Do not apply too much pressure when drilling; let the drill do the work. Precise drilling is only possible when the cutting edge, machine, and speed are all compatible.
Practical comparison: What really happens during drilling?
| Test material | Rolled drill | Ground drill |
|---|---|---|
| Structural steel (S235) | Clean hole, slight burr | Clean hole, hardly any reworking necessary |
| Stainless steel (VA) | Non-machinable, blunt | HSS-Co 5 drills provide precise drilling and good chip removal |
| Plexiglass | Risk of cracking, breakage | Smooth drill edge, no cracks |
| Aluminium | Easy to drill, chips stick | Low friction, clean cut |
Beginner's guide: How can I identify the twist drills in my toolbox?
| Feature | Rolled | Ground |
|---|---|---|
| Color | Dark gray to black | Metallic silver, shiny inside |
| Internal coil | Matt, slightly rough | Smooth, polished, often shiny |
| Transition shaft/spiral | Slightly round, soft | Sharp-edged, precisely milled |
| Labeling | Usually no type designation or simple type designation: HSS-R | Most accurate type specification: HSS-G |
Temperature behavior in comparison
Heat resistance is often underestimated when drilling—it is particularly important when working with metallic materials. Drilling generates temperatures of up to
- Rolled drills: Heat up and dull more quickly due to friction. Without cooling, they are only suitable for short drilling operations.
- Ground drills: Stay sharp significantly longer when used correctly – especially in combination with cobalt (e.g., HSS-Co 5) or coatings (TiN, TiAlN). Link to HSS-Co 5 and coatings blog article
Important: Cooling is worthwhile for both types of drills, but especially for ground drills when working with stainless steel and similar materials.
Conclusion
Ground or rolled – this difference determines the quality, durability, and efficiency of your work. While ground drills stand for precision and demanding materials, rolled drills stand for robustness and cost-effectiveness.
The right choice depends on your area of application. Those who often work with metal should invest in ground twist drills. They have optimal concentricity and create precise drill holes. Their disadvantage is that they break easily and are therefore mainly suitable for stationary drills.
For occasional users, rolled drills are the better choice. They are perfectly adequate for ordinary drilling with a hand drill. Although they are not as precise as ground drills, they are considerably more robust and cheaper.