Denford Software & Machines

Our 2600 Pro has done this a couple of times in the last two weeks while cutting CO2 cars - running along fine and then steps down about 20 mm like it lost its zero on the z axis. I suspected trash on the lead screw or ways was making the stepper lose its place so I cleaned these thoroughly and lubed them. All was well for a week or so until it just did it again. The machine is cleaned well between cuts and I wouldn't think it would need to be lubed that often. Is there another issue that could cause this?

When you say you lubed the lead screw & ways I presume you used silicone spray? It does take roughly 4 hours to dry so you need to leave it overnight otherwise it just wears it off.
It could also be dust in the Z axis motor brake which you can strip down but check the silicone first.