Are more flutes always better? - Indexable.

Categories: Knowledgebase

Theoretically, more teeth with the same diameter and feed per tooth will yield a higher performance by increasing the inches per minute, but there are physical limitations that will sometimes negate this advantage. More teeth means there is a shorter time between tooth impacts for the tool to deflect and rebound. To make up for this shorter time between teeth you have to decrease the force deflecting the tool and you do that by reducing either the depth of cut, the width of cut or a combination of both. you can see this in a stability lobe diagram comparison:

The 8 tooth face mill is in red and the 4 tooth face mill is in blue. You can cut far deeper with the 4 tooth.

Here is the 8 tooth face mill. We are depth of cut limited by the stability of the cutter and the power limit. We can achieve  a metal removal rate of 16.16 cubic inches per minute. 

Here is the 4 tooth face mill. We can cut twice as deep which overcomes the lower feed rate with half as many teeth. We can achieve a metal removal rate of 20.24 cubic inches per minute, a 25.2% improvement. 

There is another thing that must be considered with indexable face mills. More teeth require more power. 

Here is the 8 tooth face mill. The pink line is the torque and power curve of the machine's spindle. Some of the stable speeds and cutting depths will exceed to power limit of the spindle.

Here is the 4 tooth face mill and you can cut deeper as well as faster before reaching the power limit.