Vertical wall surface accuracy
Vertical wall surface accuracy (surface roughness of a vertical face) when shoulder milling is greatly influenced by the cutting edge geometry.
Theoretically, if the axial rake angle of a face milling cutter is 0, a true vertical surface will be produced. However, axial rake angles other than 0 are used in most cases to improve sharpness and to reduce the impact generated when entering the workpiece. In this case a vertical wall will not be produced.
- The reason for this is explained in
the animation to the right.
When fitting several inserts on a face mill cutter, there is some difference in the height setting of each insert. This difference is generally termed as run-out accuracy. This can heavily influence tool life and the surface roughness.
If the run-out is too large, then the surface finish will be poor and vibration and chipping of the inserts will occur. Additionally, inserts that protrude too much in relation to the others will do more work than other inserts and the wear development on those inserts will quicken.
The first image shows the relationship between the wiper runout setting and the surface finish. A standard wiper width is 1.4mm. If the wiper edge is set exactly parallel to the base of the face mill cutter, then theoretically, the surface roughness should be maintained even if there is some cutting edge run-out. However actually, there are problems such as irregularity due to run-out, wiper edges set inclined, poor combination of the accuracy of the cutter body and parts, welding on the cutting edges and vibration. Therefore, it is unavoidable to have some deterioration of the surface finish to some degree. Consequently, a wiper insert and a cutter specially designed for finishing operations are often necessary. For example, some cutters for finishing aluminium have an adjustable run-out system. By turning an adjustable screw shown in the second image.
Another type of face mill cutter is called a cutting edge height adjustment type (third image). They have only one insert location face on the cutter body, allowing the insert to be fitted in an optimal position by using a setting fixture.