Fickle 3d Tools

I frequently engrave my models with text.
I also frequently get hassled by the 3D tools wall thickness test.
It's getting annoying.
Today, it is complaining on the exact same geometry which passed in two other models.
This is the rejection today: (model https://www.shapeways.com/model/upload-and-buy/5772324)

This is one of the other models which passed: (https://www.shapeways.com/model/upload-and-buy/5545067)

The thing is, the models are created in OpenSCAD, the same code produced those areas, it is deterministic.

Here I have loaded both models into Netfabb: (one selected - green, one not - grey)

(selection inverted)

As you can see by all the z-fighting they have identical geometry.

There are only two areas where they differ.
The extra engraved logo:


and the clip style (and another logo):


So why are the 3D tools fickle?

And here is the revised one: (https://www.shapeways.com/model/upload-and-buy/5772674)

text(size=5.04) v's previous 5.02
It passed the test, but that may just be further fickleness...

Remember that the warning is not an actual rejection, but rather an indicator where you MIGHT have troubles. That's why humans take a look at your model to determine the actual printability. In this case, you can easily ignore the warning.

Read up on Voxels. The 3d tools take your model and split it into little tiny cubes (called Voxels), and then it counts the cubes to determine the thickness. The thing is.. if one model is ever so slightly offset, then the algorithm may compute the thickness slightly differently (rounding error, etc) between the two items.

By adding the text to the outer surface of the model, you are making the model thicker in one direction than the one without the text. The voxelization process starts by centering the model about the origin. That means that two 'similiar' shapes will not compute out exactly the same.. because the "center" is different between the two models.

Again, in this case, just ignore the warning.

The text in both is identical, it is subtracted - engraved into the surface, that whole lower area is IDENTICAL, but yes the other clip, in the top section, is wider, so the center thing applies.
I has assumed I could not offer for sale materials with 'issues'.
Ahh, so the yellow triangle can be ignored...Red Cross is fatal.

I would not go so far as to say that you should completely ignore the warnings. You need to become familiar with what the humans will accept and what they will not accept. Here's one of my recent models.

Thanks.
Given you can't get the human check until you (or someone) orders it, I would be uncomfortable offering such for sale, where the customer could be told 'sorry the design is bad'. So back to kowtowing to the fickle tools...

An unrefuted rule of thumb that emerged from earlier discussions is that thin areas/edges are "usually" allowed as long as they do not extend over more than twice the minimum thickness value for the material.

What gets me is the text, I think it meets the engraved/embossed guidelines (0.2mm), but the tools treat it like an unsupported wall.



Anyway...thanks for the tips.

The tool treats everything like an unsupported wall as far as I know - all local context is lost in the voxelization.