ok long story short I've been using mach 3 since July on a new cnc router without issue until a few weeks ago when it has started randomly plunging the Z axis through work piece into the table breaking bits and trashing the sheet . i have ran it for months 8-10 hrs a day without issue till just recently, running the same exact programs from before the issue started. i havent changed a single setting other than the rapid speeds between cuts . also if it makes a difference i am doing all my designing and g-code generation with V-carve9.0
 any help would be greatly appreciated ......this is costing me a fortune in bits and wood!

Hi,
I would guess that it is missing steps and/or being affected by electrical noise.

Electrical noise can and often does come and go, usually as a result of some very subtle change, maybe a wire shifting or similar.

Craig

  it has started randomly plunging the Z axis through work piece into the table breaking bits and trashing the sheet . 

Another possibility is mechanical slippage in the Z axis drive components.
The slide mechanism can get gummy over time requiring more effort to raise the motor assembly. This along with an increase in rapid speed and/or acceleration can overpower the pulley or shaft coupling set-screws. Might pay to double check the mechanical aspects as well.
Russ

Ok after  a lengthy phone conversation with the company who sold me the machine and some switching of cables we have apparently  rectified the situation and have ran two solid days without a glitch ! Thank you for the info