Multipart print join alignment problem


#1

This issue is with the Peopoly Moai 3D printer and multipart prints.
The parts do not align properly and/or are distorted/warped, as can be seen in the attached image.

My workflow is the following:
Model in ZBrush -> Export to Meshmixer (Analysis->Inspector->Auto Repair All) -> Export to Asura (rotate to about 45 degrees, place in green part, generate supports, export to Peopoly Moai 100um 35 with no calibration selected).

What we did notice was that the first layers on all models seem to come out rougher and more rugged. I’d attach pictures, but I’ve reached the limit for a new user.

What could cause the alignment issue above, though?


#2

Resin shrinks during the curing process, which can warp or change dimensions if a print. Orientation of the model, lack of vent holes, and improper or insufficient support may also distort a model.

The first few layers of the model are intentionally overcured and compressed to improve fixation to the build plate. While it is better to print a model off the plate, you can account for this feature and print directly on the plate.

BTW: are you using the FEP or PDMS vat?


#3

Thank you for your quick response.

I can see how curing might affect it, but the model is pretty big (hence the multipart print).
Would not expect it to be off by 5mm as it is. Is it normal?

Any suggestions where to read up on properly orienting, venting and supporting models?

PDMS.


#4

Resin shrinks by % of volume also, so thick stuff may shrink more, depending on how the forces end up within the object.


#5

5mm is a lot. However, there is another element in the mix: the slicer. Did you scale the parts together (i.e. as one print) or separately?

However, as sdodds rightly points out, depending on the structure of the parts, they may have shrunk at different rates or in different axes.

As for information and tutorials, I would check out this forum, the wiki, FormLabs’ tutorials, and the excellent videos by Model3D. Model3D’s videos are published on YouTube (sorry, I cannot do links). You want the “How to Resin Print” series (it’s 2 videos)… These should get you started. Welcome to the adventure that is SLA.


#6

the resin shrinks when cured, sand it off a bit then it would be fine
it may not be possible if you want your print to be on exact dimension after curing


#7

@Paradoxical_Cat: Yes, 5mm seems a lot indeed. That’s why the suggestion from peopolysupport (no more than two mentions) is not really viable, considering we have a joining mechanism (hole + peg), which does not align when such big warps exist.
The parts were scaled together in ZBrush. They were imported separately into the print, but no scaling there (in Asura).
Thanks for the warm welcome, though. Appreciated.

@sdodds: I like the theory about thick/filled models. Still, we did try a very small (4cm) hollow 3DBenchy and it still did not align exactly, although it was way better. Not sure whether this is proof.

What I gather from this so far is:

  1. If possible, make the print hollow (so warping from curing does not affect it so much).
  2. Put supports away from the joining face, i.e. where the peg/hole is (so it is not deformed by them).
  3. Rotate/orient object properly considering the above (so it is as far away from the first layer as possible).
  4. If possible, keep joining face parallel to (so it warps consistently) and away from (so it is not the first layer) the printing surface.

Does this sound reasonable and does anyone have anything to add so far?


#8

there is couple factors at play here:

  1. resin shrinkage, which is by volume, not by axis, or about 6-7%. so each axis is about 1.5%. this is very typical of acrylic resins (which is basically 90% of all UV resin for 3d printing). the shrinkage also depends on center of gravity where the further the part is from its center, the more shrinkage but this effect is not as obvious. 1.5% for axis is not that big so it would not contribute to the 5mm difference

  2. a much likely factor is the distorion on x/y plane. based on your answers, you did not use calibration in Asura. For get the best dimensional accuracy, it is best to go through Asura calibration: http://wiki.peopoly.net/doku.php?id=moai:asura At the very minimal, you want to calibrate your glavo using
    Advance Moai calibration guide:
    https://drive.google.com/open?id=17EYM9WTy9HMLh6x3lLFIOnQ_dxqDnTRWgukOVBkIxvg

once these are set, all your future prints will benefit


#9

We will try this calibration out.
Hope it works. Will write when we have some meaningful results with all the tweaks.