This is a great question since an angular start hole is a situation that commonly occurs in mold tooling lifter pocket or ejector pin details. As part of this process, a position for manual wire threading needs to be determined within the profile, and an M01 stop point should be created within the NC program at this point.  When processing with a tapered start hole, the angular start hole position needs to become part of the program so that it is included within the program cutter compensation (G41/G42) line.

If the angular start hole location is not part of the utter comp (G41/G42) movement, a machine alarm can occur. In the case of 4-Axis programs, cutter comp may not be activated properly if the U/V axes are not vertical, leading to improper size and location.  Depending on the output and options of the CAM systems, some manual editing of the program may be required. However, the overall changes will be minimal.

It is possible to create programs with angular start hole locations using “T” taper NC code or full 4-axis programs.  As part of all U/V axis machining, the taper data information (program plane, sub-plane, and Z-position) must be properly set and can be programmed using the G95 statement.

The images below show an example of a 15° angular hole in a workpiece with a height of 2.500 inches.  A tapered start hole is necessary because the top and bottom profiles do not intersect the Z-plane top View.  This example has been processed as a 4-Axis program, and the standard program NC code and modified NC code for the tapered start hole have been provided.