Open seam in test print

[Mechatron127 0]

Hi all,

 

Today is calibration day over here!

 

I have calibrated my dual extruder to 415 steps/mm.

 

Now with flow set to 85% and horizontal expansion set to 0.05mm the 20x20x20mm test cubes come out pretty decent.

 

 

The wall thickness varies from 0,39 to 0,4mm and the X- and Y-width is between 19,94 and 20,01mm.

 

The print surface even looks decent also.

 

I have one reoccuring issue, you can see on the bottom right of the cube there is no connection between the bottom layers and the wall. 

There is a small string of filament where the non adhering slit starts, I have watched it using a magnifying glass, the string is not formed on the initial layer so I think it is the material that should have been where the slit is.

 

What could case this? (I have replaced the PTFE tube and 0,4mm nozzle today with new ones.)

 

KR,

 

Leo

 

PS: Is the flow percentage used to affect the E-calibration like X% times E-steps?

 

 

Edited April 3 by Mechatron127

[GregValiant 697]

The advantage to single wall (or double wall) calibration cubes is that you can really dial in your printer to produce spot-on single wall (or double wall) calibration cubes.

The disadvantage is that when printing anything else, it doesn't really work.

If you have your E-steps dialed in then you are done.  No further Flow calibration is necessary or required.

 

It's easy to calculate the volume of an extrusion.  L x W x H.  If the extrusion is 30.06 long x .4 wide x .2 high then that is 2.405mm³.  It is also easy to calculate the volume of 1mm of 1.75 filament.  PI x r² = 2.405mm³.  When the ratio of VolumeOfExtrusion to VolumeOfFilament is 1:1 then Flow is at 100%.  In essence "It needs this much plastic so that's how much I'm going to give it."

 

If you decide that the extrusion should only be 85% of what is actually required - then you are building in an under-extrusion of 15%.

There is no difference between calling for 85% Flow, adjusting the E-steps to 85%, or telling Cura "I want the line width at .40 but I only want enough plastic for an extrusion width of .34".

The top skin is a good indicator of Flow.  The best tool to check it with is a microscope but a magnifying glass will tell you a lot as well.  At 85% Flow the extrusions of a top skin will not be welded together and you will see the cross-hatch of the layer below through the gaps in the top layer.  That will severely impact the strength of the print.

 

But your single wall calibration cube prints will be perfect.