It should be doing that already. Your program should call the next tool as the current tool starts running.
Here's a sample of one of my prestage programs.
( OPERATION: 3 DRILL )
N37 ( DRILL 2-56 )
N38 G91 G28 Z0
N39 G91 G28 Y0
N40 G90 G00 G52 X-40.
N41 M06(T6: 5/64 DRILL)
(MAX-DEPTH | Z-.5)
N42(OP ID: 3)
N43 M03 S6500
N44 G00 G90 G58 X.5395 Y.115 A0.
N45 G43 H6 Z1. T7
/ N46 M08
N47 Z.1
N48 G98 G83 X.5395 Y.115 Z-.5 R.1 I.1563 J.0391 K.0391 F10.
Note line 41. Tool 6 is current tool running, called with ONLY an M06.
On line 45, (H6 running), calls the next tool with ONLY the T7. This will cause T7 to be rotated to pocket for next tool change.
Matt
San Diego, Ca
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(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)