Frage z axis and just digs in

Starting to get incredibly frustrated with my stepcraft!! For no reason it loses steps on the z axis and just digs in. Messes up the whole piece and cuts too deep that you can't even us the other side of the wood.

After I hit the emergency stop I moved the z axis up and down at speed and it was as smooth as you like!

Anyone else had this problem?

Did you check to see if there is looseness in the Z or X axes rollers?

Richard,

If the Z and X axis move smooth after an emergency stop it looks more like a software problem rather than a hardware issue. But checking the set screws never can do any harm.
Do you have an other CNC controlling program like WinPC-NC (starter or else) so you can check if that one is working well?
second check the post-processor file or use a different one to see if there are miscalculations in the g-code.

good luck and keep positive the Steppie is a fine HOBBY machine so be gentle.