Help request - I don´t know what´s going on here

#1

Greetings everybody! I´m new to the Forum and hope to get some help with the following problems

I´m currently working on a project that requires to print some really large parts. I printed at 60 µm with the Hi-temp grey and PDMS vat. And after the Moai was nearly 25 hours into the print, it suddenly stopped printing the current file and instead started to print the next file on the SD card on top of it (see pictures). I really have no clue what happened here :thinking:


The model was sliced with Asura 2.22

It was really a bummer to see this happening after almost 25 h of printing :worried:. I guess, I´ll just plane cut the model in Meshmixer where it left to print and print the rest, then glue the two parts together.
But aside from this I discovered some other issues as well. One of them being, that the outer walls of the print are not properly fused with the infill (visible on the cross section below, blue markings). This sometimes causes the outer surface of the print to delaminate, when ripped away by the peelforces (presumably), leaving those ugly holes (red arrow).

I´m not sure how to counteract this, as it seems to be a problem of using an FDM slicer instead of a dedicated SLA slicer. Another problem that is presumably caused by this circumstance, is that on some parts on the models I printed with the Moai the surface has a lot of tiny blobs. They are similar to blobbing on FDM printed parts, where the travel path of the nozzle enters or exits the object. And indeed, if I parse the gcodes in cura, those blob areas appear to be exactly where the travel paths hit the model. Those blobs are really tiny (wasn´t able to get a good picture), so it´s not that big of a deal. But it´s still kind of compromising the whole idea of having a high-res SLA printer, when you get surface imperfections like this introduced by the slicer.
Another thing is, that the color of the resin tends to bleach out pretty easily (also visible on the pictures). I only leave the prints exposed to the UV light for 10 to 20 min max. Is this still to long? I´m keeping the model submerged in tap water while curing.

Well, that´s it for now! I´m really hoping someone can help me with this. Here is my printer setup, just in case:

  • Vat: PDMS
  • Resin: HiTemp gray
  • Slicer: Asura 2.22
  • SD card: the one that came with the Moai. It was formatted about a week ago, due to another issue (caused the printer to perform an endless loop of tilt actions, instead of starting the print)
  • level: A: 10.61, B: 10.69, C: 10.84, D: 10.85
    Settings as recommended for PDMS, except:
    PM Motor speed: 12
    Laser Power: 52
    Z Reset Position: 1877

Why the hell am I not allowed to upload more than one picture! How am I supposed to properly illustrate my issues with this nonsense restriction

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#2

I think its because its your first post, try replying to the thread. with more photos.
The first thing is, are you formating the SD card using the recommend formatter?

I do a quick format before every print and only have 1 - 2 files on the card.

Its annoying I know, but it beats having a 20hr print bug out like this. Maybe there was a slight power fluctuation which caused the SD card to not read properly.

Post up the other images and we can take a look.

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#3

SLA printer behaves differently than FDM, so the kind of attention that it needed is not the same to FDM

  1. if the Moai print differently than the file, re-format it using the software provided in the SD card or @johnchen suggested
  2. you can post more pictures in the comment section if it’s not possible for you to post pictures on the post
  3. for the infill, unless you sliced the model using Cura for Moai, it’s either hollow or 100% infill
  4. the “blobs” that you mentioned are actually air bubbles, this is caused by having a hollow print without drain holes, this is important since the resins are trapped inside due to suction, without proper curing will cause the print to crack over time, leaving a puddle of un-cured resin
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#4

Here are the rest of the pictures that belonged to my first post on this topic:
The model as oriented in Asura


Here it seems as if the outer walls of the print are not completely fused with the infill between the walls.

And this seems to be the result of the problem seen above. The outer wall broke away, where it´s not proberly fused with the infill. At least I have no other explanation for this kind of failure.

Many thanks for your answer @johnchen. I´ll do as you suggest and format the SD card every time before I´m gonna start a print.

@peopolysupport thanks for the answer! I know that SLA is different from FDM and it´s good that you acknowledge that! So I wonder why the Moai is still dependent on an FDM slicer.

  1. I used the Formatting software provided with the SD card. Thanks!
  2. Thank you for clearing my account! I´m now able to reply as you can see.
  3. I use Asura, so I have now control over the infill parameter. At least not that I know of. I assume that the profiles use 70% infill.
  4. I don´t quite understand! The model was hollowed out (ca. 2.5 mm wall thickness) and had the required drain holes. There was definitely no liquid resin trapped inside! I´ll try to make a picture of those blobs I mentioned and post later.
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#5

is the 2 last pictures you sent is after the wash with alcohol?if so,one explanation for this is the resin shrinkage
after curing, there will be about 6% of shrinkage. how it shrinks depends on the structure of the model

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#6

@peopolysupport the pictures were taken after the model was cleaned and cured. But the damaged surface (red arrow) was already there when I took the print out of the printer.
Those vertical lines, that appear like cracks on the surface are actually due to tiny spider-web cracks on the acrylic plate of the vat, which of course were transferred onto the model as the laser tracks over them.

Regarding those “blob” surface artifacts I was talking about. I took a better picture of another model, where they are visible more clearly. I indicated a couple of those blobs in red:

Also I don´t want to make this thread sound too negative, because overall I´m happy with my Moai. Most of the objects, I printed so far, turned out great!

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#7

I would check your galvo cover / galvo mirrors / vat with any dust etc. looks like the problem.

How are you curing your print? it looks really over cured.

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#8

There wasn´t any significant amount of dust. I wiped everything nonetheless, except the galvo mirrors. I don´t want to touch those, if not absolutely necessary. And they looked clean anyway.

Regarding post processing, I first wash the model with IPA and then rinse it with tap water. I do that a couple of times using a soft brush as recommended. For post curing I have a bucket wrapped in aluminium foil and filled with water. I let the Peopoly UV lamp shine in from above. I keep the model in there for 15 to 20 min usually, while rotating it as necessary every 5 min or so.

The next part of my model finished printing today and at first sight, it looked pretty good. After washing it looked like this:

For post curing however, I didn´t submerge it in water this time in fear of overcuring. Instead I just put it in front of the UV light. I kept it curing for at least half an hour, while rotating it every 5 to 10 min. Even after that the surface still felt very sticky. So I cured it under water for another 15 to 20 min.
This is how it looked after that. The surface still feels sticky to the touch and it also shows this weird discoloration again on some spots:

Is this discoloration overcuring or what is it? And if so, why is it only happening on some spots even though the areas around it are exposed to the UV light for the same amount of time?

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#9

Curing in water will give you the discoloration if you have not completely remove all the uncured resin.

  • If you have airbrush, use it to blow off the IPA before curing
  • no need to wash the print in water when cleaning, stick with IPA.
  • you should submerge the print in IPA for no longer then 30sec, if you can swish it around. Have two bags of IPA,
  • I use a large mylar ziplock bag to hold my solvent
  • try denatured alcohol or methylated spirit
  • the surface is sticky means you have not cleaned the resin off properly.
  • dont forget to cure inside the print, you should cut supports before curing
  • I usually cure with peo light in a metal bucket on a rotating solar display stand ( get one, they are cheap ), then leave it to air outside under some shade for natural UV light.
  • are you using FEP vat? I’ve found Siraya Sculpt to be superior to NEX Grey in terms of surface finish. but you will need FEP for it.
  • what model is this? looks epic.
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#10

i’m glad that the previous problems seems to be gone this time, and thanks @johnchen for the help

1.for washing the print, the reason for having a sticky surface is the cause of resins left unwashed.It could be either that you didn’t wash it correctly, or the IPA batch is used over and over too many times previously.
you don’t need to wash the print with water every time you take out, only when you feel the print’s surface doesn’t sticky any more.

  1. the discoloring is also caused by left over resin, they fog up, this might happens even when the surface is not sticky. This shouldn’t be worried too much about, a layer of primer will make those discoloration spot disapear
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#11

Sorry for the late response! I wasn´t able to get back to you earlier.

@johnchen and @peopolysupport Thank you very much for your help so far!
I agree! The problem with the discoloration seems to be uncured resin, that I simply failed to wash away properly. I noticed on the second print, that most of the light spots are in recessed areas on the model, where it is most likely, that uncured resin residue might remain after washing.
In future I will pay more attention to cleaning the prints, especially the big ones. And I will switch my IPA more often.

Thanks for the detailed tips and tricks, @johnchen ! I´ll give those ziplock bags a try next time. Seems to be more efficient for larger parts.

I´m currently using the PDMS Vat, after I failed to get the bigger parts printed on the FEP.
If I can get may hands on this Siraya Sculpt resin, I´ll try it!
I was actually thinking to get one of those Z Vats for my Moai. Do you have any experience with those?

Thanks :smiley: It´s gonna be part of a Diictodon Diorama, that I´m currently working on for a customer. Diictodons were small ground dwelling reptile creatures, which lived during the permian period (about 250 million years ago). They were kinda like mole rats. I sculpted the model in ZBrush:

The first one is already printed completely (aside from the little tusks)

But aside from that, your models are quite amazing as well! I took a look at your Youtube channel. Fantastic work, man! I´m especially fond of that Godzilla model you did. That´s just epic!

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#12

your project looks amazing, very nice work. Thanks for checking out my youtube!

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