How to get rid of initial layer spacing between objects

[ansonl 20]

Hi, when I slice a 3MF model with 2 objects that interlock, the initial layer has extra spacing between the models that I haven't found a setting to reduce. The extra spacing in the initial layer makes too thin island segments that don't adhere well to the bed. The objects are interlocking so there should be no space between the models which is correct on all other layers. 

 

When I preview the gcode and view the second layer, the extra spacing is gone and all the printed edges of the objects line up as they should. I'm using a 0.4mm nozzle with 0.1mm layer height and 0.3mm initial layer height. I tried reducing the horizontal expansion and initial horizontal expansion to 0 but it makes no difference. 

 

I am using Cura 5.4 due to the gcode setting bug in the newer version but this spacing problem happens in both. I have attached my Cura project at the bottom. 

 

The model file before slicing. Both models are aligned in a single 3MF file and are manifold. 

 

The initial layer in the preview has extra space between the objects and the second layer to the right with no extra spacing. 

 

UM2_CA.3mf

Edited February 13 by ansonl

[Slashee_the_Cow 429]

If you could post it as a Cura project file .3mf (get it ready to print, then go to File > Save Project) that would really help. The file you uploaded only consists of a single mesh, and doesn't have your printing settings.

 

About the only suggestion I can offer off the cuff is to search the print quality settings for "expansion" and make sure they are all at 0.

 

It's also worth noting that with stuff this small: rounding can make all the difference sometimes. Especially with parts that are only one or two walls wide.

 

I don't know if this will make a difference, but try selecting the blue (rivers?) mesh, open the Per Model Settings panel:

Click Select settings and search for "tolerance". It should return only Slicing Tolerance so check that and then close the window:

and set the slicing tolerance to Exclusive:

I don't have a dual extruder printer so I don't know the joys of being able to test things like this (mesh intersections) but Exclusive makes Cura always round down so that the mesh can't exceed its defined model (at least for other things).

Edited February 13 by Slashee_the_Cow

[ansonl 20]

@Slashee_the_Cow I tried the tolerance setting but it seems to make no difference. Just to clarify, I want there to be no spacing in between the two objects so thought inclusive might work too, but it doesn't. 

 

I saved and uploaded the project attached.

CA-sample.3mf

[Slashee_the_Cow 429]

Your project file uses a printer definition which isn't included in Cura (dxu2_dual) and without that I can't do anything but load the model, yet I'm guessing by the filename of the first one you're using an UltiMaker 2? Make sure Walls > Initial Layer Horizontal Expansion is set to 0 because I think some of their profiles set it to a negative value by default (and if it is 0, maybe try increasing it by small fractions like 0.05mm at a time and see if that helps).

[ansonl 20]

Yes, my printer is a modified UM2. If you set the printer and profile to Ultimaker 2 or a newer Ultimaker, the same issue presents itself.

 

I tried have tried to set the expansion to positive and negative but it seems to make no difference. If it is set to positive, it also makes the model edges wider on the first layer which is undesirable since the edges of different models fit together like a puzzle piece. 

[ansonl 20]

UM2DD_Dual_Extruder_Calibration__Target_B_v2.3mf

I looked back at some of my other prints and the first layer gap appears on all of them to some. I attached a much smaller example that slices faster to show the issue.

 

As seen below, between the outside calibration parts, there is a gap inserted when you set one of the objects to a second extruder. 

 

[ansonl 20]

Thanks to https://github.com/Ultimaker/Cura/issues/18319, it seems like I forgot to set the horizontal expansion for the second extruder to 0 as well. 

 

The drawback of this method is that you can no longer compensate for elephant's foot that only affects the exterior edges of a print due to the horizontal expansion affecting each part and not taking into account inner interlocking objects' edges that are within a close threshold (e.g. 0.001mm) of each other.