Can't join two objects for 3D print?

I am trying to make an object that is very similar to a pipe “tee” fitting. Basically its two pipes with one perpendicular to the other which are joined to form a “T”.

I cannot seem to accomplish the joining of the two pipes. They connect and always look ok in Sketchup make but when exported to STL and loaded into Ultimakers ‘cura’ one can see that whole sections of the object are missing.

I’ve literally spent hours and hours on this and tried at least 15 different permutations of ways to create this object. Every time it fails.

I would just assume that such an object is not possible to create for 3D print in SketchUp since its not a solid modeler but searching the web I have seen some examples of similar object purportedly created in Sketchup… so I guess maybe it can be done?

I’m attaching my sketchup file, the STL file it produces (with the standard sketchup stl export add on), and a screen shot of what Ultimaker’s Cura is showing when reading the stl.

Can anyone assist? I’d be love it someone can fix it and then tell me how they did it so I can reproduce.

Connector (1.3 MB)

Move the horizontal tube so that it laps into the vertical section. Then select all of the surfaces, right click and choose Intersect Faces - With Selection.

Then use the eraser tool to remove extra surfaces.

Looks like this would benefit from scaling up too.


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TheOnlyAaron - thank you for this… you’re using essentially the approach I had been trying. I just attempted again by following your animation and the first point I run into trouble is when trying to delete the center part of the merged pipes (to make it hollow where the pipe punches through). Instead of selecting only the center area for delete, it ends up selecting the whole inner surface of the pipe segment that was penetrated.

This is difficult to explain. How did you create that animation of your work? Perhaps I can do the same thing to share what happens when I try to follow…


I just tried this again and actually was able to delete the center section so it seems progress is being made. I still see whole areas missing when export to STL and load into Cura, however.

Is there a way I can determine if this is a problem with what I am doing in SketchUp or maybe some kind of problem with Ultimaker’s Cura? How do people typically validate their STL files – given this will take an age to print I really want to validate it as much as possible beforehand…


Create the first cylinder and make it a group or component. Create the second cylinder and make it a separate group or component. Cross them however you want them to be … do not explode them … leave them as two separate containers. When exporting the STL, make sure that you either select the two cylinders and check the appropriate box for “selected” or export all items in the model. Most slicers will join them together for you without the hassle of trying to make them into one solid in SketchUp. It also makes it trivially easy to make changes and export the cylinders again.

I usually run them through MakerBot or Slic3r or maybe upload it to Shapeways.

But before that, be sure to group the whole thing and run Solid Inspector!

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You don’t need to group them … if SketchUp reports each cylinder as a “solid” then the two separate cylinders need not be joined within SketchUp.

For example … three copies of a solid component:


Slic3r found no errors and sees the three components as separate shells comprising a manifold solid.

Partial proof run in Slic3r:

So… couple of things…

SketchUp does not report my cylinders as solid… I thought this might be part of the issue and spent hours trying to figure out how to make them solid but it seems I cannot make any cylinder solid. The most simple cylinder I created by drawing two concentric circles, deleting the center out of the inner circle, and extruding. Looks and acts like a cylinder but does not report as solid in entity info. Everything reports as a “surface”. The only way I can make it report as a solid is to group it. I don’t know if this is truly making it solid or not, however. It appears there may be ‘leaks’ and I think this is what may be causing the missing bits of geometry when its ultimately output as an STL and loaded into Cura.

The example with the 6 pointed cylinders above is interesting but these do not appear to be pipes – could you pass water in through one of those and have it emanate from the other five? It is the merging of cylinders, specifically, that is causing me trouble.


You’re right … after posting my reply, I realized you’re looking for hollow tubes. Unfortunately this trick won’t work since it only joins things and doesn’t remove things.

SketchUp only reports grouped items as solids … that’s the only way it knows what belongs together.

Okay, thank you, that answers a big question for me… about the grouping. So it seems I am manufacturing the cylinders correctly. And they do individually slice and print correctly on the ultimaker.

I just can’t seem to get them joined well enough to successfully slice and print. One thing though about the grouping – once I slide the two cylinders together I do have to “explode” them in order to use the surface merging features as shown in the second post above. Is this correct? Could exploding them / breaking the “solid” link, as it were, be causing my issue?

I know sketchup isn’t specifically for 3D printing… am I maybe asking too much of it for this particular task? Or do I maybe need some features found only in the “pro” version?

I’m pretty new to the application so don’t really know what my expectations should be. For now I’ll keep banging on it… but definitely appreciate any more ideas anyone has.


As @Shep pointed out, you might try scaling the model up by 10x or so before intersecting things. Scale down by 0.1x when ready to export it as an STL file.

Your model looks quite good, actually. The pipes are already solids:

The rings are solids, too:

When I slide one through the other, like this:

and open the vertical for editing and intersect the inside surface with the horizontal tube, I get a missing face:

This is typical of intersecting geometry when the results are “too small” … scaling things helps prevent this.

Same operation after scaling by 10x:

@jimhami42 … ohhh that’s what he meant by scaling… I was thinking he meant scaling down for test printing (as in to reduce the time each trial iteration takes).

Scale up for editing… This makes much sense… and the missing face as well. I will hop to it right now. Thank you.


Everyone - thanks for all your help. It turns out the process I was using was o.k. but the scaling thing was the key. Everything now slices as expected!


AND BE SURE TO PAINT THEM before doing a lot of anything to them helps keep weird spots from being declared bad . . Or having lots of open spaces that need repaired . . I do a lot of 3D printing and since I have begun to paint a lot of every thing the come out better with the solid inspector also

With SU Pro you get “Solid Tools”, but you can also find something that works even better. I suggest that you go check out the “Bool Tools 2” extension from mindsightstudios, …if you intend to do this kind of operations a lot in the future. It gives you perfect results without having to scale up, and it works just fine with SU Make.

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