Random bed retractions causing stringing? UM3 & Cura 4.1.0

[kmil81 3]

I'm the proud new owner of an Ultimaker 3. It is living up to the promise of being user friendly and reliable.  This is my first experience with both Ultimaker and Cura.

 

I have noticed one strange thing in some of my test prints.  When the printer is traversing open space (from a point where it printed, over an area where there is no print, headed toward its next extrusion area), sometimes it heads straight over at the same height (in which case there is no stringing occurring) however, sometimes it quickly lowers and then raises back up (total travel is sub-second) the print bed leaving a string like you would expect to see at the end of a print.  It feels random when it does it (as in it's not always at the end of a layer). The end of a layer does the very slight lowing of the platform to get to the next layer (as I would expect it to) rather than this more significant lower and then raise behavior.

 

I've found the setting "Enable retraction" option in the Material section but this refers to retracting the filament when traveling over non-printed areas, not lowering the bed. I'm relatively new to 3D printing so reading g-code to figure out why it does this is not within my current capabilities.

 

Does anyone know if there is a setting for this or a way to get it to stop this behavior?

 

Thank you all for your help!

[kmil81 3]

Forgot to mention, I'm printing using the silver Ultimaker PLA that came with the UM3.  Attached is an example of one of my test prints. Most of the gaps have no stringing. It's only occurring when it does the bed drop and then raise behavior.

[gr5 2,265]

It's called "hop".  Search for "hop" in the settings and you will see "z hop when retracted".  You need to uncheck that for UM printers.  That is a useful feature for delta printers.  I'm told.

 

It only hops if it's a retraction move.  There are other settings that decide which moves are retraction or non-retraction moves.  If you look at the part in preview mode and check the "show moves" box you will see one type is light blue and the other dark blue.

[kmil81 3]

Thank you so much for your help!

 

I see that the settings tooltip mentions that this helps the printer avoid hitting the print when traveling. It sounds from your reply that this is not a risk on Ultimaker printers. Is that accurate? Would there ever be a case when I would need this to be on with the UM3 (dual filament prints perhaps)?

[johnse 31]

The UM3 moves print core 2 up and down so that only the core currently being used is at the level of the layer being printed. When core 1 is printing, core 2 is retracted. When core 2 is printing it is lower than core 1, effectively retracting core 1.

 

so, no, dual material printing doesn’t need the z-hop.