question about units/scale in STL export

[Anonymous]

I design a body in Imperial units, then export the body as STL for 3D printing. When I open the stl file in Makerware, it invariably thinks the stl is dimensioned in mm, rather than inches. This requires that I rescale mm->inches in Makerware. It's just an inconvenience, but I'd like to fix it.

Is there something I need to do to make F360 export to stl files that have the same units that the body was designed in? Thank you.

[deyop · Accepted solution]

The STL format does not support units.  It just records the X,Y, Z positions of the vertices for each face.  So if you are working in inches in Fusion and create the STL from within the application (as opposed to exporting from the dashboard) the positions are measured in inches.  When you take them to Makerware they are applying the X, Y, Z positions as though they were millimeters.

This is one reason we ask you what units you want to apply when you insert a mesh into Fusion.  If you had created the mesh in another application in another unit we will convert when you insert.  Makerware apparently doesn't support this?

I tried a test and I think there is a workaround you can apply prior to saving the STL file.  You can change the units of the document prior to saving the STL and then change back again.  I don't like this solution in general because it means you do have to remember to change back again after saving the STL.  After I changed the units and "Save as STL", the stl was created in millimeters.  I then needed to change my document units back to inches.

We could consider putting a conversion in the STL file if there is a strong demand for that.  Please post a request on the Idea Station if you want to have a conversion included.

Thanks

[Anonymous]

Thanks, deyop. Will try your workaround, and will post the request as you suggest.

[2herds]

New to both Fusion 360 and 3D printing STL, etc.

If I understand this correctly if I make a model in Fusion in MM instead of  Inches then export or get it into CURA (guess it seems to be in MM) then the 3D printed item would be sized correctly?

If that is right, then if threads 1/2-13 were needed, I guess I would be in trouble 😞 or at least above my mental grade.

[HughesTooling]

@2herds If you modeled in inches just change the document units to mm then export and the STL will be in mm, just change back to inches after.

If you setup to export direct to your slicer the conversion is automatic as I think it's standard for slicers to work in mm.

Mark

[2herds]

Thanks, it is working fine.

[jazzking2001]

Thanks for the answers. I just had this issue.

[2herds]

A while ago a question was generated about design in inches, then converting to MM for sending STL file to slicer.

Just tried this by making a 1"x1"x0.250" rectangle with a hole  center threaded to 1/2x13. Then converting drawing to MM, generating a STL file and sending it to CURA slicer for 3D printing.

My result was a rectangle with just about the correct X, Y, Z dimensions (within ~2 ths). However the threaded hole ID was only 0.400 short of the 0.426 shown on the design for 1/2x13 theads. (or ~29/64 drill size for tapping).

I expect something in the thread conversion inches>MM>slicer (CURA) is causing this problem, as the rectangle OD came out so close.

Any thoughts about what is going on?

[charlism]

This is not a unit conversion issue. Every 3D printer I have ever used prints the ID of holes undersized. And to make it even more frustrating it is not by a constant amount or even a constant percentage. The absolute error actually gets smaller as the hole gets bigger. The amount of shrinkage is affected by so many different factors it is not easily compensated for in the slicer software so most slicers don't even try. I have resorted to printing out plates with holes in them with my printer. I then measure the actual hole sizes in the plate and oversize the model accordingly when the hole size is critical. I normally don't try to print threads on anything under an inch and even had to model an internal 3/4" Acme thread myself slightly over sized once. For fastening functional parts together I use self tapping screws designed for plastic. Here is a forum post that discusses the problem:

https://community.ultimaker.com/topic/19550-holes-are-smaller-than-designed/

[Anonymous]

Almost 3 years later and weird controls on the save to STL still. I noticed after exporting some things and they work fine. The next day trying again and they are exporting in inches. I built my models in inches, but the first time on the first day I exported directly to my slicer. That must set some setting behind the scenes to leave the save as STL in mm, because after the first save to stl and go directly into the slicer, I can save them without the slicer and they stay in mm on the save.

[mkholcomb]

I export in mm or inch and the software I import it to always converts it to mm (I want inch). Looking into .stl file I see ..
LENGTH_MEASURE_WITH_UNIT(LENGTH_MEASURE(25.4),#15230);
so I just change the 25.4 to 1.0 and my import is in correct inch ... I expect you could convert to anything.
Maybe this will help someone.

[JeromeBriot]

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@mkholcomb  a écrit :
I export in mm or inch and the software I import it to always converts it to mm (I want inch). Looking into .stl file I see ..
LENGTH_MEASURE_WITH_UNIT(LENGTH_MEASURE(25.4),#15230);
so I just change the 25.4 to 1.0 and my import is in correct inch ... I expect you could convert to anything.
Maybe this will help someone.

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This is a STEP format entry. Nothing to do with the STL format.