Blender -> STL: Missing parts after join

Hello

First off, a thank you to everybody at Shapeways and to all the designers for a great facility!

I have started some modelling and am quite happy with my (still somewhat amateurish output).

But I have a question:

I use Blender and export to .stl for upload to Shapeways. Works fine overall and I can figure out most problems. But there is one that has me baffled.

I model vehicles and airplanes by designing the separate parts (e.g.airplane hull, wing and engines) as separate objects, then I do a join ( CTRL-J ) on all the pieces and export to an .stl file.

When I upload to Shapeways, I often find that some of the joined pieces are missing in the model displayed by Shapeways on the website. When I re-import the .stl to Blender everything looks fine. Minor modifications can cure the issue with a model, but I find the behaviour quite unpredictable. I have had this problem with several different models, none of which I consider especially complex.

Is this just an issue with the display program and the model will 3d print correctly? Or will it only print what we see?

An example are these models of a tank:
https://www.shapeways.com/model/391820/hs30_test02_b.html?gid =ug

https://www.shapeways.com/model/391572/hs30_test02.html?gid=u g

On the second one, several wheels are missing, the other has all the wheels, but a radiator plate on hull top is not there.

Any hints or suggestions?

Greetings
Karl

1st in blender to export to STL you do not have to join the objects... they don not even have to be on the same layer-

when you export though you have to have everything that you want exported selected when you do export...

this might fix your problem... or might not...

2nd what i think you are describing though is that the polygons are turned inside out. this sometimes happens when you join objects... you can't see it because blender is rendering on screen as if the polygons are 2 sided... but the STL and shapeways will only read one direction(the normal)...

so to test fist try exporting without joining the parts... if that works oyu are home free... if not chose the part that is not coming in- select the polygons- then flip them by using the left hand side command panel.... and re export... if this comes in properly then there you go... if there is any more issues... let us know...

chris

Thanks for the quick reply.

I will try the suggestions and see what happens.

Greetings
Karl

Besides checking normals be sure to see if the objects are a manifold mesh(watertight). You can also display face normals from the property panel. Sometimes recalculate normals doesn't take care of all of them. you can manually flip the offending face normals

I have discovered another reason why parts may not appear in a model created in Blender/stl.

When you copy parts in Blender and hit Shift+D (Duplicate) once too often, it may happen that you end up with two identical parts in the same position. Such double parts disappear when you upload them to Shapeways.

This is easily solved by removing the offending copies.

It is rather hard to spot, as the model looks completely normal in Blender, but you can check the list of objects to look for duplicate parts.

Greetings
Karl Heinz

I had exactly the same problem,- unfortunately it was such a small support pin that was missing, I realized days after I had the model received. I could not see that in the mini-website viewer.

Netfabb did not fixed or find this, but it highlited the doubled pins, so I could pinpoint them. Anyway it is very odd, that if something is doubled vanishes in the shapeways process phase.

It would be a great advantage if I could download the processed stl file from shapeways to inspect it before it is printed. The one that is archived on the servers is obviously the one I uploaded.

Ummm....
We already can download our own files !?

He wants the processed file (merged shells, fixed normals, etc), not what you upload.

Yes, exactly. I added it as a feature request here

Shapeways runs MeshMedic during the upload process, which means that are the processed files...
Or not ? :neutral:

I compared the md5sum of the downladed and the uploaded stl,- they match. So this seems to be the original file.