CNC lathe Ecoca EL-6120 with Meldas 500 chamber programmation

[Tom1994]

Hello,

I have an old CNC lathe ECOCA EL6120, with Mitsubishi meldas 500 program environment.
I am having troubles with the programmation of the groove for the workpiece in attachment.
I don't use CAD/ CAM or a postprocessor.
Below is the program I have made.
I am using a using a round grooving tool R1.5mm.
The machine only does one roughing pas and then immediatly does the final pass.
Probably I am not allowed to use the G71 roughing cycle, because it can't do an undercut?
What is the correct way to program the roughing phase of this chamber?

N10 G00 G40 G54 G96 X300 Z300 ;
N20 G92 S300 ;
N30 M00;
N40 T0606 ;
N50 G00 X40 Z-10 M03 S150 ;
N60 G42 ;
N70 G71 U1. R1 ;
N80 G71 P80 Q140 U0.5 W0.3 F0.2;
N90 G01 X30 Z-7.76 ;
N100 G03 X25.96 Z-10.93 R3.5 ;
N110 G01 X23.46 Z-11.51 ;
N120 G02 X20 Z- 14.23 R3 ;
N130 G01 Z-15.77;
N140 G02 X23.46 Z-18.49 R3;
N150 G01 X25.96 Z-19.07
N160 G03 X30 Z-22.24 R3.5
N170 G01 X 35 ;
N180 G00 G40 X300 Z300 M05 ;
N190 M00;
N200 T0606 S150 M03;
N210 G00 X40 Z-10 ;
N230 G42;
N220 G70 P90 Q170 F0.2;
N230 G00 G40 X300 Z300 M05
N240 M30;


Thank you in advance.