Z-scars? Or something else?

[thegammaray]

Hi guys,

I've had my M2 for a couple weeks now. I have a couple questions, but I'll probably start different threads for each. I'm enjoying the printer so far!

I did a series of test prints using the owl while experimenting with different variables. It was a learning experience, but I didn't realize until afterwards that infill is the common denominator between all of my owls that have imperfections on the back surface. I've attached a picture. As you can see, the pattern is identical on the three leftmost owls, while the two on the right were printed without infill.

Is this a z-scar? I'm familiar with the concept, but I don't understand why it would only be apparent in those specific places with infill. Is it because the overlap between the wall and the infill deposits excess filament in those spots? If so, then why don't I see it all the way up and down the model? If it's not a z-scar, what's causing it?

Finally, how do I prevent/minimize that? I've resorted to printing without infill for now.

Thanks for your thoughts. (And thanks to all those who posted in my previous thread!)

[insta]

How many exterior perimeters are you using? I generally use 3-4 to help with that. Coast will also help, up yours by 0.2mm until those marks go away.

Also, either those are really tiny owls or really fat layers -- which is it?

[Kulturfolger]

Software: Can you show us your settings? To much infill overlap creates trouble. Z-Lift while travelling takes to much time. The temperature might be to high or you are printing to fast.

HW: 1) Mabye the screw holding the direct extruder teeth thing gripping the axis from the gear went missing/loose? I had it a couple of times with direct extruder, these screws tend to make a hole into the steel-axis. This usually leads to a loose screw. 2) On the other hand the tension on the idler might change over time and your e-steps might be wrong. 3) When I look at the bottom layers there might be backslash involved, the left and right part should form a perfect angle but its shifted. Its exactly the same on the two left owls.

[jsc]

Those zits are caused by the beginning/end of layer. From time to time, we have had people come and go trying to optimize settings to make them go away, but the best I've seen anyone do is minimize them.
Different infill will change where each layer starts if you have the default layer start setting, because it can change where S3D thinks the "best" starting location is. My preferred option is to change layer starts to the "closest to" setting and move that point to a location where it will be least noticeable. That will create a seam all the way up the object. If I care about having a perfect surface presentation, I will sand that seam, coat with XTC-3D, and paint.

[thegammaray]

Thanks for the responses! And sorry for the delay. I've been doing experiments whenever I can get some free time. I have a forest's worth of owls at this point.

I've played around with coast settings, temperature, speed, outer layer number, outline overlap, etc. and... honestly, in a blind test I don't think I could tell the difference. The scars/zits haven't improved. I guess the good news is that I don't need to worry about making the problem worse with per-project adjustments...

Here's what I don't understand, though: why doesn't it happen when infill is disabled? The scars/zits definitely happen at the layer change point; I've watched them. But when I turn off infill, the owls look pristine. With 4 perimeter layers, what is changing relevant to the outermost layer when I enable/disable infill?

@insta: I've been printing these owls ~38mm tall, so the layers might look bigger than they are.

@Kulturfolger: I can't post one collection of settings because every owl has used a different combination. My variables for the first set of owls were infill %, temperature, speed, and layer height. I didn't start fooling around with coast and outline overlap until after I read the responses in this thread.

[3dPrintingMD]

Few things. I agree those layers seem to be quite fat, almost as if your extrusion multiplier isn't right. I'm going to assume that you have calibrated that and you are good there.

As for the Seam, I am working on this all the time, its never ending to a degree. With that said, the reason you don't see it when infill is at zero is most likely the hot end never really moves from position. What I am trying to say is that it just goes around and around and around, verse going around, moving to do the infill and then moving back.

As noted the seam is created by either or both the ending and beginning points. So, some tips.

1) In your layer tab under start points, you can choose the 3rd option, I set mine at X100 and Y250, this will put the seam on the back of the object, directly in the middle (assuming the thing is centered on the table).

2)Under the extruder tab, use retraction, and wipe for starters. The wipe essentially will knock down any high point in the beginning or end. Use little values, I've been using .01mm for both the coast and the wipe.

3)Under the Advanced Tab, Go with Force Retraction, and Perform retraction during wipe.

Keep testing !

[jsc]

Check out Simplify3D's new visual defects guide for some suggestions, too: https://www.simplify3d.com/support/prin ... s-and-zits

[Jules]

I've seen something happen in the latest version of S3D when you print with more than one outline, with the direction of the outlines going from Outside to Inside.
Instead of moving over and continuing around the circle in the same direction, it doubles back and goes the other way on the inside when it does a double. But it doesn't always overlap when it doubles back, leaving that little gap at the starting point. Drives me absolutely nuts.

Try using just one outline. And change your outline direction to Inside to Out, if it isn't already set up that way. (It should be anyway, because of all the overhangs on that.)

I'm printing one now at 38mm, and I'm not seeing the problem. (Thought it might just have been the shape....sometimes the organic shapes are hard to dial in correctly.) If it prints all right, I'll post the settings, if you want them.

Update: No divots, he turned out okay.

PLA Settings

Extrusion Width: 0.4 mm
Retraction 1.0 mm
Extra restart: none
Retractions Vertical Lift: 0.20 mm
Coast: None
Wipe: None

Layer Height: 0.2 mm
Top Solid & Bottom Solid: 3 each
Outline Shells: 1
Outline Direction: Inside-Out
Optimize Start Points for Fastest Printing Speed

Infill:
Fast Honeycomb 20%
Outline Overlap 15%
Infill Extrusion Width: 100%

Support: None

Cooling:
Full fan after layer 1

Speed Overrides:
Adjust printing speed for layers below 15.0 sec: Checked (yes)
Allow speed reductions down to: 4%

Speeds:
Default Print Speed: 4200 mm/min
Outline Underspeed: 80%
Solid Infill: 100%
Support Structure: 100%
X/Y axis: 12,000 mm/min
Z axis: 1200 mm/min

Advanced:
Only retract when crossing open spaces: Checked
Force retraction between layers: Checked

Everything else should match your settings from your calibrations. (Z-Offset and Extrusion Multipliers, etc.)

[3dPrintingMD]

Just for fun, I'm going to give this a print as well using those settings.

[3dPrintingMD]

Well I could not replicate your results. I ended up with a Z scar similar to the OP.