34
3
）
Considering what kind of loop hole processing way, as introduced in below G73
～
G89 circulation
processing instruction.
13.2 The Main Instruction Affecting the Machining Cycle
13.2.1 Coordinate Programming Instructions (G90/G91)
In the fixed cycle instruction, the specified data R and Z are relate to the pattern of G90 andG91. Coordinate
calculation method of G90 and G91 are shown in Fig. 13-2. R and Z should be the end of the coordinates in usage
of G90. R is distance between initial point to R point and Z is distance between flat bottom of the hole to R point
in usage of G91.
Fig. 13-2
13.2.2 Return Plane Selection (G98
，
G99)
Return plane is decided byG98 or G99. If the instruction G98 since the procedures section, cutting tool will
return to the initial plane, if the instruction G99 is the plane to return to the "R", as it shown in Fig. 13-3.
Usually when processing a set of identical hole, processing after the first hole with G99 returns to the R, after
processing the last hole with G98 returns to the initial plane.
Generally, if processing hole in a flat plane, you can use the G99 instruction, because in G99 mode is return
to R point to the next hole positioning, and general programming R point is very close to the surface so that we
can shorten the processing time. But if the workpiece surface is higher than the processing hole convex or
reinforcement, when using the G99 collision is very likely to make the cutting tool and workpiece. At this time,
you should use G98, return to the initial point Z axis and then go to the next hole positioning, so it is safe.
