Adtech ADTECH9 Series Programming Manual page 69

ADTECH9 Series CNC Programming Manual
Six Steps of Hole Processing Fixed Cycle
The instructions that have influence on the execution of hole processing fixed cycle instruction include
G90/G91 and G98/G99. Fig. 10.2 shows the effect of G90/G91 on hole processing fixed cycle instruction.
Effect of G90/G91 on Hole Processing
G98/G99 determines fixed cycle returns to point R or the start point after hole processing; in G98 mode, Z axis
returns to the start point after hole processing; in G99 mode, it returns to point R.
Generally, if the holes being processed are on a flat plane, we can use G99 instruction, because it will position
next hole after returning to point R in G99 mode; in general programming, point R is close to workpiece
surface, it will shorten part processing time; but if the workpiece surface has convex platform or tendon, the
tool and workpiece may collide if G99 is used; at this moment, G98 should be used to return Z axis to the start
point and then position next hole to ensure the safety. See the figure below.