.stl file size?

michael_fuller

What is the primary determinant of file size for .stls?  Is it simply geometry?  Also, when exporting out, what can I tweak to reduce file size?  I usually save as "fine" as I'm 3D printing the .stl.  Any ideas what saving as one lower than "fine" will do to print resolution?  I print scale models, so resolution is king.  But I haven't done any testing (too expensive as I use 3rd party printer) to see what reducing that parameter will do to print resolution.  Anyone know from experience?  Have a 74 mb stl that I need to get below 64.  Tried eliminating some geometry but it had marginal effect on file size.

NeilCooke

Why do you need to get it below 64? The parameters - angular deviation (max angle between adjacent facets), chordal tolerance (max distance between facet and actual surface), and minimum facet width - are all dependent upon the type of geometry you are printing.

You can always try re-importing the STL into Onshape to see "how it looks".

paul_chastell

STL is a triangle-based format and scales with the number of triangles created by converting the Onshape geometry into triangles. As a result the print resolution is the way to control size. If 'fine' is 74Mb then 'medium' will almost certainly be small enough but it achieves this by approximating the geometry with less precision. Depending on the resolution of your print, however, you may find that to be acceptable.

If you want to see what it looks like you could re-import the STL into Onshape and derive the imported part into the original part studio. You ought to find that the two versions are in the same location in space. Then you can section it to see differences or use the measure tool to measure distances. 

Example here: https://cad.onshape.com/documents/3fc575c56a6b194f94e5440d/w/d552b716a661bc7a0a16d96d/e/d570f41f4fd197f2ef7e2c5b

Also I would suggest that you check that you are exporting as binary (assuming where you are consuming it can take binary), since text STLs are a lot bigger than binary ones (about 3-4 times the size). Binary STL files also compress pretty well in my experience and so if you are needing to make it smaller as a means to send it somewhere you could zip it up. Of course, if it is the receiving software that mandates a maximum 64Mb then that won't be an option.

Finally, if you are sharing it with someone else then you could share a link to the Onshape document and let the receiver download it. If you only want the receiver to see the STL tab then you could move that tab to a new document and share that.

https://en.wikipedia.org/wiki/STL_(file_format)

Ok. I got carried away there, hopefully something that I said is useful.

owen_sparks

paul_chastell said:

Finally, if you are sharing it with someone else then you could share a link to the Onshape document and let the receiver download it. If you only want the receiver to see the STL tab then you could move that tab to a new document and share that.

This is something Onshape excels at.  If the end user wants a dxf, a step file, and stl an I-Guess file, whatever, they can just help themselves to exactly what they want.  Let the designer do the designing, not the Admin. 

OwS. 

paul_chastell

Also see https://forum.onshape.com/discussion/10631/increase-resolution-of-exported-stl#latest

michael_fuller

Does the parametric history have an impact on file size?  Could I make a copy and strip that out of the copy and export as I've normally been doing ("fine") and have a smaller file?  64 mb because that's Shapeways' maximum file size upload.

NeilCooke

michael_fuller said:

Does the parametric history have an impact on file size?  

No, just the geometry

ilya_baran

No, the history has no effect on the STL file size.

billy2

@michael_fuller
I just looked at my download folder and checked stl files. None are over 64mb. I always run at fine mesh and don't worry about it.

The geometry will dictate stl file size. Rounds take more than flats.

If you like adding fillets, stop doing that. 
A cube is 12 polygons depending on settings.
A filleted cube could be a billion polygons.

michael_fuller

Tried reducing some geometry over lunch but really didn't make a dent in file size.  And I can't eliminate the fillets as that's how the object looks (multiple rivet heads).  Might have to break the file up and upload it as separate products though I really hate doing that as that requires the customer to read and understand that two products need to be added to the cart in order to get the whole thing.

NeilCooke

It's worth noting that min facet width overrides chordal tol which overrides angular deviation - meaning that if you set a large min facet width, it would not be possible to attain a small chordal or angular setting. I would not concern yourself with angular - chordal tol will get you closest to your required shape (assuming a small enough min facet width). Do shapeways use SLA or FDM? If you know what tolerance they work to you could use that to set min facet width. 

MBartlett21

Can you make sure you are exporting it as binary, not ASCII?

NeilCooke

If you share your doc URL I’m sure somebody will take a look at it for you.