What is a core drill?
Whether on the building site, in metal construction or for renovations - core drills have become an integral part of modern trade. But when does it really make sense to use them? What are the differences to twist drills and which materials can be processed?
Core drill explained simply
A core drill is used when larger and precise holes are required in metal - for example in steel construction or assembly work. The main advantage of core drilling is that it eliminates the need to pre-drill with smaller drills. In their application, core drills are comparable to hole saws and are used to produce larger drill diameters precisely and efficiently.
In contrast to twist drills core drills only remove the edge of the drill hole. The material that is removed by the core drill is called the drill core and remains undamaged, which reduces material removal.
The reduced material removal results in lower forces and less heat generation, especially with larger diameters and demanding materials.
Structure of a core drill
1. Cutting
The cutting edges can vary depending on the model and application. Our core drills are made of HSS steel (available either coated or with a CO-5 content) There is also a version with carbide cutting edges.
For core drills with carbide cutting edges, the cutting edges are soldered onto the HSS body in order to cut powerfully through the material.
For core drills with HSS cutting edges, the cutting edges and the body are ground in a single production step.
In both cases, the cutting edges are exposed and are positioned like teeth in the cutting direction. This is the tooth geometry of the tips, which is optimised for the application.
2. Flutes
The bodies of core drills are ground using CBN (cubic boron nitride) grinding wheels. This precise manufacturing process ensures uniform geometry and promotes smooth operation and efficient chip removal. Due to the high hardness of the CBN grinding wheels, the material structure is cut through during the grinding process, resulting in cutting edges that are more dimensionally stable and sharper.
The U-shaped flute ensures optimal chip removal. This reduces the thermal load on the core drill, as the heat generated during machining is largely carried away with the chips.
Core drills with carbide cutting edges have a significantly shorter flute than conventional core drills.
3. Shaft / holder
Core drills have a shank that is clamped into the machine via a holder. There are three different shanks for the core drills in our range: Weldon shank, Quick-IN shank or shank with threaded holder.
The machine must of course have the appropriate holder.
4. Ejector pin
The ejector pin is preloaded with a spring and pushes the drill core out of the drill hole.
It is also used to centre on the centre punched drilling point when positioning.
There are ejector pins for HSS, carbide with Quick IN shank or HSS with Weldon shank.
5. Material - high-speed steel without and with cobalt
Core drills are made from high-speed steel (HSS). HSS has a cobalt content of 0.5 to
1.5 %. HSS-Co 5 core drills, on the other hand, contain 5 % cobalt.
Cobalt is largely responsible for the hardness of the material. The higher the cobalt content, the harder the tool.
However, you cannot tell from looking at a drill whether it is made of HSS or HSS-Co 5.
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Drilling time comparison: core drill vs. twist drill
We carried out a drilling comparison between HSS twist drills and HSS core drills, which clearly showed how enormous the time savings are, especially with large diameters.
Because core drills remove material from only a ring-shaped section rather than the entire drill diameter like twist drills, they work many times faster. Pre-drilling and reaming are no longer necessary.
The graph clearly shows that core drills remove material from a hole up to 7 times faster than twist drills. The lower energy requirements and reduced wear during core drilling also result in a long service life.
With twist drills, the entire drill diameter must be cut. This requires a high amount of force and high drive power. For larger diameters, it is also often necessary to pre-drill with smaller diameters, which further extends the work process.
For safe and material-compatible use, the speed guide values of the manufacturer should always be observed when core drilling.
Where are core drills used?
Typical areas of application for core drills are
- Steel construction and metalworking: e.g. beams
- Electrical and plumbing installations: e.g. cable ducts through metal
- Industry and mechanical engineering: e.g. series drilling, assembly work
- Assembly and maintenance: e.g. in plant construction or maintenance
Which materials can be processed with a core drill?
Depending on the type of tool steel (HSS, coated HSS, HSS-Co 5, or carbide), the following materials can be machined:
- Unalloyed and alloyed steels up to 1,100 N/mm²
- Mild steel, stainless steel and aluminium
- Hot and cold work steels
- Tempered and case-hardened steels
- Composite materials and sandwich panels
- Difficult-to-machine materials
Conclusion
Core drills are the ideal solution for creating larger drill holes in metal with precision, cost-effectiveness, and time efficiency. Thanks to their annular cutting principle, they minimize material removal and enable stable drilling processes with less strain on both the machine and the tool.
Those familiar with how core drills work and their areas of application can use them effectively to efficiently perform even complex drilling tasks in steel construction, industry, or trade.
FAQs: Frequently asked questions about the core drill:
The main difference lies in the machining principle:
- Core drill: cuts only the edge of the hole → faster process, less material removal, cost-effective
- Twist drill: cuts the entire diameter → requires more force, more time-consuming compared to core drilling
Core drills are therefore particularly efficient for large diameters and serial drilling in metal.
A core drill is particularly worthwhile for:
- Large drilling diameters
- Series drilling
- Applications in steel construction
- Mobile applications with magnetic drilling machines
Here, machining time, energy consumption and tool wear can be significantly reduced.
Typical machines for core drills are magnetic drilling machines and stationary drilling machines.
A suitable holder (such as Weldon or Quick-IN) and a stable guide are crucial for precise drilling.
The ejector pin has two main tasks:
- Centring the core drill during positioning
- Ejecting the drill core after breakthrough
Without a functioning ejector pin, blockages or incomplete core ejection can occur.