Exporting .obj for 3D printing


I ordered a 3D printer today and so I started with modeling the first object to print. I managed to create a cup but when I export it to an .obj file and open it with the printing tool “Repetier-Host” the cup is flawed.

the cup in SketchUp:

Anybody got an advice how to extract objects from SketchUp for 3D printing? (Both tools are recommended by the company which developed and sells the printer)

apparently new users are only allowed to post 1 pic in a post so here is the second one:

the cup in Repetier-Host:

You ‘cup’ is probably not a ‘manifold solid’.
If you temporarily make its geometry into a group Entity Info will say ‘Solid’ in the top bar if it is.
3d-printers want solids.
A ‘solid’ is an object containing only edges and faces and every edge must have exactly TWO faces - no fewer and no more.
So, no nested groups or components, no faceless edges, no edges with one face only [e.g. around a hole or forming a ‘shelf’], no internal partition faces where some edges have three or more faces, no otherwise solid parts meeting on a common edge where that edge then has four faces, no overlaid facets [more rare but possible]…
Part of your handle has a face oriented backwards - you should never see an ‘blue’ back-sides’ !I suspect that parts of you cup have internal partitions - e.g. where the handle joins the cylinder, of where its central seam has a common internal face ?
Edit the group.
View with Hidden Geometry ON., and/or use Xray mode and/or temporary Section-Planes to access the internal parts and manually delete problematical facets etc.

Thomthom made a Solid-Inspector plugin which highlights such ‘un-solid’ problems.
I have SolidSolver which tries to fix them - although it is quite possible to make an insoluble object! - so manual fixing is needed.

Once you have a ‘solid’ group you can explode it in the knowledge that the exported geometry should be compatible with 3d-printing.

Incidentally - OBJ is one format, but STL format is more standard - there is an Exporter freely available in the Extension Warehouse…

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thanks for your help, TIG. I installed Solid-Inspector and redone the handle, it was pretty messed up.

It works fine now. I also installed SketchUp STL and exportet it in .stl. I already noticed, that most print files are .stl but I didn’t know that you can add .stl format to SketchUp as an export option


Hooray !

Now… you might want to look at increasing the segmentation of the circles used to make the cup’s cylinder, and also the handle’s arcs…
Otherwise I suspect that the3d-printed result might look somewhat ‘faceted’.

You need to change the segments when you first creating the arcs/circles [NNs typed as you make it], or soon after in “Entity Info” - BEFORE extruding the curves into a 3d form. Because once it’s 3d you can’t change it.

However, please don’t “go mad” - the default circle of 24s might be fine upped to 36s or 48s - making it ‘hundreds’ will show no benefit at this size ! It needs some trial and error…


Thanks sir, that was useful!