End milling

For helical flutes, the cutting resistance gradually builds on a workpiece from the end cutting edge and thereby changes slightly. Meanwhile, with a straight flute, the cutting resistance is simultaneously placed on the whole cutting edge length and therefore changes significantly throughout the cutting cycle. The image below shows an example.

The back force of cutting resistance is applied in an end mill's axial direction. As the helix angle increases, cutting resistance from the component in an axial direction increases the back force. The image below shows a measured example. When machining thin parts and workpieces that lack rigidity with an end mill with a high helix angle, care should be taken because bending of the workpiece and vibration can occur.

The figure below shows the effects on deflection when using various helix angled end mills to machine a slot. It can be seen that the largest amount of deflection occurs with a certain helix angle. As the helix angle increases the amount of force acting towards the up cut side of the slot increases.

Surface roughness improves with a higher helix angle. This is because increased sharpness reduces cutting resistance.

The helix angle also affects tool life. As the helix angle increases, the contact length of the cutting edge also increases, the result of which leads to a decrease in tool wear. However, as shown in the graph below, when a helix angle increases over a certain limit, the cutting edge strength decreases and tool life shortens.