I'm putting this problem in Art Soft because I don't know where the problem originates from. I'm using the center of the project as the center point and the carving starts out well but then the spindle shifts about 4 inches off center and continues. If I allow it to run its course it does the rest of the carving 4 inches off center. I cannot tell where the problem is. I'm using mach4 ver. 4.2.0.3461 the machine is home built and I have been using it for about 4 years.

Thank you in advance

Are you using stepper motors?

Yes. The off center is in the Y axis.

It wounds to me like either the motor is stalling or something is slipping.
Try slowing the move speed and make sure the screw or gear that moves it is tight.

Oh dear. Before I read your post I decided to recenter the carving and run the rough cut again, which I did and it cut as it should. When it finished I changed the bit and ran the finishing tool path and it started out well then gradually began cutting deeper and deeper until it cut all the way through the material. I just checked all the ball screws and they are tight. I'll try slowing the motor speeds.