When the finished product requires a 90° corner then a shoulder mill needs to be selected. For general milling or planing of open surfaces is to be carried out then a typical plain type mill should be selected. This is because the chips generated are thinner and therefore the load on the cutting edge is reduced offering longer tool life. For plain milling cutters there are a number of corner angles available. Typical corner angles for plain mills include 15° , 25° , 30° and 45° . For each corner angle stated the machining properties vary.
0° corner angle
When milling with a 0° corner angle, the back force works in the minus direction (see image to the right). Therefore, if the workpiece clamping is insufficient then the workpiece will be pulled upwards. This can result in vibrations and consequently a poor surface finish.
15° corner angle
When milling with a 15° corner angle the back force works in the positive direction (see image to the right). Due to the 15° angle though the amount of back force is not so high as when compared with a 45° corner angle. The 15° corner angle is therefore suitable for workpiece materials and applications that lack rigidity.
45° corner angle
In comparison with the 0° and 15° corner angles a larger back force is generated (see image to the right). This back force works in the positive direction. When milling with a 45° cutter the workpiece is effectively being pushed downwards. Therefore this type of corner angle is not suitable for workpieces that have thin walled sections, as they can bend under the force exerted and the required machining accuracy may not be achieved.
The 45° corner angle is however suitable for milling cast iron as it prevents chipping of the workpiece.
Dealing with clamping/cutter interference
Depending on the workpiece geometry and the clamping method used, there maybe cases where a plain milling cutter cannot be used because of interference between the cutter body and the component clamping. In such circumstances there is no choice but to change the cutter to a shoulder mill type cutter (0° corner angle).