TABLE OF CONTENTS Series of tool motions programmed before the first element of the contour is machined is called tool approach or lead-in motion. When the tool approaches the contour, it can approach a face, diameter, chamfer or a taper, or a radius. A series of similar drawings shows the main features of a tool approach towards a part (not to scale for clarity). Note that the approach direction is only an example, and can originate from another point.
In most turning jobs, there will be a need to program at least one facing cut, to remove the front face stock. The tool should start well above the stock diameter by a clearance C of 2.5 mm (or 0.1 inches) per side or more, if necessary. Keep in mind that not all parts are perfectly round and the rotation increases the effective stock diameter. Using cutter radius offset for the face alone is nor necessary, but will do no harm if programmed correctly.
Example:
In this case, it is not necessary to include the G41 command, but there is no harm in doing so.
Any tool motion towards a diameter is the easiest to program and requires no special considerations. It is similar to the previous example, except for the cutting direction. For both external and internal cuts, the tool should have a suitable clearance from the part, along the Z-axis. Typical clearance C of 2.5 mm or (0.1...
