Website Update: New Volume Calculation

We’re about to change some calculations in our 3D upload and pricing software. As it may impact the pricing of your objects, it’s important that you spare a few minutes to read this article.

Internally we call this change ‘multiple shell merging’. What this means is that we fuse loose parts (or ‘shells’) into single objects wherever possible (for the techies: we do a Boolean union operation).

Change 1: Overlapping parts are no longer charged double.
An easy way to attach two objects is to make them overlap. In the old situation, our software would calculate the printing costs of each part and add them. This meant that the overlapping region would be charged twice. In the new situation, our software sees only one volume and it’s priced more accurately. See the 2D image below for an illustration.

Change 2: Hollow objects without a hole are now regarded as solid
A common trick to create hollow objects (one that we even suggested!) was to create a smaller object inside and flip it’s normals. This would often lead to a closed space on the inside, where excess material would remain trapped.

Because of the shell merging, these ‘negative’ objects are now discarded.

This can be easily avoided by creating a small hole in the object’s wall. This will cause our software to see the ‘inside’ properly as ‘empty volume’, and will subtract it from the printing price.

Tip: The hole doesn’t actually need to be large enough so that we can extract the excess material. 

Will these changes influence my existing models on the site?

Everything that you have already uploaded will keep it’s old price, and only new uploads will be affected by this change.  In the future we might recalculate everything, but in that case we will contact you if there is a negative impact on specific models you own.

When will you guys change this?

The new software should be released later this week next week. We’ll announce the release on the forum.

Why are we changing these calculations?

We did not have the software before! This is also fairer we charge closer to the cost.

With everything we do, we work towards lowering our printing prices. In the old situation, our operators had to merge the parts manually before printing. By removing this step we can make the printing process faster and therefore cheaper.

On top of that, we’re glad to have resolved the issue with pricing of overlapping volumes. This can directly influence (and improve!) your printing price.

16 comments

  1. Mike Armbrust

    I thought that hollow objects already were calculated as solid? Also I can’t wait for this update! It will allow so many ideas to be made without having to boolean complex objects.

  2. fracai

    Does the overlapping calculation have any effect on pieces that overlap themselves? Such as a continuous, solid tube which curves back on itself. I presume that the new overlap calculation is merging distinct pieces and won’t detect this case?

  3. Stannum

    Do holes have to be part of the mesh or can they be built from multiple meshes with different normal orientation? Take the top image, left side, and imagine one of the shells is reversed. Will it print and be billed as a square with one missing corner? As a full square? As the two squares joined like in the right side?

    1. Robert Schouwenburg

      That is a hard question. It depends on a number of factors like the surface area of the shell / mesh.

      But if you take the example from above the mesh with the inverted normals will get fixed and you will get two joined cubes.

  4. Mark Holtkamp

    I can see how this helps people but for me this is bad news. I create geometrical models with flat faces, that cannot have holes in them. I use the hollow object “trick” as described above to keep the price of my models acceptable.
    Ok so maybe it is possible to create tiny, hopefully invisible, holes in my models. I don’t know. But my models will look the same, cost the same, print the same. So this brings me nothing, only extra work.
    Anyway in the sentence “This can be easily avoided by creating a small hole in the object’s wall” I’d leave out the “easily”.
    Maybe it is possible to leave the current volume calculation and the hollow object “trick” available as an option when uploading models?

  5. Andreas Woody64

    I like that., because it makes designing easier.
    Maybe you should consider a button for redoing the calculation of an item for users which want to use the new algorithm.
    Can also be achieved by uploading a new version (the latest design) once more.,

  6. Mike Armbrust

    I just uploaded a model and either this new system is amazing or it doesn’t check for manifold errors. My model externally was correct but it had horrible errors in Blender. If the new system was able to just fix it up that’s amazing!

  7. Derek Bosch

    I agree that adding holes to meshes isn’t always easy for hollow parts…
    I really wish there was an option to keep things hollow…

  8. lukas

    By now I used excusively OpenSCAD for my models which does the whole boolean merging for me, so this update does not mean any direct price reduction for me.

    Regarding the closed space trick:

    I recall to have seen a video where someone suggests it.
    I think it was about leaving the support material in a puzzle consisting out of the detail material.
    But is it really ok to do that? Especially in the other materials I wonder.
    I mean the supporting material there is the building material itself => same cost for you.

    So, suggesting cheating but making it harder at the same time … clever.

    1. Stony Smith

      There are two costs to the process: 1) the cost of the material, an 2) the cost of time/energy to run the laser. I would hazard a guess that the cost of the material is smaller than the cost of running the laser.. that’s why you can get away with this ‘support material’ concept and not hurt their costs much.

    2. lukas

      But the time needed for a specific print should also be proportional to the volume (if the entire printer volume is filled up every time).

    3. Tom van der Zanden

      For the detail materials, the support material has to be discarded anyways. For SLS, the tiny amount of material that can be trapped is not worth a lot compared to what is wasted to begin with (they can only recycle x% of powder or the prints will turn out bad).
      If a part is hollow doesn’t affect print times by much: for SLS, the lasers scan time is very small compared to the time laying down a new layer takes. For other printers, it doesn’t matter whether you’re depositing support or build material.
      A big part of the cost comes from the people operating the printers and cleaning the parts. For them, having an enclosed hollow is probably better than having a cleanable one because it takes less work to clean.

  9. Baumann Eduard

    I’m glad to hear this because my models had up to 50% overlappings.

  10. Shapeways Blog

    We just released the ‘Multiple Shell Merge’ feature. It was announced on our blog earlier and it should save you some money. It took some time to iron out the last wrinkles, but we’re happy with the results now. There’s just one catch: it doesn’t work f

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