3D printing size does not match

[thburn]

Hi,

I created a small object using Inventor 2013.

The base of this object is just a cylinder with diameter of 3.599 mm. (see attached image M1).

Now I wanted to 3D print this object. Inventor creates the *.STL-file.

The Inventor 3D print dialog shows a witdh and length of arround 4.12 mm by a scaling of 1.000 !?!

Why it is bigger than what I created? It should be 3.6 mm.

If I upload this to shapeways they show also 0.4 cm width / length. So my object will printed a littlebit larger than I created !?!

Even if I change the resolution inside the STL-dialog it does not change anything.

Can someone tell me why the STL-Object is bigger than the model I created? What am I missing?

Thanks a lot!

[JDMather]

Inventor defaults to cm as the stl output (and doesn't do a units conversion).

When saving the stl file be sure to click on Options and set the output units to the document units.

[mrattray]

If that was the case, then wouldn't he be getting a reported size of 36mm?

[JDMather]

I didn't look at the attachments.

I have never seen that dialog box (in english).

[SBix26]

JD, that box comes up when you select Print > Send to 3D Print Service.  For the part that I tried, which is modeled in inches, the Length, Width & Height numbers are accurate, and read in inches.  But the Options still say centimeters.

Sam B
Inventor 2012 Certified Professional

Please click "Accept as Solution" if this response answers your question.
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Inventor Professional 2013 SP1.1 Update 2
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[JDMather]

I have never used that method - I always use File>Save Copy As and the OP indicated Export>

I did some experimenting.
If I create a cylinder then x and y are equal in that dialog.

If I cut from the cylinder in y direction y is bigger even though y max on the part is the same.

So my conclusion is that dialog is returning some boundary box size related to how the part was modeled and not the actual dimensions of the part.

We have 3D printed thousands upon thousands of parts here and as far as I know are printed parts are the correct size.

We have found that reading the stl file back into Inventor is not a safe check as there is a bug I have documented here before.

[thburn]

Hi,

thanks all for participating and trying to help.

I found also out that the size is correct after creating the STL-file. Which means 3D print servives such as shapeways seem to create correct sizes of the object. The problem with shapeways was that they round the 0.36 to 0.4 which exactly matches the length and width of the STL dialog inside Inventor.

I cannot remember where but on other page of shapesways the size is shown using more decimal places and it shows 0.36 cm which is the correct size I need.

It seems that this is a problem of Inventor 2013 inside the STL dialog.

I also wonder that the STL-dialog shows the correct height of 36 mm. Only length and width are different (0.41) compared to the original object (0.36).

I don't know if someone from autodesk listens to this forum and especially to this thread may they can examine this problem more detailed and provide a solution?