Model is not manifold

I have drawn the model three or four times and it will not print and trying to upload it to Shapeways results in the comment thet the ‘Model is not manifold.’
Can anyone suggest why this is happening in sketchup make and how i can correct the file

2017?Cars 10-13 4mm.skp (2.0 MB)

To start with, do you know what manifold for a SketchUp model mean?


No I do not know what it means. How do I repaiar the net for surface borders and Internal face edges?

And have you been modelling scaled up with metres for mm? It’s been suggested several times before for you. [No, when I look at the file - the model is only about 143mm long overall.]

If not, you are more likely to run into problems, although that of itself doesn’t cause surface border and internal face edges.

It doesn’t help that your ~143mm long model is almost 60 metres from the origin. And that very little of it is modelled using components - only the curved roof ends.

I guess as before that you will want to have this 3D printed.

It’s MUCH easier to draw, and to fix, if you:

  1. scale up x1000 and use metres for mm.
  2. model using (sub)components to make the whole.
  3. Make dimensions whole numbers of m when drawing at x1000, or exact with only one decimal m.

It would probably be quicker to redraw from scratch using this process than to try and fix the internal faces or surface border issues with this model in the tram sides especially.

For many of the pieces, you can select one face, copy it clear of the rest of the model, and push pull it, then make a component of the result.

Then mirror or copy identical parts, and assemble them into the whole tram.

In SketchUp, a “solid” is a surface that a mathematician would call a “two-dimensional manifold”. If you aren’t a math type, don’t sweat the technicalities, just accept that it’s another name for the same thing. In essence, it is a continuous, closed surface that encloses a non-zero volume of 3D space. In SketchUp, the simplest test is that every edge is shared by exactly two adjacent faces.

If you click the ? buttons in Solid Inspector 2 you will get descriptions of what each detected defect means.

The most serious is “surface borders”, which are places where the surface stops at an edge without continuing to another face. These create holes or flaps in the candidate surface, making it impossible to tell what is inside vs outside. This uncertainty means Solid Inspector (and SketchUp) can’t tell what you intended, so you have to fix them manually. That is generally the first thing you should attack, as the borders are often also associated with other flaws or can cause false alarms about them. As @john_mcclenahan pointed out, these may result from working at too small a size in SketchUp, which can lead to loss of small faces.

Internal face edges are edges that border internal flaps or walls inside the object (internal walls divide the interior into separate spaces). Until surface borders are fixed, the detection of these is not reliable because “inside” is not well-defined.

“Stray edges” are edges that don’t play any part in defining the surface of the solid. Often these are tiny edges you created by accident, though they can also be residue from things you didn’t erase completely. They are easy to fix once you find them, though very small ones may be hard to see.

The least serious is “nested instances”. These will keep SketchUp from recognizing the object as solid, but some slicers will still work with it.

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The file I uploaded was the actual print size and it was drawn in meters and was 270 metres wid with a finished width on 27mm.

Ok then, that will have made some things easier. Sorry I misinterpreted.

And I know from trying to fix one of your earlier models that it wasn’t easy, with the geometry you are trying to create for printing.

Try again, using more separate sub components. Check each one as you finish it, with Solid Inspector 2. It’s easier to fix a piece at a time. And most slicers will accept a model for printing that is made of independent (manifold) sub components.

Make sure to get exact inferences to endpoints or midpoints as you draw, to save creating duplicate not-quite-matching edges, or holes in the ‘surface borders’.

And in particular, make the ‘half round trim’ strips separate from the side of the body, and use fewer segments in their curved surface - 4 or 6 would be plenty when they are so small in the final print. I think you have 12.

When it’s all loose geometry inside the large body component, there’s an internal face (and its edges) between the back of the trim and the face of the body. It’s possible in principle to fix it but difficult in practice, even with X-ray view toggled on.

I am redrawing the body and checking with solid inspector after each addition, so far so good.

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BTW, why have you placed your model so far from the origin? That can cause all sorts of issues!

As a followup from the request how can this file trailer 26 4mm.skp (1.9 MB) has a very small number of solidinspector faults while this file Cars 10-13 4mm.skp (2.2 MB) has over 8000 faults when both were drawn the same size and the sane method?

I have tried to draw MER 10-13 in metres a number of times and always get a similar number of faults so how can I draw it as something must have changed.

I had a quick look, and there is a minefield of straight forward drawing issues - in misaligned components, z fighting faces, reversed faces, etc. To have the whole thing as one drawing is asking for trouble. You need to go to the basics. To begin with, make groups of components, and for a start you can then replicate the paneling error free. The arc of the roof will never line up at the ends built in the way it is, rethink that also.

See how this does. I’ve just copied faces from your model, push pulled to thickness and created components for sides, central roof, internal walls, doors and some of the windows.

And I copied and tidied up your curved roof ends.

All the main parts are solid components, but a few have other nested components inside them.

I’ve copied and pasted your trim elements (made into components) but they aren’t solid. You should redraw them with fewer arc segments in the rounded profile - 6 should should be plenty.

It’s possible they will print as they are, but far from certain.

PLEASE stop using the 3D printer template. All it does is bloat your model. Start from a Woodworking mm template instead.

The model is saved at 1000x scale size.

Cars 10-13 4mmJWM.skp (396.8 KB)

Thank you for the file which seems to be ok at 4mm scale and it has been sent to my printer to see if it will print.

In a separate email, you said:

Thanks for the reworked file John but when it was uploaded to Shapeways two parts (corners) of the roof appear to be missing as on these photos (no longer available).

I mirrored those corners from one original component.

I think I understand why, but had forgotten about it when I did it. The SU STL exporter has a bug - when a flipped, mirrored, or scaled by -1 component is included, it either isn’t exported, or is done in such a way that the slicer can’t see it.

Explode that component, then re-make it in situ and that should fix it.

What do you mean By re-make it? do I just explode it the save it?

Explode one of them, yes. Then while it is still all selected, R-click Make Component again and give it a new name.

Then select the other one, but you don’t need to explode it. Just go the the Component browser, select the NEW component you’ve just made, R click on it then Replace Selected.

Then save the model, and re-export to STL.

Exploding stuff that has any significant poly count can be either time consuming of even crash material. A safer way is to copy the raw geometry (which also could take time - not here though) and delete it. Then go into the group or component you want it to be a part of, and paste in place. I use the paste in place as part of my normal work flow. When modifying designs, any number of variations can be created outside the main component, if you group them. Everything attaches but doesn’t stick, and you can colour code variants and place them on different layers to hide the ones you aren’t working on. When the best solution is found it’s then simply copy (or cntrl/move to a convenient spot) go into the main drawing group and paste in place.

Good morning John,

I have reversed the beadings on both sides of the body as the verticals are below the window pillars, moved all of the beadings to the bottom of the sides and ends as that is where they are and exploded the missing roof corners and then remade them into components so i think everything is done. Please can you check the attached file and tell me if everything is correct. If it is OK I will reduce it to the finished size and send it to be printed.



Cars 10-13 largeWM.skp (539 KB)

Fixed a couple of things.

I remade the ends into components - they had been exploded.

When I imported the STL file exported from SU to Cura, it showed one end centre roof section as unprintable.

It too was a mirrored component, so I exploded it and remade as a different component from its match at the other end.

And when I first tried, I shrank the model down to scale size, but had accidentally left the units as metres. Cura complained the model was too small to print, as it came in at 0.14mm rather than the actual size of 0.14m or 140mm.

Tried again from the large version with units as metres, and had to rotate 45° to fit on my notional printer. Now the opposite centre end was unprintable. So exploded that one too, and remade it, re-exported as STL and it looks as if it should all print.

I’ve attached both the edited SKP file and the exported STL.
Cars 10-13 JWM.stl (519.6 KB)
Cars 10-13 largeWM.skp (539.3 KB)

Thank you for your time and expertise so I am now going to email it to my printer and will let you know what happens.

Thanks for agreeing that I can publish you recent private email, and my response. It’s baffled us both as to why some STL aspects of the model didn’t work, but at least there’s now a version that looks OK on Shapeways.

You said originally that you local hobby shop reported:

I have attached 2 pictures.
1 to show the section of roof missing.
The other shows a corner that does not join the other wall.

I have also loaded it into my 3D printer software and there is something definitely wrong with the file. As I can not click on any of the walls to align it with the print bed.
This shows the file has issues, as I have not ever had this before.
Also the width of the tram is still wider than the others I have printed for you.

As the photos appear almost if not totally identical, I’ve only included one here.

My responses:

Well, I’ve no idea why the roof corner is not printing. It’s a solid component, the axes are not flipped.

I’ve gone back to your original large model, remade one end (which was just loose geometry) as a component and realigned it, rotated a copy to replace the loose geometry at the other end, and adjusted the position of the end trim slightly (it wasn’t quite on the edge).

Uploaded it to Shapeways. Says ‘fixing your model for printing’.

It’s still missing a roof corner. GRRRR!

Copied and rotated the opposite corner into position to replace the non-printing part.

Noticed that the thick part in the middle of the top of the roof wasn’t central lengthways, but centred on one of the sides. Moved it to be in the overall middle on red axis.

Tried again.

STILL missing the near front corner.

Exploded the component and made it into a group instead. both SU and Solid Inspector 2 think it is a solid group.

Tried Shapeways a third time.

It STILL omits the near front corner.

When I import the STL back into SU, it shows the centre of one end of the roof with reversed faces, and Cura thinks that is unprintable (red in the image below),

Finally, I explode and make a group instead of a component of that piece of roof, and try one last time on Shapeways.

This time, it appears to work in Shapeways, shows complete, and printable (I finally worked out how to view the model in 3D on Shapeways).

There seems to me to be more than one bug in the current STL exporter. Not just the ‘it won’t print if you flipped or scaled any component by -1’ bug which is known but still not fixed.

I can see NO obvious reason for the original not to be printable, once I had fixed the flipped or mirrored components, nor why after fixing the corner, the middle part of one end showed reversed faces in the STL export which weren’t there in the original SKP file.

All of the elements of the model were valid solid components originally, both according to SU, and to Solid Inspector 2, and only one was originally mirrored - the missing corner. And even that still didn’t work after exploding and re-making into a separate unique component, unflipped.

Please Trimble SU Team, can you see (a) why this model took so long to make printable, and (b) fix the bug(s) in the STL exporter and retrofit it as far back as possible. Or make an installable extension which can be retrofitted.

Cars 10-13 large JWM - missing corner when printed.skp (557.3 KB)
Finally printable version:

Cars 10-13 large JWM.skp (635.3 KB)

I am intrigued that the model has been deemed printable by Shapeways, or anyone else for that matter. Scaling it down by 3 decimal points means that the wall thickness is 1mm, with the panel side trim barely discernible. The copy / minus scale issue is evident on the side trim also, so best to just copy, rotate and paste the good one. Same with the roof panel. There are several overlapping and intersecting parts that could create problems in actual printing. Assuming that it will be printed in resin (as the approach would be totally different - and probably not a success with fdm), I would thicken the walls, fix the panel side trim, make sure every component is manifold, and make it all one group with Outer Shell. If it is to be done by fdm, I would break it down and print it in separate panels, and then assemble it.