Saving a model loses surface edges

I am an industrial designer and use SU to create systems products for a large furniture company. We work on things that as an assembly can be of architectural scale but are made of things that are very fine scaled. Often I create models of aluminum extrusions that have very fine details, small radii in particular.

I often import DXF files from my engineers from ProE which is always a 2D model with excellent line continuity. I generally import them at a large size, if the model is in mm, I will set the import units at yards or similar to have all of the detail import properly and not suffer the loss of lines on arcs etc. I will then use “add faces” to create the faces and then resize the resulting faced, 2D element to the size it actually should be.

The bug I often run into is that when I save the file, that SU will unceremoniously delete the now very small line segments which make up the outline and I lose the surface of the object.

The same happens if I copy and then paste the faced object into another SU model.

If however I Push/Pull the face, it will keep all of the faces. Usually.

It would be nice if it would keep the data integrity despite the small size.

How small is small? SU has a problem with very small things. Hence the Dave Method.

Quite small, the issue is even using the ‘Dave’ method, when I go to save the smaller line segments will disappear along with the surface.

However if as I said I extrude the surface before saving, it will keep the faces and the small lines as part of the now 3D model.

There are just times when I just need the surfaced, 2D model with the lines intact to export to have steel templates lasered out by my model shop.

You might need to look at your export settings. For example you can model in Meters and export in Millimeters.

you are still best served by exporting 3D as it preserves arcs and curves…

I push/pull up to material thickness, group cuts on a layer and group engraving on another…

set color by layer with red and green, then PP + Top view, export 3D…

occasionally I have been ask to add location pins for repeat jobs and they go on there own layer as well…


Are you fixing problems when saving? Saving itself should not alter the model in any way, but agreeing to fixing problems can cause problems with geometry smaller than what SketchUp was originally intended for.


That is very interesting. I had never noticed that it would do this, I had automatically fix problems on in the Prefs and did some tests with it on and off.

With just the line work or line work and a surface with ‘fix problems automatically’ checked it will delete all the small lines that make up the profile.

If I uncheck the preference, it will save it but tell me that there are problems but allows me to fix later. When I open the file it lets me know it has problems and offers to fix them and then promptly removes the small lines and the surface of course.

Unfortunately, ProE outputs DXF’s that are only 2D and to add insult to injury uses line segments rather than arcs to in its output. (or at least those are the presets out engineering group has).

Thank you this was a good learning and offers a work around until I do choose to pull it up into a 3D object.


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I use to import ProE stuff in meters and exported in mm, i.e. I never changed from meters in the skp…


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I just got hit by this bug. I scaled the image up by 10x, and the problem went away.

I tried modeling in meters and exporting in mm, but the STL was is still just sized in thousands of millimeters instead of automatically scaling down by 1000.

Export the STL in model units (meters) and import it into the slicer program as millimeters.

I don’t see any option in PrusaSlicer to set the import units.

If your slicer won’t let you do that, then you’ll need to scale the model down prior to export. Most slicer programs do allow the user to determine the units when importing the STL file. STL files on their own are unitless.