Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 610)

Using Hemisphere Milling Cycles
Chapter 24
24-4
Prior to each plunge, the control computes a delta rough cut thickness, D’,
and a delta plunge depth, L’. These computations are based on the cusp
height (L parameter) and the hemisphere radius (R parameter) programmed
in the G88.5 block, and the tool radius programmed prior to the G88.5
block.
With the axis positioned at the plunge-position, a plunge along the Z axis,
of depth L’is performed. This plunge takes place at the plunge feedrate
specified by the E parameter.
After the plunge operation, the control performs a single-axis rough cut
outwards towards the left on the -X axis of the hemisphere. The width of
the first roughing cut is equal to the programmed rough cut thickness, D,
divided by two then multiplied by 95% ((D/2) x (.95)). The control then
moves the tool in a 360 degree circular path around the plunge-position.
After completing a 360 degree circular path, the control makes another
single-axis rough cut outwards along the -X axis by the rough cut
thickness, D. Another 360 degree circular path is cut that ends at the -X
axis. This process is repeated until the side of concave hemisphere, less
the finish allowance H, is reached.
Important: The thickness of the last rough cut is D’not the programmed
D parameter.
The tool is then raised by the clearance amount (AMP selectable, refer to
system installers literature) and moved at rapid feedrate back to the
plunge-position. This completes machining of one L level.
If the programmed Z depth of the pocket has not been reached, another
plunge takes place along the Z axis to the next L level. This level is then
machined as described in the previous paragraphs. This process is repeated
until the programmed Z depth is reached, at which time the tool is moved
at rapid feedrate along the Z axis back to the initial Z level. The tool is
then moved at rapid feedrate along the X and Y axes to its pre-cycle
position.