Z hop is usefull when you notice that the nozzle leaves marks on the surface of the model when it moves over the last printed layer. This can be seen on the upper closing faces of the model, and is due to the movement of the extruder, which for some reason crawls on the print.
We can be in the presence of overextrusion, and the deposit of more plastic than necessary turns into an accumulation, which the printer can not read in any way and then goes through it. In this case we can refer to the problem already dealt with in this POST, and solve it at its root.
The same problem can occur under normal conditions, however, due to the paths that the slicer decides for the nozzle.
In this case the slicer itself (any slicer program) offers us the solution to unsightly scratches, through the option Z-hop.
If we see the Z-hop option in action, we will immediately realize that it is a real jump, from one point to another of the press.
This leap avoids the formation of scars on our model but if it is not set up properly it can bring us more problems than solutions.
We immediately realize that in the vast majority of printers the X and Y axes can move much faster than the Z axis. This means that when facing a “jump” the printer will make 3 different movements: Z up, movement of X/Y and Z down. Due to the slow movement of the Z-axis, the two ascent and descent times will take up most of the time.
Dead time in 3D printing is undoubtedly the home of stringing, and we will most likely encounter this problem.
To avoid it you can increase a little the parameters of retraction, following the advice of the article on stringing, but if we can not correct the shooting maybe we will have to opt for the lesser evil and a couple of marks on the surface of the model will not seem to us then something so serious.