Bit not touching Bit Plate

[fwharris]

Give the Z bearings and rails a good cleaning with air and some WD-40 on a rag and then a good lube.

[Digitalwoodshop]

Look especially at the lower keyboard side bearing as it gets the splatter from cutting. Mark it with a marker and be sure it is turning not sliding.

Look close at the Z Belt and the cogs, they fill with wood dirt and cause the "Z" to think it bumped into the bit plate when it did not. Remember during the bit checks the computer looks at Z motor current and when it raises it thinks it bumped into the bit plate. So DIRT can confuse the computer.

ALSO look at the Flex Drive, as it can SCRAPE the black cover slot causing a false Z position. Usually a worn Truck "Top Hat" where the bearing of the top hat cuts or wears a slot making the Flex Drive Droop.... Turning the Top Hat 180 degrees will help the droop.

Get a tooth brush size wire brush and scrub the 2 vertical Z Rails too... a LUMP of dirt acts as a Bump and can give you a false Z data...

And like posted above... The Z Motor Encoder can be DIRTY or even the clear disk slipping. But since you can "Help" and push the Z Down and it carves normal this is not likey or a bad FFC Cable either... It's a Mechanical Thing...

Binding due to DIRT causing a false Z Position.

And I see you joined in 2008..... This would be classic symptoms of the old 18 pin FFC Cable System... Do you have the old 18 or the newer 14 pin? The thinner 18 pin wires offered less current or PUSH... It's like a AAA Battery and a "D" Cell Battery... One has less "Push"....

Sorry I did not chime in sooner...Jury Duty yesterday.