I am trying to cut a 3d carving on mach 4 after creating the g code in Aspire but, when I run the code it dose not hold the z axis it moves to different heights. It cuts the 3d image at different heights leaving layers like a pyramid in the image. Any suggestions on how to fix?  I have a 4x8 Avid cnc pro version .

Sounds like a z axis stepper problem. You may need to lower the acceleration and or the max velocity. Can you jog the Zaxis up and down?

Stab in the dark here with little information but does the 3d image render correct in Aspire or stepped like the output.  If correct in Aspire did you use the same bit as in Aspire. (ball nose in Aspire and end mill in reality.  Did you output both a 3d roughing toolpath and a finish toolpath or just the roughing toolpath?

HTH

RT