Engraving small font - the bit digs deeper and deeper as the job goes on. 6040z

[Clive S]

Here is a YouTube video of the issue, and I have attached a photo.

As Rob suggests I think you have a problem with the bearing holding the screw in position the motor should certainly not be doing that job. It will further damage your machine without sorting this problem out.
Take the motor off and see if you can check for end float in the screw