21. TWO–PATH CONTROL
When a thin workpiece is to be machined as shown below, a precision
machining can be achieved by machining each side of the workpiece with
a tool simultaneously;this function can prevent the workpiece from
warpage that can result when only one side is machined at a time. When
both sides are machined at the same time, the movement of one tool must
be in phase with that of the other tool. Otherwise, the workpiece can
vibrate, resulting in poor machining. With this function, the movement
of one tool post can be easily synchronized with that of the other tool post.
Fig. 21.4(a) Balance cut
When G68 is specified in the programs for both tool post 1 and tool post
2, the pulse distribution of tool post 1 is synchronized with that of tool
post 2 to start balance cutting. Thus the two tool posts can move exactly
at the same time to allow balance cutting.
G code Meaning
G68 Balance cut mode
G69 Balance cut mode cancel
In the balance cut mode, balance cutting is performed only when a move
command is specified for both tool posts. Balance cutting is performed
even when different axes are specified for each tool post or an offset move
command is specified. G68 or G69 must be specified in a single block.
(Otherwise, a P/S alarm (No. 163) is raised. When G68 or G69 is
specified with one tool post, the tool post does not move until the
execution for the other tool post proceeds to G68 or G69. And if cutting
is specified with one tool post in the balance cut mode, the tool post does
not move until the execution of or the other tool post proceeds to a cutting
Balance cut only starts cutting feed on both tool posts at the
same time; it does not maintain synchronization thereafter.
To synchronize all the movements of both tool posts, the
setting for both tool posts, such as the travel distance and
feedrate, must be the same.