I had imported a .stl file into Fusion 360- from Blender, but I couldn't size it to my required dimensions. Then I tried to make an object in Fusion. It works but when I want to size it (by hitting the D key) it says:

[Error: Sketch geometry is over constrained]...

I realise if I add a sketch, that is flat I can size with D key but if I extrude it I couldn't size it any more. Same thing if I add a 3D object for example a box. Anyway I add a point on a face of that body (in the middle), then I could size it from that point to a edge but that all.

  • What did I do wrong and why I couldn't I size that body?
  • How do I suppose to size it?
  • With the .stl file imported from Blender or with the body made by me in Fusion 360?

Please help me understand how this site works with size...

  • 4
    $\begingroup$ Good evening Alex, and a warm welcome to SE.3DP. I would respectfully ask you to please not shout nor rant. Edit your question appropriately please. Maybe take a look at other highly voted questions on this site, if you require guidance on style in this matter. $\endgroup$
    – Greenonline
    Apr 24, 2019 at 19:50
  • 1
    $\begingroup$ Well done @Marco! :-) $\endgroup$
    – Greenonline
    Apr 25, 2019 at 7:45

1 Answer 1


Welcome to SE.3DP!

First off, F360 isn't the best with STL files. If you're having trouble with constraints and dimensions, I would suggest watching this Maker's Muse video first: How to use Constraints! CAD for Newbies with Fusion 360.

Second, Fusion360 is very tricky with importing STL's. My steps below should help.

  1. In the lower right-hand corner, at the rightmost end of the timeline, you'll see a little gear. When you click on the gear, click the very top option: "Do not capture design history". This puts you into Direct Modelling mode.

  2. In the top left-hand corner, where it says "Model", and select "Mesh" from the menu.

  3. Along the toolbar, in the "Create" section, click "Insert mesh". When that's done, go back to the top left where it now says "Mesh" and use the menu to go back to "Model".

  4. Now that you're back in "Model", go to the "Modify" menu. In there, find the "Mesh" section, and in that box, click "Mesh to BRep". That will convert your STL into a Fusion360 file that you can edit.

Now, if you want to use constraints, I would suggest sketching out your object entirely in Fusion, making constraints and dimensions along the way. I know it's annoying, but it'll be easier to modify it in Fusion. Hope that helps!

  • 2
    $\begingroup$ Correction: Fusion isn't the best to modify stlfiles, but it is great to make them $\endgroup$
    – Trish
    Apr 25, 2019 at 9:12
  • $\begingroup$ Also, if you use "Insert mesh" to load up your model into Fusion360, there should be an "Unit Type" setting in the "Insert mesh" dialog window. Here you can select different units like inch, cm, mm etc. So if you know what units the model was build upon you can select the correct setting here. $\endgroup$
    – LWS-Mo
    Apr 26, 2019 at 13:00

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