STL Export is not solid, though SU model is

I’ve drawn a part for 3D printing, scaled up 1000 times using metres for mm.

The SU model is solid, both as verified by Entity Info, and by Solid Inspector 2.

I export the result to STL, setting the Options for units to Metres.

When I re-import the STL file to a new SU model, it is no longer solid - 5 surface border problems (and a few stray lines which I removed before this screenshot).

And I can’t see why, nor see how to fix it.

Bandsaw zero clearance throat plate.stl (72.6 KB)

My Cura slicer won’t recognise it as printable - Layer view shows that nothing will print.

Any suggestions for how to fix this?

I used the same process to draw one earlier, but found it wasn’t quite the right outside diameter, but I haven’t been able to recreate with the correct diameter as an STL solid.

I also use:
It catches errors that Solid Inspector2 misses.

OK. I’ll try that. Does it work with SU2022, do you know?

Yes, it does!

This should help clear some of the errors

Is that on the underside?

Both sides.

throat.skp (87.6 KB)

Thank you very much.

I still don’t quite understand:

  1. Why the STL export fails to produce a solid - a bug? Small edges when imported back in mm?
  2. Quite how you fixed it.

Something weird is now happening when I export the throat.skp to STL, and set the units to mm.
throat.stl (110.6 KB)

All I get when I load the resulting throat.stl file into Cura is an annulus, 2280mm outside diameter!

Scaled to the correct size (68.5mm diameter, 5mm thick, it looks likes this on the build plate, and furthermore ends up only 45.6mm diam:
And it still won’t slice to show any printable layers in Cura.
Grey doesn’t print. Printable layers would be red or yellow (mostly).

Weirder and weirder.

I wonder if a restart of my computer might fix some of these glitches?

I DID succeed in printing one that worked, except for being a little oversize, a couple of days ago. But not now, and I’ve redrawn it three times from scratch in SketchUp to try and get it right. All solid in SU, not solid and not printable when exported to STL.

How about uploading your original .skp file of the thing?

Sorry, i thought I had, but when I look back I see it was only the STL file.

Here’s a very slightly modified SU file, scaled with metres for mm, and saved back to SU2017 (but drawn in SU2022).
Bandsaw zero clearance throat plate.skp (169.0 KB)

I’ve slightly blunted what was a sharp edge at 45degrees in the previous STL file.

And I’ve modelled it upside down - in use, the 45 degree bevel is on the underside of the throat.

I only opened your .skp file and exported a .stl file. i.materialise has no problem with it. I exported with units set to meters and uploaded with units set to millimeters.

I wonder why my exported STL keeps going wrong, then?

I’ll restart the computer and try again.

Dave, could you upload your STL file here please, in case I still can’t mine to work?

Thanks all for your help.

I’m not sure why yours doesn’t work.
Bandsaw zero clearance throat plate.stl (72.6 KB)

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Many thanks for your help again, Dave. Always appreciated. Have to do other things for a while, but will try to print first my most recent export after restart, and yours, Dave, if mine doesn’t work.

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When I import either my most recent export, or your STL file, Dave, back into SU to view it, Solid Inspector 2 still says there are stray edges and 5 surface border issues.

So it looks as if we’re getting the same results in the STL file. Maybe I shouldn’t worry about the non-solid STL import back into SU?

And Cura still shows only grey not red and yellow layers after slicing. But that’s on my iMac, and not connected to my printer. I’ll try it on the Windows computer connected to the printer later this evening here in UK.

I guess I wouldn’t worry about importing it back into SketchUp either. And I would suspect Cura has some issue with the file, too. i.Materialise clearly didn’t.

Looking at the STL file makes me think that the STL exporter perhaps has a less than ideal way of triangulating the surfaces. There are some very long and thin triangles where some of the faces refuse to form when the file is re-imported.

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That sounds a plausible explanation. Thanks for the suggestion.

To overcome that, I might use metres as the unit throughout, then leave the scaling down to be done in the slicer.

Though the STL was exported as metres. I’ll try importing the STL to SU in metres and see if the faces still refused to form.

You should see that difference because of the slot running out through the edge of the plate.
Screenshot - 8_5_2022 , 2_04_01 PM


All seems well on my Windows machine connected to the printer.

Here’s the Layer view in Cura:

So my worries about the non-solid STL file were overblown.

But at least one of my previous exports was both non-solid AND non-printable.

Thanks all for your input.