hi friends...

In our machine threading cycle is not running properly.
The cycle was running okay few days back but now whenever we run threading cycle G92, G76 the machine starts the cycle normaly.
After one thread cut when it goes for the second cut to increase the depth it changes the thread start point and when it goes for third one it again changes the thread start and this goes on with each cut and the result is rough turning instead of threading.
Whereas the pitch remains the same in every thread but somehow it changes the start point of the cut.
Sometimes in the center of first thread pitch and every time it varies in multiple thread cutting and we already have tried G92 but the condition remains the same.
We have checked the repeat-ability of machine.
we have checked the backlash of machine.
The spindle RPM remains constant with +/- 1.
We have checked threading parameters of the machine.

Every thing seams to be okay but still machine is doing rough turning instead of thread cycle
Please help and thanks in advance...