I'm using Mach3 ***.056 and have been for some time. I'm building a Joe's EVO CNC and now I've found a new problem. I thought I had been through most of the glitches. I'm trying to make a plaque that I've made about 50 times before on my old Blacktoe CNC router.
For some unknown reason the Z axis is not cutting to the right depth when the g-code calls for a depth change. The code says to cut to 0.045 below zero but the tool (a 90 deg v-bit) barley scratches the surface of the wood. The Z DRO shows the depth change but for some reason the stepper is not moving to the right depth. I have re-calibrated the stepper so many time I've lost count. I use the auto calibrate and move Z down 4" to set the steps. When I recheck the movement of Z it is almost perfect. But this is not reflected when I try to run g-code.
Question: could this be noise in my system?   Or is there a setting I'm missing?  
I'm using a Chinese spindle and VFD which has been the source if most of my problems because of the RF noise. I have shielded wire on the spindle but I don't think the shield is grounded very well. So tomorrow I will do a better job of grounding the shield.

This morning I connected the shielding in the output wire from the VFD to the spindle.   
Looks like the shielding has to be grounded on these Chinese spindle-VFD. And some advice: NO ground wire from the spindle motor to ground.
The noise output from these Chinese spindle-VFD is significant.  Caused all kinds of problems while running G-Code even though the gantry would jog up & down the table smooth as silk.

The Z DRO shows the depth change but for some reason the stepper is not moving to the right depth.

Perhaps a mechanical problem with your machine (loose grub screw, slipping coupling, etc.) or an electrical problem (Z axis motor, motor driver, wiring connections, etc.).

Tweakie.

Hi Tweakie,
I'm sure my problems was noise coming from the spindle. I ran some g-code without any difficulty. Let's hope that this is the last of the glitches with this CNC router.