5 Years ago a 3D printing YouTuber started sessions to fix and diagnose viewer’s printing
troubles.
If you have a problem, if no-one else can help, and if you can find him, maybe you can
hire the 3DSenpai.
So let’s try this again!
A couple days ago, I asked on YouTube and Twitter for you guys to send me photos of
your 3D printer issues that I should have a look at, and you all sent in tons of stuff
with #3DSenpai, so sorry if I can’t cover it all.
I’ve picked out a couple of issues where, mostly, I want to show you the process of
identifying and diagnosing where an issue is coming from so that you can start looking
in the right spots.
We’ve got 3 cases I want to take a look at, so let’s get started, right after a
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Okay, first one, and this is a classic: Jakob Schüle is tweeting: Weird Bumps in my outer
wall.
Happening with all filaments I've tried.
Not quite sure.
Happening with cura and Prusa slicer.
I think I just forgot to turn on a specific setting.
There’s some important information in there, but let’s check out what we’re seeing
first.
The most obvious thing are all these little blobs or zits on vertical surfaces.
They’re pretty sparse, and looking at the backside here, I’d guess they’re at most
one per layer.
The light is also catching on a longer streak that looks like a bit of overextrusion along
each layer, always towards the right, or anti-clockwise around the part, from each blob.
He’s saying it’s not isolated to a specific filament, and from what we can see, it also
doesn’t look like we’ve got anything that is aligned with the movement axes of the printer
in X or Y, maybe a bit of bed bounce in Z, but that’s a different topic.
So we can rule out issues on the motion system as well as issues stemming from bubbles or
moisture pockets in the specific filament he’s using.
We’re left with the way filament is deposited, so slicer settings that affect the extruder
and hotend and of course, the hardware itself, too.
I’m fairly sure that these blobs align with the start of the extrusion path of the outside
shell, when the printer moves from printing the inner shells to the outermost one.
Typically the inner shells are being printed faster than the outside one because you care
less about surface finish and mechanical ringing when you’re adding an extra shell towards
the outside anyway.
But what can and does happen is that, because you’re printing faster, you’ve also got
more pressure built up in the hotend from the faster filament feed and when the printer
suddenly goes to the slower outside shell, that pressure doesn’t immediately disappears
when the extruder goes to a slower feedrate, but instead the hotend continues spewing out
filament at that original rate for a bit and then slowly tapers off to the slower rate
- hence the blob and the overextrusion.
So what can you do?
Many modern printers have “pressure advance” enabled and tuned in in their firmware, which
tries to counteract that laziness in the hotend flow characteristics.
But it is tuned specifically for the setup in its factory state, so with a different
nozzle or hotend, or with a worn-out or loose filament path, like I’ve discovered in one
of my MK3s, it’s not going to work that well anymore.
So check that there’s nothing worn out, but if your printer does not use pressure
advance or a similar technique, simply setting the feedrates for the inner and outside perimeters
to the same value should take care of the issue pretty well, too.
Sure, having every bit of speed tuned to the max for every bit of the print sounds nice,
but for maximum consistency and quality, going slow and keeping the hotend and extruder at
a constant steady-state is usually the safer bet.
Mausdompteur is tweeting a photo and pointing out “egg shaped holes on an old Ultimaker”.
This is a fairly obvious one, especially on an old and worn Ultimaker, but let’s go
through the steps and try and do this methodically.
So we’re only seeing the print from the top, which in this case is fine, but that
means extrusion and Z-axis problems are something we’re not really going to be able to look
at.
But we can see what mausdompteur is pointing out - all the holes that, I assume should
be round, instead are kind of an oval tilted shape - they are taller than they are wide.
The same with the hexagons in the middle here - they seem to be squished in the X direction
and if we look closely, we can also see that the sides of the hexagons also have different
lengths - the top left side is significantly shorter than the top right one.
And lastly, the infill and the inner perimeters are also having trouble fully touching the
outside perimeters.
Of course, prints like these are barely usable, but this is a fairly easy one to diagnose
- it’s backlash, specifically on the X-axis, and probably some on the Y-axis, too.
The Ultimakers have fairly complex mechanics, with lots of pulleys, belts and chances for
stuff to become loose.
The Ultimaker 3 still has essentially the same motion system as the very first ones,
and when one of these linear guides starts to bind or wear out, when a pulley comes loose
or when a belt stretches too much, you’re essentially creating a situation where the
stepper motor driving the axis will move correctly, but the actual nozzle position will significantly
lag behind and always be off by that amount of backlash.
So checking that all the grub screws on the pulleys are tight, making sure none of the
belts have any slack and checking the bushings for wear binding issues, should be the first
order of business.
It also looks like there might be a bit of underextrusion going on, the old Ultimaker
extruders weren’t the best and they come from a time where tuning a machine to underextrude
a bit for better print quality was pretty common, but that’s something that should
only be tuned in once the backlash is sorted out.
Domenico Lamberti, long time channel viewer and supporter is asking about a problem with
his Prusa Mini+ in PETG: The first layer was okay, first few layers were actually, but
on one side it bubbled up like this, almost like that side of my bed was minutely lower.
And this one’s interesting because there are a few things adding together here.
When you look at the photo, the first thing you’re going to see is what looks like two
or three large holes on the side.
But that’s actually just the result of two problems much earlier on.
Domenico is pointing out that to him it looks like the that corner of the bed is “lower”
- I’m going to stick to saying the nozzle is closer or further away from the bed, that
is a bit less ambiguous.
And if we look closely at what the first layer looks like, there is actually a very familiar
pattern that’s visible: That intermittent folding motion where each line is squeezed
down so wide that the next one actually rides over the previous one and doesn’t end up
making contact with the bed at all.
That’s the pattern you get, and it’s not a good way to get better bed adhesion.
You often also get a similar pattern when the bed surface is contaminated with fingerprints
or grease.
So to fix that, what I’d recommend is actually to raise the distance between the nozzle and
the bed, and then the good old trick if adhesion is a problem, go with a wider and thicker
first layer, and turn down the speed for that.
That gives your printer a much better chance of squeezing that first layer against the
bed and getting adhesion, even if there are imperfections in how well the bed is adjusted.
And then the second thing I’m seeing is a problem with the model, and that is that
it looks like it contains an unprintable overhang right there against the bed.
This just isn’t printable, and especially on the first layer, you’re also fighting
against the heat from the bed that’s keeping your freshly printed layer from cooling off,
meaning it’s actually more likely to curl up and cause issues further up the print - which
is what I think we’re seeing here.
So for that, a good workaround is, instead of using full fillets, using “fake fillets”,
which are a combination of a 45° chamfer and a fillet rounding over the edge towards
the top.
This is much more printable than a full fillet and if the chamfer edge is too sharp, you
can just scrape over it with a knife and create a smoother transition that way.
Now, of course, all these tips and knowing what certain failure modes look like, for
me kinda build on having seen almost every failure mode there is on these 3D printers.
If you don’t have that amount of experience, it can really help to just watch your 3D printer
as it’s printing.
You’re going to learn what it looks and sounds like when it’s working normally and
when it deviates from that, you can usually just watch the problem unfold right in front
of your eyes.
So for the folks whose print problems I talked about: I hope I was able to help you, for
everyone else: Keep an eye out for the next #3DSenpai if you’ve got printer problems,
too, but in either case I hope you learned something, if you did, give the video a thumbs
up, get subscribed if you don’t want to miss the next one, and if you really dig what
I’m doing here, consider supporting the channel through Patreon or YouTube memberships.
Thanks for watching, keep on making and I’ll see you in the next one.
Bye!