Large Tiki with hollowed head - some problems

Here’s a reprint of a model that I scaled up to see how large I could print. The final was 5.5 inches tall and had to be positioned diagonally across the build volume. I printed at 0.05. Print time was 10+ hours according to Preform (but I believe the actual time may have been a bit shorter).

I hollowed out just the head by using booleans to subtract a modified cylinder which had an extruded poly face extending beyond the chin region - so that I would end up with an air hole.

I had to fix the model first in so the booleans would work cleanly, but once done, it loaded into preform with no troubles.

I looked at automatic generation of supports, but the result was so incredibly dense, it would have taken me quite some time to strip it down. Multi-select in support-editing mode would help that immensely.

Even so, it seemed like a good test again to see if I could manage things myself, esp on a larger model. Note that I chose this orientation specifically so the supports would stay off the base - and so the fingers needed minimal supports as they grew downwards. (they were a bear to clean up on the first version of the print).

As you may guess, my first test failed. I had placed the head well opposite the hinge and it did not have nearly enough supports. The result was apparently that the forehead region separated quickly from the build platform and I had to stop the print.

Here’s the second try - I just added about 20% more supports - but very carefully placed to ensure that no “island” in a slice started printing without a support directly beneath it. It took about 45 minutes to set up, in total.

Top View

Home View

Here’s how the good print looked after removing a few supports. I had to do that to give it a proper IPA bath, as it would not fit in the IPA bin:

Uncured - IPA rinse done.

You can see above that there were problems printing the head. The head IS hollow, and the way I printed, there should not have been a blow out here, unless the wall thickness was just to much for the printer, but I have printed thicker and so I am not sure what was going on. This section was opposite the hinge again, so maybe this is a peeling problem? Or perhaps just something bad at that corner of the print? Not sure. But I see this a lot and am getting a sense for when it is going to happen (never on mid-thickness arms, legs, midsection, etc. Generally on thicker areas.)

I should say also that this same model (without the hollowed head) printed just fine at about 1/3 the scale.

(still learning how to paint… not my forte :slight_smile: )

Here’s a view of the top of the head:

But here’s a look at the slice where the problem occurred:

Slice 581

Does not seem too thick, but not sure. Also there was a hole under the chin, so even though this section remained open for quite a few more layers, it should not have had any blow outs when it closed. (FWIW this does not really look like a blow out to me, based on what I’m starting to recognize as a blow out).

Another shot before cleaning:

And some beauty shots:

(still needs a bit more clean up)

Hi Jeff,

This looks awesome! Nice work!

About the surface finish on your Tiki’s head: it’s definitely a good idea to leave a hole so that resin can drain out of the hollowed volume as you did. However, in the orientation in which you printed your model, I would recommend putting the hole in the top of the head near the point closest to the build platform. In the image you posed of Slice 581, you can see the open volume the head creates. Those walls should be no trouble, but the suction that the open volume creates during peels could be an issue. As your part prints, that volume is being closed off by the bottom of the tank which can cause a blow out.

Try putting a hole in the top of the head next time to allow for some air and resin flow in and out of the void as it prints. You can always fill the hole with with resin, cure it and sand it down after.

Good luck!

Excellent post Adam. A feature request from a while back was a hole maker tool in preform, but the response was that PreForm is not an editing program. How the hole depends on the orientation is the key. But moving on from that request, can you suggest a program that I can download to make holes in STL files?

Autodesk Meshmixer, Autodesk 123d, Blender and netfabb are all available as free programs, but for my money zbrush is the best for shelling models, which allows you to add your air holes as part of the shelling process.

Thanks Adam.

I never really "got it’ before that holes need to be on the PLATFORM-SIDe of the print. I was thinking of “draining” the resin out of the hole, but I can see what you mean by the pressure build up not being relieved when the hole is on the “tank side”. I am not sure if that bit is obvious in the support and problem solving liturature, but I will definitely read it again to be sure I have not missed anything else.

On the side - Do you think those bubbles are the result of blowouts/pressure?

I am curious why they are so localized in a roughly 1CM slice and do not continue beyond that as the character prints… perhaps the bubbles themselves create the gap for the gas to escape, and so no further blowouts happen?? (that would make sense to me I guess).

Thanks - as I am seeing a LOT of these bubble issues, I am really hoping to find a solution as they do detract from the quality of the overall print, even though they are generally in a single spot.



I do think those bubbles are caused by pressure. And I think you’re right about the bubbles creating enough of a hole to allow the pressure to be released so the rest of the head prints well.

I checked out our support material on the matter and it isn’t clear enough. I’ll make sure this is made more clear on our support site.

@JasonSpiller, thanks for the list! I will check out zbrush first.
@Adam Cool.

Thanks Adam,

I am taking a second run at this model (redoing air holes).

What I am realizing though is that, since the position of my air holes really should face the build platform to avoid blow outs, I really need to have my print orientation in the build volume clearly in mind BEFORE I finish modeling the holes. This really does speak strongly to the need for hole placement in Preform, I think. Because the process of changing a hole, especially after you have added supports (and perhaps experience a build failure) is pretty expensive.

I’m definitely incorporating this into my modeling process now. Guessing most folks are well down that path - but hollowing and punching holes in some of the more complex parts I have in mind will take quite a bit of planning in the model step. So much to learn!

Thanks again!


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Well said Jeff. Without the ability to orient and support a model before making the hole, much effort get wasted re-doing orientation and supports.