Filtering small objects from STL files

There seems to be some filtering out of small objects based on their volume on upload to shapeways.
(At least for STL which I use)

Here is a test I did reducing a 1mm cube to 0.7, 0.49 and 0.34 sides
Then repeat but leaving the vertical as 1mm
Then added a cylinder and repeated the process.
16 objects should appear.

View attachment 18291

The smallest cube and the smallest 3 cylinders were removed during the upload (which gives me an approximate idea of what the volume used to filter out it.

The problem is that all of the 16 objects are valid for printing with FUD, no dimension is less than 0.35mm

You can only get around this by combining manifold objects to increase the volume - someting to be aware of.

I may be able to write a small script for my modelling tool to identify these objects but others may hit this problem too.

Paul

I remember I had this problem, too, some thin parts missing after upload.

Greetings
Karl Heinz

To rule out thin parts, I tested this out with some chain maille, 0.3mm wire thickness (220 rings/shells) - it uploaded fine with no missing parts, this maybe that the rings are interlaced, so in effect there's 'one' model within the file. I've also noticed in the past that colour models have a limit to 15 parts regardless of the image map size.

Something is definately amiss.

Not sure why that'd be happening, I'll email some people to see if they know why.

Hi Paul,

Can you provide the model id or attach the file for us to look at?

Here's the test stl file I uploaded...

Thanks for attaching the file.

To answer your original question, yes we do have filtering logic to remove shells with very small volumes. This filtering is in place to remove "ghost" shells which are sometimes left over from processing a file and can cause problems for printing.

We have the minimum volume set at 0.1 cubic millimeters. Any parts that are smaller than that will be removed.

We'll make sure that this information is added to the materials options page.

Hiya tsw,

Quick question relating to "less than 0.1 cubic mm' parts - does this apply to single watertight meshes that intersect a larger part to form 'detail' that could comply with FUD design rules?

Cheers,
Paul

Hey Paul,

Parts that intersect should get merged into a single part. As long as the volume of the combined part is greater than the minimum, it would be safe from getting removed.

So for the example you gave, the small parts to form detail should be fine.

Hope that helps.

Actually that's a no - I had small "shell" objects intersecting a large object and they were removed on uploading.
The trick is to just mke them larger and intersect more.

Thanks for the info on the volume, I can now write a script to check all my parts before uploading now.

Unfortunately, they do get removed (but there is a workaround with NetFabb Cloud Service)

See this example;

A 10mm ball with 0.2mm diameter by 0.15mm studs, the studs intersect the ball by 0.025mm, individually the studs each have a volume of about 0.09426cc.

Here's what the ball with studs looks like (I've made the studs red so that the distribution can be seen)


A stud with measurements in NetFabb.


The model after Shapeways 'treatment', the studs have been removed - model page https://shpws.me/apVl


The model after using NetFabb Cloud Service to merge the meshes before uploading to Shapeways - model page https://shpws.me/apVC


Model file attached.

Paul

You are correct, and there seems to be a threshold size where the small part, even if intersecting a larger part, will disappear. I had tested on a small cube of 0.34 mm and was fine, but a smaller cube of size 0.2 mm got removed.

We will look into this.

your man/woman tsw already dais anything smaller than 0.1cc gets removed - please can we have some consistency?

Clarification:

What was meant was that individual shells smaller than 0.1 cc gets removed.

Shells that are smaller than 0.1 cc, but intersects a larger part should stay because merging is suppose to take place. Since this case isn't always true, we will look into it.

The example given by xjohnnywang was meant to be a cube with 0.34mm per side (so smaller than 0.1 cc).

Either something has changed, or there is something more complex happening here...

This model http://shpws.me/3Rrl has wheels/axles are independent, loose shells and are 0.01cm3.. that's 1/10th of the size mentioned above!

Theyand are NOT removed from the model when it's uploaded, and they print just fine, even rotate properly in the final model.

Actually, I got my sums wrong, those little studs are about 0.09426 cubic mm :blush:

They still fall into the realms of being printable in FUD though.

@Stony, The axles on your railcar mover are 'interlaced' with the rest of the model, perhaps that's the difference?