STL Export Scale Factor is Wrong

SketchUp 3D Printing
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1

I recently changed to working in meters instead of mm. This solves some problems I was having with sketchup, but introduces a new issue.
When I export the printable object, I export it with units set to mm. This should scale the object by 0.001 to change from meters to mm. Cura seems to import it correctly, but when I switched to Repetier Host I ran into a problem. The object was apparently scaled by 1000 instead of 0.001. Telling Sketchup to export in drawing units (meters) and telling Repetier to import in mm gives an object that is the correct size. Clearly I can work around the issue.
I have communicated with the author of Repetier Host and he confirmed that when set to mm Repetier imports without doing any scaling.

2

Changing the units in SketchUp doesn’t scale the model in any way. It only switches to showing the dimensions in differnt units. Typically, 3D printing systems let you specify the unit used when importing the STL file.

Anssi

1 Like
3

There were two things going on here. I am increasing the drawing units and
then expecting to scale back down to mm on export to the slicing program.
The scaling that I am complaining does not work correctly is the scaling of
the STL export plug in. The fact that it has a menu choice of units implies
that it is re-scaling on export.

According to Dan Rathbun scale factor in Sketchup does more than change the
units displayed. Below is a quote from an email he sent me.

"Are you drawing at full scale or 100x or 1000x ? There might be issues
with small faces, etc. (SketchUp has an internal tolerance of 0.001 inch.)
So this extra time “wheel-spinning” may be SketchUp choking on coincident
points, etc.

It is often recommended to set the model units to meters, but think (and
enter measurements) as if units were set to millimeters. Later when
printing or exporting you can scale the whole model down 1000x."

I appreciate your effort to help with the issue. Dan’s advice seems to be
correct in that drawing problems with small curved surfaces intersecting
are not evidenced when drawing in meters instead of mm. Also I have noticed
that saves are a lot faster with the larger geometry.

4

Very interesting. From time to time, I 3D print models from SketchUp, and when I want to print a building at a 1:500 scale, my workflow is as follows:

  1. In the project file where I model the building (units: centimeters), I group the building I want to print.
  2. Inside that group, I draw a 500 cm line using the pencil tool.
  3. I select the Tape Measure tool.
  4. I measure that 500 cm line.
  5. I type 1 cm on the keyboard.
  6. I open a new SketchUp file using the “3D printing – millimeters” template.
  7. I copy the scaled group into this new file.
  8. From that file, I export to STL.

This way, the scale and units are correctly interpreted in Cura and Bambu Studio (Orca Slicer).

Or the second method:

  1. I change the units to mm.
  2. I export to STL.

This way, the slicers also load the STL with the correct units.

That means slicers expect models to be in millimeters, and changing the units in SketchUp affects that.