A broken drill bit can stop production, damage a workpiece and leave you with a difficult extraction job. When drilling thick steel plates, reducing breakage starts with matching the tool and cutting settings to the material, then keeping the workpiece stable and the hole clear of swarf.
This guide focuses on conventional twist drilling with an industrial pillar drill. Specialist carbide and deep-hole tools may require different procedures, so always follow the tooling manufacturer’s recommendations.
Why do drill bits break in steel?
Drill bit breakage usually involves one or more of these problems:
- Unsuitable speed or feed: Excessive cutting speed accelerates wear, while too much feed can overload the drill.
- Trapped swarf: Chips packed into the flutes can jam the tool.
- Movement or misalignment: Poor workholding, excessive run-out or an unstable setup can load the cutting edges unevenly.
- Worn or damaged tooling: Continuing with a blunt or chipped drill increases the risk of failure.
- Inadequate cutting fluid: Insufficient delivery can affect cooling, lubrication and chip evacuation.
Plate thickness alone does not explain the problem: hole diameter, depth, steel grade and tool design all matter.
1. Choose the right drill bit for the material and depth
Check the steel grade and condition before selecting your tooling. A drill suitable for mild steel may be unsuitable for hardened steel.
Choose a drill rated for the required hole depth, with enough flute length to evacuate chips. Use the shortest suitable tool to limit deflection, and inspect its cutting edges before starting. Replace or correctly resharpen worn tools instead of compensating with more pressure.
2. Set spindle speed to suit the drill diameter
There is no single correct RPM for drilling thick steel. Start with the tool manufacturer’s recommended cutting speed for the steel grade, drill material and coating.
For the same cutting speed, a larger drill diameter requires a lower RPM.
Plate thickness mainly changes the drilling depth and the challenge of getting chips and coolant in and out of the hole. Deeper holes may require adjusted settings, but simply reducing RPM is not a complete solution.
Maintain a controlled feed that allows the drill to cut. Excessive feed can overload it, while insufficient feed can increase wear.
3. Clear swarf before it packs into the flutes
As the hole deepens, chips have further to travel before they can escape.
For conventional twist drills, peck drilling may help: advance in controlled stages, then retract as recommended by the tool supplier to clear chips. The appropriate peck depth depends on the drill, material and coolant arrangement.
Peck drilling is not a universal requirement. Some through-coolant drills are designed to reach their rated depth without pecking. Follow the tool manufacturer’s recommended drilling procedure.
4. Deliver suitable cutting fluid to the cutting area
Use a cutting fluid suitable for the material and tooling, at the supplier’s recommended concentration where applicable. Check that the supply reaches the cutting area and that chips are not obstructing it.
An integrated coolant system is useful, but cannot compensate for worn tooling, unsuitable settings or blocked flutes. If cutting performance deteriorates, stop and investigate before continuing.
5. Secure the plate and check the setup
Clamp the plate securely using suitable workholding, and support large or heavy workpieces appropriately. Never rely on holding the plate by hand.
Check that the drill is correctly seated and that the table, vice and relevant machine adjustments are secure. Keep tool overhang to the minimum required.
Follow the machine’s guarding instructions. Stop the spindle before clearing accumulated swarf, and use a suitable brush or chip hook rather than your fingers.
6. Choose a pillar drill suited to the job
For regular steel drilling, consider drilling capacity, available spindle speeds, rigidity, feed control and coolant provision.
A geared head pillar drill can be a practical choice for demanding workshop use, particularly where larger drill diameters require operation at lower spindle speeds.
Select the machine around the hole sizes, materials and workload you need it to handle. Correct tooling and setup remain essential to achieving consistent results.
DIMAKIN pillar drills for steel fabrication
The DIMAKIN DP-3175-M and DIMAKIN DP-3810-A both feature gear-driven transmission, inverter-controlled speed adjustment and integrated coolant systems.
| Feature | DP-3175-M | DP-3810-A |
| Rated drilling capacity in steel | 32 mm | 40 mm |
| Feed | Manual | Manual or automatic |
| Low spindle-speed range | 65–540 RPM | 65–540 RPM |
| High spindle-speed range | 245–2,000 RPM | 245–2,000 RPM |
| Spindle taper | MT3 | MT4 |
Drilling capacity refers to hole diameter, not maximum plate thickness. Suitability for a particular job also depends on the steel grade, tooling, hole depth and setup.
Looking for a pillar drill for your workshop? Explore the DIMAKIN industrial pillar drill range or contact our team for help choosing the right machine for your work.
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