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I have this exact problem too. Does anyone know the exact settings in Inventor that need to be changed? Don't want to play with scale in Cura, because some parts are designed to be an exact size.
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I know this is an old thread, but the answer might eventually help someone out.
There's a couple different ways to go about it.
The default STL export settings in Inventor will always assume that the document units are the units you're intending to use for your export. If you created the design using a millimeter-based template, you're fine. Anything else, Cura's going to assume you used millimeters and that's what it's going to give you.
First option--and this works for both IPT and IAM files--is to go to the TOOLS tab, then DOCUMENT SETTINGS and click on the UNITS tab, and change the length units to millimeter. It won't re-scale your part or change any dimensions- it'll just convert everything to metric. Any .250 dimension will become 6.35mm instead, for instance. I don't like doing this, because I think in multiples of 1/32 and I don't want to confuse myself later, so I use...
Second option: export the thing with millimeters. This is a little different depending on whether you're working with an IPT or an IAM.
For an IPT file: ENVIRONMENTS tab, 3D PRINT. This is your default environment for working with 3D prints. Click STL, and then at the bottom by the SAVE button you'll see OPTIONS. Click on that, then set units to millimeter. (I'd also set the Format to Binary, and resolution to high or medium. I've had issues with smoothly curved faces coming out faceted when using BREP as the output, and I've occasionally had Cura barf on an ASCII STL file output from Inventor, but not often.)
For an IAM file, go to the 3D print environment the same way, but you'll notice that things look quite a bit different. Use the pulldown menu to make sure that your output is set to STL, and then click the options button. At this point, the menu looks the same as it did for an IPT file, and you set the options up the same way. (Mostly- sometimes but not always I find that the ASCII STL files are the way to go with assemblies. No idea what makes them different from part files, but sometimes they work better as ASCII than binary.) After this, on the left side of the tool bar, click on SEND TO 3D PRINT SERVICE, and then you should be good to go from there.