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 absolutely straight line.
It is 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, including:
- 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.
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).