I am trying to print this really cool flying toy model on my ToyBox 3D printer, but when I try to print the "copter_key-175.stl" file it complains it is a "non-manifold shape". How can I fix this .stl file?

[update START]

Update for future readers: I haven't tried it yet, but the Free and Open Source slicer software, Slic3r, boasts this feature worth trying:

auto-repair of non-manifold meshes (and ability to re-export them);

Update again: the best slicers, it seems, based on my research, are:

  1. Cura (FOSS and professionally supported),
  2. PrusaSlicer (FOSS, forked from Slic3r, and also professionally supported now).

Articles to look at:

  1. Google search for "slic3r vs cura"
    1. Slic3r vs Cura (Cura wins; Slic3r lags due to no full-time company-sponsored development): https://all3dp.com/2/slic3r-vs-cura-3d-printer-slicer-software-shootout/
  2. Google search for "prusaslicer vs cura"
    1. PrusaSlicer vs Cura (Cura wins, but just barely, since both are professionally supported with full-time developers): https://all3dp.com/2/prusaslicer-vs-cura-differences/

[update END]

Note that I have printed many ToyBox-designed models perfectly with this printer over the last 24 hrs.

I have also split the model (to cut the last few cm off the end and shorten it) using this technique here in TinkerCad, then exported the part as a shorter part so I could print on the smaller bed of the ToyBox printer.

Here is what the "key" is supposed to look like:

3D rendering of 'key'

And here is how it comes out instead. Notice the misaligned teeth and layers about halfway through. Once I saw it was botched, I stopped the print early.

Side view of 3D printed 'key'

Top view of 3D printed 'key'

Angled view of 3D printed 'key'

Back view of 3D printed 'key'

How can I make it print properly and/or how can I fix the .stl file?


  • My operating system is Linux Ubuntu 20.04
  • I have Windows 10 running in the VirtualBox virtual machine in case I need to run Fusion 360 or something in Windows
  • I tried installing Meshmixer inside Windows 10 and it won't open. I had read online it can be used to fix .stl files, so I was going to look into that. Screenshot of Meshmixer Error Report dialog box


  • $\begingroup$ That looks like a problem with your printer, not the model. $\endgroup$
    – Trish
    Nov 28, 2021 at 23:24
  • 2
    $\begingroup$ This looks like layer shifting, thus a printer problem, not the model. $\endgroup$
    – 0scar
    Nov 30, 2021 at 1:05

3 Answers 3


I have printed at least 5 of them (Cura Slicer, Creality CR10s) and there have been no problems. So I can't understand your problems. I would suggest to use another slicer (Cura). I have now repaired the file with Meshmixer and added it (copter_key-175_meshmixer-repair.stl). Maybe this solves your problem. https://www.thingiverse.com/thing:4551901

  • $\begingroup$ Welcome to 3D Printing SE and thank you for your contribution. When you get a chance, please take the tour to understand how the site works and how it is different than others. $\endgroup$
    – agarza
    Nov 28, 2021 at 14:09
  • $\begingroup$ Can you please post exact detailed instructions on how you did the meshmix repair? That seems to have solved my issue entirely (I'm doing some more testing now to be sure). If you didn't want to explain in detail how you did the meshmixer repair, doing it again while screen-recording (see my instructions here) with OBS Studio, and then posting that to YouTube, would also work. $\endgroup$ Nov 29, 2021 at 0:59

ToyBox 3D printer true print dimensions and limit switch problems

So I figured out that the problem is my print area is so small the printer was occasionally fully pressing and triggering the end-point limit switches! This apparently causes it to stop slightly early, shifting the next layer as it prints.

The printer specs state that it has a print volume of 9 x 8 x 10 cm. However, the print design area and viewer at https://www.make.toys/ shows the design volume like this

Screenshot of ToyBox viewer

In the square grid shown on the base plate there is 1 cm per square, except that as you can see, the far left and far-right columns are < 1 square. Therefore, looking at this image, the usable bed area appears to be about 7.25 cm x 8 cm (the grid size shown in the images), NOT 8 cm x 9 cm.

Furthermore, if you do NOT have the "Skip First Ring" option checked on the "Build" tab in the image below, the printer does a "wipe clean" maneuver in the shape of a spiral, circle, or ring around the object to be printed just before beginning the print. This wipes off any dangling stray print material before beginning the print. If your object fully covers the print bed dimensions, however, that ring will be even wider, causing the printer to hit its limit switches.

(The model in this image is 10.4 cm long, which is too long, causing my printer to hit its limit switches, skewing the layers while printing.)

Screenshot of ToyBox viewer with the 'Skip First Ring' option highlighted

So, the problem is that my part is too big. WithOUT that "Skip First Ring" box checked, the dimensions are probably further reduced by another 5 mm or so on X and Y dimensions, bringing it down to about 6.75 cm x 7.5 cm usable print area. My part was 10.4 cm long. The Pythagorean Theorem says that $A^2 + B^2 = C^2$, so $C = \sqrt(A^2 + B^2)$ = $\sqrt(6.75cm^2 + 7.5cm^2)$ = 10.09 cm max on the diagonal. My 10.4 cm long part was too long. The printer hit the limit switches, botching the layers.

Had I checked that box maybe I could have gotten away with a part closer to $\sqrt(7.25^2 + 8^2)$ = 10.8 cm long, but that's really pushing the limits of this printer. In the end, shrinking the part a bit more to be about 10 cm or less was all I needed to do!

UPDATE: I've also proven conclusively by designing in www.TinkerCad.com and printing on the ToyBox that the max allowed print height is exactly 9 cm, and it will indeed print properly all the way up to that height.

I'd still like a flying propeller

That being said, even though the "key" of the model in my question printed pretty well in the end, the helicopter blade (propeller) printed horribly because the design is flawed and has a bunch of missing material and air gaps around the hub, making the propeller completely unusable!

Instead, I switched to this thing shown below, shrunk it down to 0.6x to fit my printer, set my printer settings from medium to fine resolution, and got pretty good results! I still need to further tweak and edit the design on https://www.tinkercad.com to give the pull key better clearance, and better connection with the hub gear, and I think I'll be able to get a great result! I got it to fly a few times up to 8 ft high or so, but the pull is very rough and inconsistent, so the model needs further tweaking.

Screenshot of the Thingiverse page for the helicopter model

Keywords: ToyBox 3D printer helicopter and toybox printer clearances, print dimensions, print volume, specs, print settings

  • $\begingroup$ @agarza, thanks for the helpful edits. Just one question: why did you use the HTML &nbsp; code to add spaces to my answer instead of just pressing Space Bar to add a space (` `)? $\endgroup$ Dec 10, 2021 at 17:29
  • 2
    $\begingroup$ &nbsp; is a Non-Breaking SPace that prevents line breaks between characters, specifically like units of measurement. More information is available here, here, and here. $\endgroup$
    – agarza
    Dec 10, 2021 at 20:37
  • 1
    $\begingroup$ We follow the rule for units having a non-breaking space here. another alternative is to use the unicode to get the non-breaking space (Alt+0160). $\endgroup$
    – Trish
    Dec 21, 2021 at 8:41

Non-manifold objects are only accidentally solid, as sometimes it becomes unclear what is the inside and what is the outside. Some slicers attempt to fix this and do a good job of guessing how to correct it. Also, some non-manifold errors are easier to fix than others.

If your slicer is complaining about a part file being non-manifold or you suspect that this is causing a problem, you should bring it into a surface mesh editor like meshlab or blender and try to fix it with the manifold test and repair tools in either of these programs.

Typical ways an STL file could be non-manifold include:

  • cracks between faces caused by round off error
  • missing faces
  • flipped faces
  • interior faces
  • faces that intersect somewhere other than an edge

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