Chip control

Chip formation and chip evacuation is a critical issue in drilling. It depends on the workpiece material, choice of drillI/insert geometry, coolant pressure/volume, cutting data.

Chip jamming can cause radial movement of the drill and affect hole quality, drill life and reliability, or drill/insert breakages.

​	Thicker and stiffer chips​	​
Speed  ​	​	More open due to less friction​
​	Feed​	​

The chip formation is acceptable when chips can be evacuated from the drill without disturbance. The best way to identify this is to listen during drilling. A consistent sound means that chip evacuation is good, but an interrupted sound indicates chip jamming. Check feed force or power monitor. If there are irregularities, chip jamming can be the reason. Look at the chips. If they are long and bent, instead of curled, chip jamming has occurred. Look at the hole. If chip jamming has occurred, an uneven surface will be visible.

​

​	​	​
A hole with good chip evacuation.​	​	A hole affected by chip jamming.​

To avoid chip jamming:

• Make sure the right cutting data and drill/tip geometry is used
• Inspect chip form – adjust feed and speed 
• Check the cutting fluid flow and pressure
• Inspect the cutting edges. Chipping on the edge can cause long chips, while the chip is divided
• Check if machinability has changed due to new workpiece batch – adjust cutting data

Excellent, acceptable and unacceptable chips

Indexable insert drills

The central insert forms a conical chip that is easy to identify. The peripheral insert forms a chip similar to that formed by turning.

​Central strip		Peripheral chip​
Excellent​		Excellent​
​		​
Acceptable​		Acceptable​
​		​
Chip jamming​		Chip jamming​
​		​

Solid carbide drills

One chip is formed from the centre to the periphery of the edge.

​Excellent	​	Acceptable​	​
​	​	​	​
Chip jamming​	​
​
​	Start chip​ ​

Exchangeable-tip drills

Excellent

Acceptable

Unacceptable, risk for chip jamming