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8 reasons why drills break

July 23, 2020

Basically, drilling holes does not seem to be witchcraft. Nevertheless, especially when drilling into hard workpieces, it can happen that the drill breaks and in the worst case gets stuck. Find out in this article how this may happen and how you can prevent the drill from breaking.

There are different twist drills designed for different applications. But even the right twist drill for the intended application can break if used incorrectly. This can have different reasons which we have summarized below.

1. Using the wrong drill for the material to be drilled

The absolute basic is the selection of the right drill for the given application. If you use the wrong drill, you can adjust the other factors as much as you like, the drill will still break. We have compiled an overview of which tool steels are suitable for which applications.

Tool Steel Material/Application
High Speed Steel (HSS) Structural steel
High Speed Steel with cobalt content (HSSE-Co5, HSSE-Co8) Structural steel, Stainless steel
Solid tungsten carbide (TC) and HSSE-Co8 Structural steel, Stainless steel, High strength steels

The table is only a rough guide. For example, some HSS drills with coating can also be used in stainless steel. (You can read more about tool steels in our article High Speed Steel: From which steel are drills made of.)

Besides the tool steel, the length of the twist drill also influences the stability. The longer the twist drill is, the higher the risk that it will break. So only use a long drill when you are drilling into deep material.

Solution: Choose the right drill for the given application.

2. Workpiece and drill were not clamped firmly enough

If the workpiece or drill is not properly clamped during the drilling process, additional movements will occur, which can lead to breakage.

Solution: Fasten the workpiece well and clamp the drill firmly.

3. Poor chip removal

The grooved profile serves as a channel system for receiving and removing the chips. The wider the groove profile, the better the chip removal. If the chip removal is poor, the drill may jam and break off.

Poor chip removal also means increased heat generation, which in turn can lead to annealing and ultimately to drill breakage.

Solution: Use a coolant and lubricant and remove the chip by repeatedly moving the drill out of the workpiece.

4. Cutting speed and feed rate set incorrectly

If you are using a pillar drill, make sure that you select the correct speed and feed rate, otherwise the drill may break.

Solution: Check the cutting speed table and adjust speed and feed rate accordingly.

5. Poor quality of the drill

The twist drill may break if the drill is already worn out, has a manufacturing defect, is made of poor quality tool steel or is poorly sharpened.

Solution: Choose the right drill for the given application.

6. Small / large diameter of the twist drill

The twist drills are very sensitive for very small diameters. You could easily break them with your fingers.

Solution: For small diameters, make sure that you do not push hard.

For large diameters of e.g. 16 mm you should definitely pre-drill with two or three smaller twist drills. Drilling directly into solid material puts a strain on the drill and can lead to breakage.

Solution: Pre-drill the hole and repeatedly move the drill out of the workpiece (chip removal).

7. No cooling

As already indicated, very high temperatures occur during drilling. If you drill too long in one piece without pausing and letting the drill cool down a bit, it will get hot and break.

Solution: Cool with coolants and lubricants, remove the chip by repeatedly moving the drill out of the workpiece.

8. Using the drill in a handheld drill instead of a pillar drill

Some drills are only suitable for use in pillar drills as you have maximum control over feed and cutting speed. You can also guide the drill cleanly.

The harder the material of a drill is, the more brittle and susceptible it is to fracture. Solid carbide drills are very hard and should be used with pillar drills.

Solution: Choose the right drilling machine.

Conclusion and summary

Twist drills are designed for various applications. Depending on whether you want to drill in structural steel or high-strength steel, you must select the appropriate drill. If you do not do this, the drill may break.

We list eight reasons why drills can break:

  1. Using the wrong drill for the material to be drilled
  2. Workpiece and drill were not clamped firmly enough
  3. Poor chip removal
  4. Cutting speed and feed rate set incorrectly
  5. Poor quality of the drill
  6. Small / large diameter of the twist drill
  7. No cooling
  8. Using the drill in a handheld drill instead of a pillar drill

If you pay attention to the issues, your drills should be undamaged and remain with you for a long time.

Basically you should also follow the following points when drilling:

  1. use twist drills that hasn't already been used for other steels
  2. do not wear protective gloves
  3. put on protective goggles

Are you looking for the right twist drill for your application, then our product filter can certainly help you.

If you have any questions or if you want us to help you choose the right drill, you can of course contact us.

You can find our twist drills here Products > Twist drills.

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