Why are there some holes and some shallow holes in the woodworking engraving machine?
The Z axis alignment is not calibrated when setting the tool.
Engraving machine nose loose. For example: the screw is not fixed firmly, the knife chuck does not grip the processing knife.
The engraving machine is unstable. Will cause hole depth, a little deep, a little shallow (long engraving machine, easy to appear with drilling bag)
