What is “run-out” in handheld drills?

When referring to handheld drills or drilling units, run-out (or runout) occurs when the drill bit does not circulate around its own axle in an absolute straight line (picture 1). It is


Picture 1

very difficult to get rid of all run-out, but it is important to minimize it as the end quality of the hole is ultimately affected. In other words – the final hole will not be 100% round if there is too much run-out.


There are many factors affecting the amount of run-out:

  • The drill bit
  • The chuck or collet
  • The operator
  • The tool

How to ensure run-out is reduced

When tightening a tool chuck, use all 3 positions to tighten with an even torque, using the chuck key. This will create equal pressure from all three jaws in the chuck holding the drill bit and reduce run-out (picture 2). Check the inside of the chuck jaws for damage or wear. If the jaws are worn, this could create excessive run out. A chuck is a consumable and should be changed from time to time, depending on usage.

Three Jaws.png

Picture 2

When run-out occurs…

It is helpful to know the statistics regarding reasons for run-out, so that you can assess and anticipate why this may be happening. Most likely – 90% of the time – the drill bit in use is damaged or corrupt. 9% of the time run-out is experienced, the tool’s chuck teeth are damaged or worn out. Only 1% of the time is the actual tool damaged or not assembled correctly (picture 3).


Picture 3