Significant Differences In Support And Model Adhesion

[malevan 1]

Encountering some printing issues when slicing with Cura 4.8, uncertain if it is a slicer setting issue or something else.

 

I'm working with a fairly new machine that tends to be a bit finicky with getting the z offset and bed levelling just right, and the model I'm slicing and printing requires a significant amount of supports.

 

Since I'd been having some adhesion issues with support printing, I've been enabling brim for supports as well.

 

After dialing in what I thought was a good bed levelling and z offset, I have wound up with a consistent pattern:

 

For the first layer, the supports and brim for supports print fine with decent adhesion. The second it finishes the supports and moves to start printing the actual bits of model that touch the build plate, it pretty much stops adhering at all. It's as if it's too high or too low extrusion the moment it switches from support structure to actual model. (It's not something obvious like a fat fingered flow rate for non-supports set wrong...

 

Any advice on how to debug this issue, anyone encountered anything similar?

[gr5 2,294]

Two theories I came up with...

 

Your retraction could be too large - it may be when it does the first retraction you retract too much and you get air in the nozzle and that causes underextrusion issues (and also over extrusion in other areas but the basic problem is the part doesn't stick).

 

Or maybe you have z hop turned on (turn it off!).  Which has your Z approach the "first layer height" from the other direction and due to backlash/play you are now too high off the print bed.

[malevan 1]

I've generally been running most of these slices with 1mm retraction, which I thought was a fairly low retraction level, though I could try cutting back more.  Better to lower it, or just turn off retraction just in case?

 

I thought I'd run a no z-hop attempt, though I may not have. Either way, I have definitely run with z-hop and z hop on retraction, and there are dozens of those Z-hops during the support/brim phase and the adhesion works fine, and it's very consistent that the problem kicks in immediately when the supports are done. Unless there is something different with the z-hop for the change, I would think that the problem would arise at any point if it was caused by z-hop.

 

(Currently I've been shifting the z offset lower and lower on consecutive attempts, and the supports came out looking printed way too close to the plate on the current print but it just started the actual model and it's got some adhesion(not the cleanest look, but adhering)).

 

I didn't think the amount of extrusion/height of printing would actually vary between supports/actual model, does it?

[gr5 2,294]

It should not.  So I'm thinking there is a problem with your Z positioning.  Just try turning off z-hop.  It should be avoided on 99% of printers.  It's very useful on delta printers.  Since your issue is on the very first layer you should know quite quickly if that's the problem, right?

 

Please show some photos of the problem because I've found that very often people describe a problem and later when they post a picture I realize I COMPLETELY misunderstood what they were trying to say.

[malevan 1]

Since I have managed to get a print that seems to be working kicked off finally, and don't have an image of the issue on the build plate, all I can manage is a shot of some of the trashed pieces from earlier attempts.

 

Basically, I had settings for what looked like good adhesion and height for Z for the support printing, but the actual model wasn't sticking at all. I repeatedly tweaked settings to lower the nozzle, 0.05 mm at a time. The model section of the print began to stick a little but insufficiently(as opposed to just being strings not connected to the build plate at all), at a pass when the support first layer started looking like it was probably a little too close(waves and ridges that look like the filament was squashed down too much by the nozzle).

 

I've attached pictures of 'first few outer wall lines of the model connected to support first layer' from I believe the last two attempts before the current attempt that has been going well for about 12 hours now(it's a just shy of 2 day print). Numbers are probably reversed(I'm fairly certain 'Print1' was a lower printhead than print2, it has much more drastic too close ridges on the support brim).

 

Once it got past the first layer, on the current print, things seemed to go with no issue at all.

[malevan 1]

I'm fairly certain that I've figured out the issue and feeling a bit silly for what I hadn't noticed.

 

This is a model I've been working on through multiple revisions, and previous revisions were printing fine, and I wasn't looking as closely when loading the placing the model in the slicer as I should have.

 

Was loading it in Cura to experiment with settings, look at the predicted travel and printing slices to see if I could figure out what was up. Realize that the entire bottom surface of the model was red, flagged as not actually touching the build plate.

 

Look at the model in 3d modeling software again, realize in my latest pass of revisions I had apparently moved a single one of the vertices on the bottom down by just a hair(less than a layer height). Edit the model so all of the 'base' vertices are on the same Z value again, and loading the fixed model into Cura, get the expected full contact blue shading on the bottom.

 

Since this is a long print, and the current session seems to be working, won't be testing this fix soon but this really seems like the root cause. Almost seems like the first layer was somehow too low for support, but too high to actually be on the build plate.