Cura 4.5 Not recognizing STL Scale Factor

[DodgeDeBoulet 6]

I've created some stands for an Ableton Push 2 MIDI controller in Fusion 360. For convenience's sake I set the measurement units in F360 to centimeters. However, when I export the STL and load it into Cura 4.5, it materializes on the bed at 1/10th of its intended size. I can re-scale it in Cura by 1000% and it looks right, but I'm surprised I have to do that.

 

If I set the units to millimeters in F360 and re-export the STL, it looks normal. Here's what a cm-scaled STL looks like compared to a mm-scaled version without being re-scaled in Cura:

 

And here's the diff output of ASCII versions of the STL files (mm on the left, cm on the right; problem exists whether the STL is exported as ASCII or binary). The scaling is being set appropriately by F360, so (to me) this seems to be a Cura issue:

Edited March 11, 2020 by DodgeDeBoulet
problem is both ASCII and binary

[bagel-orb 61]

You shouldn't change the unit in fusion 360. STL doesn't save the unit in file and every program silently assumes that the unit is in mm.

 

This is a problem of the STL file format. Try using a less dated file format! Fusion should be able to.export to all sorts of format. Try 3mf.

[DodgeDeBoulet 6]

10 minutes ago, bagel-orb said:

You shouldn't change the unit in fusion 360. STL doesn't save the unit in file and every program silently assumes that the unit is in mm.

 

This is a problem of the STL file format. Try using a less dated file format! Fusion should be able to.export to all sorts of format. Try 3mf.

 

How do you account for the differences in the exponents in the facet stanzas? That very obviously indicates a change in order of magnitude, and it's obviously something that Cura is not correctly interpreting.

[DodgeDeBoulet 6]

I guess I need to eat my words ... it's apparently a change in order of magnitude that Blender doesn't get along with either:

 

So ... apologies. I understand the issue now. The exponents are actually being correctly interpreted, but the assumption is that that "1 unit" is 1mm.

Edited March 11, 2020 by DodgeDeBoulet

[DodgeDeBoulet 6]

24 minutes ago, bagel-orb said:

You shouldn't change the unit in fusion 360. STL doesn't save the unit in file and every program silently assumes that the unit is in mm.

 

This is a problem of the STL file format. Try using a less dated file format! Fusion should be able to.export to all sorts of format. Try 3mf.

 

Didn't realize Cura recognized anything other than .obj and .stl ... still fairly new to this.

[bagel-orb 61]

Sure. NP. Glad to help.

[DodgeDeBoulet 6]

FYI ... .3mf doesn't work either. I've tried exporting the model with both mm and cm set as the units, and regardless of how they're set, I have to scale it by 1000% to get it to print at the right size. This could be a Fusion 360 issue, but I currently don't have any other applications that support .3mf to test it with.

[nallath 1,120]

Could you share the 3mf file? I can have a look if it's a fusion 360 or a Cura issue.

[DodgeDeBoulet 6]

Sure, I've attached two versions of the file: one created with the units set to mm, the other with the units set to cm.

 

Fusion 360's 3mf support is provided through an add-in, which does not let you export individual bodies. Their stl support is more tightly integrated, supporting individual bodies and even launching an external application (like Cura) to process the STL as part of the normal workflow.

Ableton Stand with Logo Scaled in cm.3mf Ableton Stand with Logo Scaled in mm.3mf

[nallath 1,120]

Yup. It's fusions fault (or the add-on). Both files say that they are specified in millimeter.

[DodgeDeBoulet 6]

1 minute ago, nallath said:

Yup. It's fusions fault (or the add-on). Both files say that they are specified in millimeter.

Both files produce exactly the same result, though ... even after resetting the units in F360. The model is 1/10th the size it should be in Cura, and placed at 0,0 on the bed rather than near the center.

 

A binary comparison of the files shows major differences in content, too. But I don't know what the file structure is so I may be barking up the wrong tree with that observation.

[DodgeDeBoulet 6]

LOL it appears I am not alone in my observation. See the reviews for the add-in 😁